presentation on types of memory

Types of Memory

Reviewed by Psychology Today Staff

A person’s memory is a sea of images and other sensory impressions, facts and meanings, echoes of past feelings, and ingrained codes for how to behave—a diverse well of information. Naturally, there are many ways (some experts suggest there are hundreds) to describe the varieties of what people remember and how. While the different brands of memory are not always described in exactly the same way by memory researchers, some key concepts have emerged.

These forms of memory, which can overlap in daily life, have also been arranged into broad categories. Memory that lingers for a moment (or even less than a second) could be described as short-term memory , while any kind of information that is preserved for remembering at a later point can be called long-term memory . Memory experts have also distinguished explicit memory , in which information is consciously recalled, from implicit memory , the use of saved information without conscious awareness that it’s being recalled.

On This Page

• Episodic Memory
• Semantic Memory
• Procedural Memory
• Short-Term Memory and Working Memory
• Sensory Memory
• Prospective Memory

When a person recalls a particular event (or “episode”) experienced in the past, that is episodic memory . This kind of long-term memory brings to attention details about anything from what one ate for breakfast to the emotions that were stirred up during a serious conversation with a romantic partner. The experiences conjured by episodic memory can be very recent or decades-old.

A related concept is autobiographical memory , which is the memory of information that forms part of a person’s life story. However, while autobiographical memory includes memories of events in one’s life (such as one’s sixteenth birthday party), it can also encompass facts (such as one’s birth date) and other non-episodic forms of information.

• The details of a phone call you had 20 minutes ago

• How you felt during your last argument

• What it was like receiving your high-school diploma

Semantic memory is someone’s long-term store of knowledge: It’s composed of pieces of information such as facts learned in school, what concepts mean and how they are related, or the definition of a particular word. The details that make up semantic memory can correspond to other forms of memory. One may remember factual details about a party, for instance—what time it started, at whose house it took place, how many people were there, all part of semantic memory—in addition to recalling the sounds heard and excitement felt. But semantic memory can also include facts and meanings related to people, places, or things one has no direct relation to.

• What year it currently is

• The capital of a foreign country

• The meaning of a slang term

Sitting on a bike after not riding one for years and recalling just what to do is a quintessential example of procedural memory . The term describes long-term memory for how to do things, both physical and mental, and is involved in the process of learning skills—from the basic ones people take for granted to those that require considerable practice. A related term is kinesthetic memory , which refers specifically to memory for physical behaviors.

• How to tie your shoes

• How to send an email

• How to shoot a basketball

The terms short-term memory and working memory are sometimes used interchangeably, and both refer to storage of information for a brief amount of time. Working memory can be distinguished from general short-term memory, however, in that working memory specifically involves the temporary storage of information that is being mentally manipulated.

Short-term memory is used when, for instance, the name of a new acquaintance, a statistic, or some other detail is consciously processed and retained for at least a short period of time. It may then be saved in long-term memory, or it may be forgotten within minutes. With working memory , information—the preceding words in a sentence one is reading, for example—is held in mind so that it can be used in the moment.

• The appearance of someone you met a minute ago

• The current temperature, immediately after looking it up

• What happened moments ago in a movie

• A number you have calculated as part of a mental math problem

• The person named at the beginning of a sentence

• Holding a concept in mind (such as ball ) and combining it with another ( orange )

Sensory memories are what psychologists call the short-term memories of just-experienced sensory stimuli such as sights and sounds. The brief memory of something just seen has been called iconic memory, while the sound-based equivalent is called echoic memory. Additional forms of short-term sensory memory are thought to exist for the other senses as well.

Sense-related memories, of course, can also be preserved long-term. Visual-spatial memory refers to memory of how objects are organized in space—tapped when a person remembers which way to walk to get to the grocery store. Auditory memory , olfactory memory , and haptic memory are terms for stored sensory impressions of sounds, smells, and skin sensations, respectively.

• The sound of a piano note that was just played

• The appearance of a car that drove by

• The smell of a restaurant you passed

Prospective memory is forward-thinking memory: It means recalling an intention from the past in order to do something in the future. It is essential for daily functioning, in that memories of previous intentions, including very recent ones, ensure that people execute their plans and meet their obligations when the intended behaviors can’t be carried out right away, or have to be carried out routinely.

• To call someone back

• To stop at the drugstore on the way home

• To pay the rent every month

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Different Types of Memories

The 4 Main Types of Memory and the Function of Each

Toketemu has been multimedia storyteller for the last four years. Her expertise focuses primarily on mental wellness and women’s health topics. 

Huma Sheikh, MD, is a board-certified neurologist, specializing in migraine and stroke, and affiliated with Mount Sinai of New York.

Jan Hakan Dahlstrom / Getty Images

• 4 Main Types
• Their Function
• How They're Formed
• Ways to Improve

Memory is the ability to store and retrieve information when people need it. The four general types of memories are sensory memory, short-term memory, working memory, and long-term memory. Long-term memory can be further categorized as either implicit (unconscious) or explicit (conscious).

Together, these types of memory make us who we are as individuals, yet we don’t put a lot of thought into how memory works. It’s a phenomenon that involves several processes and can be split into different types, each of which plays an important role in the retention and recall of information.

4 Main Types of Memories 

For years, researchers and experts have debated the classification of memories. Many experts agree that there are four main categories of memory. All other types of memory tend to fall under these four major categories. 

Memory is sometimes also classified into stages and processes. People who classify memory into only two distinctive types, implicit and explicit memory , view that other types of memories like sensory, short-term, and long-term memories aren’t types of memory but stages of memory .

Sensory Memory 

Sensory memory allows you to remember sensory information after the stimulation has ended. Researchers who classify memory more as stages than types believe that all other memories begin with the formation of sensory memories. Typically your sensory memory only holds onto information for brief periods. Remembering the sensation of a person’s touch or a sound you heard in passing is sensory memory.

When a sensory experience keeps recurring, and you start to attach other memories to it, the sensory experience stops living in your sensory memory. It might move to your short-term memory or more permanently to your long-term memory.

There are three types of sensory memory: iconic , which is obtained through sight; echoic, which is auditory; and haptic, which is through touch.

Short-term Memory 

As the name implies, short-term memory allows you to recall specific information about anything for a brief period. Short-term memory is not as fleeting as sensory memory, but it’s also not as permanent as long-term memory. Short-term memory is also known as primary or active memory.

Research estimates that short-term memories only last for about 30 seconds. When you read a line in a book or a string of numbers that you have to recall, that’s your short-term memory at work.

You can keep information in your short-term memory by rehearsing the information. For example, if you need to recall a string of numbers, you might keep repeating them to yourself until you input them. However, if you are asked to recall those numbers about 10 minutes after inputting them, you’d most likely be unable to. 

Working Memory

Working memory is a type of memory that involves the immediate and small amount of information that a person actively uses as they perform cognitive tasks.

While some experts view working memory as a fourth distinct type of memory, working memory can fall under the classification of short-term memory and, in many cases, is even used interchangeably. 

Long-term Memory

We store a vast majority of our memories in our long-term memory . Any memory we can still recall after 30 seconds could classify as long-term memory. These memories range in significance—from recalling the name of a friendly face at your favorite coffee shop to important bits of information like a close friend’s birthday or your home address.

There is no limit to how much our long-term memory can hold and for how long. We can further split long-term memory into two main categories: explicit and implicit long-term memory.

Explicit Long-term Memory  

Explicit long-term memories are memories we consciously and deliberately took time to form and recall. Explicit memory holds information such as your best friend’s birthday or your phone number. It often includes major milestones in your life, such as childhood events, graduation dates, or academic work you learned in school.

In general, explicit memories can be episodic or semantic.

• Episodic memories are formed from particular episodes in your life. Examples of episodic memory include the first time you rode a bike or your first day at school.
• Semantic memories are general facts and bits of information you absorbed over the years. For instance, when you recall a random fact while filling in a crossword puzzle, you pull it from your semantic memory.

Conditions such as Alzheimer’s disease heavily affect explicit memories.

Implicit Long-term Memory 

We are not as deliberate with forming implicit memories as we are with explicit ones. Implicit memories form unconsciously and might affect the way a person thinks and behaves.

Implicit memory often comes into play when we are learning motor skills like walking or riding a bike. If you learned how to ride a bike when you were 10 and only ever pick it up again when you are 20, implicit memory helps you remember how to ride it. 

We can retrieve long-term memories a few different ways. The three types of memory retrieval are recall, recognition, and relearning.

Why Do We Have Different Types of Memory?

Each different type of memory we have is important, and they all have various functions. Your short-term memory allows you to process and understand the information in an instant. When you read a paragraph in a book and understand it, that’s your short-term memory at work. 

Your most treasured and important memories are held in your long-term memory. Your long-term memory facilitates how to walk, talk, ride a bike, and engage in daily activities. It also allows you to recall important dates and facts.

In your day-to-day activities, you are bound to find yourself relying on your long-term memory the most. From waking up and brushing your teeth to getting on the right bus to commute to work, recalling all of these steps is facilitated by your long-term memory. 

How These Types of Memories Are Formed

Memories are made in three distinct stages. It starts with encoding. Encoding is the way external stimuli and information make their way into your brain. This could occur through any of your five senses.

The next stage is storage, where the information we take in is stored either briefly, like with sensory and short term memory, or more permanently, like with long term memory.

The final stage is recall. Recall is our ability to retrieve the memory we’ve made from where it is stored. These processes are also how sensory memory might be turned into short-term memory or short-term memory into long-term memory. 

How to Improve Your Memory 

It’s commonplace to hear people complain about having poor memory . When we try to recall information we have encoded and stored, and we can’t, then our memory has failed us.

The good news is that it is possible to improve your memory and make the process of encoding, storing, and recalling information more seamless. Here are a couple of tips that could help you improve your memory : 

• Take care of your body . If you take care of your body by eating a balanced diet, exercising regularly, and getting enough sleep, you improve your brain health which helps you process and recall memories better. 
• Exercise your mind . There are several activities and puzzles you could do to give your mind a great workout. 
• Take advantage of calendars and planners . Clear up memory space in your brain by using calendars and planners to remember the little things like shopping lists and meeting times. 
• Stay mentally active . Reading, writing, and constantly learning help you remain mentally active, which can improve your memory.

Stangor C, Walinga J. 9. 1 Memories as types and stages . In: Introduction to Psychology 1st Canadian Edition . BCcampus; 2014.

Camina E, Güell F. The neuroanatomical, neurophysiological and psychological basis of memory: current models and their origins .  Front Pharmacol . 2017;8:438. doi:10.3389/fphar.2017.00438

Cascella M, Al Khalili Y. Short term memory impairment. In: StatPearls. StatPearls Publishing; 2021.

Queensland Brain Institute. Types of memory.

University of Central Florida. General psychology: Retrieval .

Harvard Health. 7 ways to keep your memory sharp at any age .

By Toketemu Ohwovoriole Toketemu has been multimedia storyteller for the last four years. Her expertise focuses primarily on mental wellness and women’s health topics.

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

8.1 Memories as Types and Stages

Learning objectives.

• Compare and contrast explicit and implicit memory, identifying the features that define each.
• Explain the function and duration of eidetic and echoic memories.
• Summarize the capacities of short-term memory and explain how working memory is used to process information in it.

As you can see in Table 8.1 “Memory Conceptualized in Terms of Types, Stages, and Processes” , psychologists conceptualize memory in terms of types , in terms of stages , and in terms of processes . In this section we will consider the two types of memory, explicit memory and implicit memory , and then the three major memory stages: sensory , short-term , and long-term (Atkinson & Shiffrin, 1968). Then, in the next section, we will consider the nature of long-term memory, with a particular emphasis on the cognitive techniques we can use to improve our memories. Our discussion will focus on the three processes that are central to long-term memory: encoding , storage , and retrieval .

Table 8.1 Memory Conceptualized in Terms of Types, Stages, and Processes

Explicit Memory

When we assess memory by asking a person to consciously remember things, we are measuring explicit memory . Explicit memory refers to knowledge or experiences that can be consciously remembered . As you can see in Figure 8.2 “Types of Memory” , there are two types of explicit memory: episodic and semantic . Episodic memory refers to the firsthand experiences that we have had (e.g., recollections of our high school graduation day or of the fantastic dinner we had in New York last year). Semantic memory refers to our knowledge of facts and concepts about the world (e.g., that the absolute value of −90 is greater than the absolute value of 9 and that one definition of the word “affect” is “the experience of feeling or emotion”).

Figure 8.2 Types of Memory

Explicit memory is assessed using measures in which the individual being tested must consciously attempt to remember the information. A recall memory test is a measure of explicit memory that involves bringing from memory information that has previously been remembered . We rely on our recall memory when we take an essay test, because the test requires us to generate previously remembered information. A multiple-choice test is an example of a recognition memory test , a measure of explicit memory that involves determining whether information has been seen or learned before .

Your own experiences taking tests will probably lead you to agree with the scientific research finding that recall is more difficult than recognition. Recall, such as required on essay tests, involves two steps: first generating an answer and then determining whether it seems to be the correct one. Recognition, as on multiple-choice test, only involves determining which item from a list seems most correct (Haist, Shimamura, & Squire, 1992). Although they involve different processes, recall and recognition memory measures tend to be correlated. Students who do better on a multiple-choice exam will also, by and large, do better on an essay exam (Bridgeman & Morgan, 1996).

A third way of measuring memory is known as relearning (Nelson, 1985). Measures of relearning (or savings) assess how much more quickly information is processed or learned when it is studied again after it has already been learned but then forgotten . If you have taken some French courses in the past, for instance, you might have forgotten most of the vocabulary you learned. But if you were to work on your French again, you’d learn the vocabulary much faster the second time around. Relearning can be a more sensitive measure of memory than either recall or recognition because it allows assessing memory in terms of “how much” or “how fast” rather than simply “correct” versus “incorrect” responses. Relearning also allows us to measure memory for procedures like driving a car or playing a piano piece, as well as memory for facts and figures.

Implicit Memory

While explicit memory consists of the things that we can consciously report that we know, implicit memory refers to knowledge that we cannot consciously access. However, implicit memory is nevertheless exceedingly important to us because it has a direct effect on our behavior. Implicit memory refers to the influence of experience on behavior, even if the individual is not aware of those influences . As you can see in Figure 8.2 “Types of Memory” , there are three general types of implicit memory: procedural memory, classical conditioning effects, and priming.

Procedural memory refers to our often unexplainable knowledge of how to do things . When we walk from one place to another, speak to another person in English, dial a cell phone, or play a video game, we are using procedural memory. Procedural memory allows us to perform complex tasks, even though we may not be able to explain to others how we do them. There is no way to tell someone how to ride a bicycle; a person has to learn by doing it. The idea of implicit memory helps explain how infants are able to learn. The ability to crawl, walk, and talk are procedures, and these skills are easily and efficiently developed while we are children despite the fact that as adults we have no conscious memory of having learned them.

A second type of implicit memory is classical conditioning effects, in which we learn, often without effort or awareness, to associate neutral stimuli (such as a sound or a light) with another stimulus (such as food), which creates a naturally occurring response, such as enjoyment or salivation. The memory for the association is demonstrated when the conditioned stimulus (the sound) begins to create the same response as the unconditioned stimulus (the food) did before the learning.

The final type of implicit memory is known as priming , or changes in behavior as a result of experiences that have happened frequently or recently . Priming refers both to the activation of knowledge (e.g., we can prime the concept of “kindness” by presenting people with words related to kindness) and to the influence of that activation on behavior (people who are primed with the concept of kindness may act more kindly).

One measure of the influence of priming on implicit memory is the word fragment test , in which a person is asked to fill in missing letters to make words. You can try this yourself: First, try to complete the following word fragments, but work on each one for only three or four seconds. Do any words pop into mind quickly?

_ i b _ a _ y

_ h _ s _ _ i _ n

_ h _ i s _

Now read the following sentence carefully:

Then try again to make words out of the word fragments.

I think you might find that it is easier to complete fragments 1 and 3 as “library” and “book,” respectively, after you read the sentence than it was before you read it. However, reading the sentence didn’t really help you to complete fragments 2 and 4 as “physician” and “chaise.” This difference in implicit memory probably occurred because as you read the sentence, the concept of “library” (and perhaps “book”) was primed, even though they were never mentioned explicitly. Once a concept is primed it influences our behaviors, for instance, on word fragment tests.

Our everyday behaviors are influenced by priming in a wide variety of situations. Seeing an advertisement for cigarettes may make us start smoking, seeing the flag of our home country may arouse our patriotism, and seeing a student from a rival school may arouse our competitive spirit. And these influences on our behaviors may occur without our being aware of them.

Research Focus: Priming Outside Awareness Influences Behavior

One of the most important characteristics of implicit memories is that they are frequently formed and used automatically , without much effort or awareness on our part. In one demonstration of the automaticity and influence of priming effects, John Bargh and his colleagues (Bargh, Chen, & Burrows, 1996) conducted a study in which they showed college students lists of five scrambled words, each of which they were to make into a sentence. Furthermore, for half of the research participants, the words were related to stereotypes of the elderly. These participants saw words such as the following:

The other half of the research participants also made sentences, but from words that had nothing to do with elderly stereotypes. The purpose of this task was to prime stereotypes of elderly people in memory for some of the participants but not for others.

The experimenters then assessed whether the priming of elderly stereotypes would have any effect on the students’ behavior—and indeed it did. When the research participant had gathered all of his or her belongings, thinking that the experiment was over, the experimenter thanked him or her for participating and gave directions to the closest elevator. Then, without the participants knowing it, the experimenters recorded the amount of time that the participant spent walking from the doorway of the experimental room toward the elevator. As you can see in Figure 8.3 “Results From Bargh, Chen, and Burrows, 1996” , participants who had made sentences using words related to elderly stereotypes took on the behaviors of the elderly—they walked significantly more slowly as they left the experimental room.

Figure 8.3 Results From Bargh, Chen, and Burrows, 1996

Bargh, Chen, and Burrows (1996) found that priming words associated with the elderly made people walk more slowly.

Adapted from Bargh, J. A., Chen, M., & Burrows, L. (1996). Automaticity of social behavior: Direct effects of trait construct and stereotype activation on action. Journal of Personality & Social Psychology, 71 , 230–244.

To determine if these priming effects occurred out of the awareness of the participants, Bargh and his colleagues asked still another group of students to complete the priming task and then to indicate whether they thought the words they had used to make the sentences had any relationship to each other, or could possibly have influenced their behavior in any way. These students had no awareness of the possibility that the words might have been related to the elderly or could have influenced their behavior.

Stages of Memory: Sensory, Short-Term, and Long-Term Memory

Another way of understanding memory is to think about it in terms of stages that describe the length of time that information remains available to us. According to this approach (see Figure 8.4 “Memory Duration” ), information begins in sensory memory , moves to short-term memory , and eventually moves to long-term memory . But not all information makes it through all three stages; most of it is forgotten. Whether the information moves from shorter-duration memory into longer-duration memory or whether it is lost from memory entirely depends on how the information is attended to and processed.

Figure 8.4 Memory Duration

Memory can characterized in terms of stages—the length of time that information remains available to us.

Adapted from Atkinson, R. C., & Shiffrin, R. M. (1968). Human memory: A proposed system and its control processes. In K. Spence (Ed.), The psychology of learning and motivation (Vol. 2). Oxford, England: Academic Press.

Sensory Memory

Sensory memory refers to the brief storage of sensory information . Sensory memory is a memory buffer that lasts only very briefly and then, unless it is attended to and passed on for more processing, is forgotten. The purpose of sensory memory is to give the brain some time to process the incoming sensations, and to allow us to see the world as an unbroken stream of events rather than as individual pieces.

Visual sensory memory is known as iconic memory . Iconic memory was first studied by the psychologist George Sperling (1960). In his research, Sperling showed participants a display of letters in rows, similar to that shown in Figure 8.5 “Measuring Iconic Memory” . However, the display lasted only about 50 milliseconds (1/20 of a second). Then, Sperling gave his participants a recall test in which they were asked to name all the letters that they could remember. On average, the participants could remember only about one-quarter of the letters that they had seen.

Figure 8.5 Measuring Iconic Memory

Sperling (1960) showed his participants displays such as this one for only 1/20th of a second. He found that when he cued the participants to report one of the three rows of letters, they could do it, even if the cue was given shortly after the display had been removed. The research demonstrated the existence of iconic memory.

Adapted from Sperling, G. (1960). The information available in brief visual presentation. Psychological Monographs, 74 (11), 1–29.

Sperling reasoned that the participants had seen all the letters but could remember them only very briefly, making it impossible for them to report them all. To test this idea, in his next experiment he first showed the same letters, but then after the display had been removed , he signaled to the participants to report the letters from either the first, second, or third row. In this condition, the participants now reported almost all the letters in that row. This finding confirmed Sperling’s hunch: Participants had access to all of the letters in their iconic memories, and if the task was short enough, they were able to report on the part of the display he asked them to. The “short enough” is the length of iconic memory, which turns out to be about 250 milliseconds (¼ of a second).

Auditory sensory memory is known as echoic memory . In contrast to iconic memories, which decay very rapidly, echoic memories can last as long as 4 seconds (Cowan, Lichty, & Grove, 1990). This is convenient as it allows you—among other things—to remember the words that you said at the beginning of a long sentence when you get to the end of it, and to take notes on your psychology professor’s most recent statement even after he or she has finished saying it.

In some people iconic memory seems to last longer, a phenomenon known as eidetic imagery (or “photographic memory”) in which people can report details of an image over long periods of time. These people, who often suffer from psychological disorders such as autism, claim that they can “see” an image long after it has been presented, and can often report accurately on that image. There is also some evidence for eidetic memories in hearing; some people report that their echoic memories persist for unusually long periods of time. The composer Wolfgang Amadeus Mozart may have possessed eidetic memory for music, because even when he was very young and had not yet had a great deal of musical training, he could listen to long compositions and then play them back almost perfectly (Solomon, 1995).

Short-Term Memory

Most of the information that gets into sensory memory is forgotten, but information that we turn our attention to, with the goal of remembering it, may pass into short-term memory . Short-term memory (STM) is the place where small amounts of information can be temporarily kept for more than a few seconds but usually for less than one minute (Baddeley, Vallar, & Shallice, 1990). Information in short-term memory is not stored permanently but rather becomes available for us to process, and the processes that we use to make sense of, modify, interpret, and store information in STM are known as working memory .

Although it is called “memory,” working memory is not a store of memory like STM but rather a set of memory procedures or operations. Imagine, for instance, that you are asked to participate in a task such as this one, which is a measure of working memory (Unsworth & Engle, 2007). Each of the following questions appears individually on a computer screen and then disappears after you answer the question:

Is 10 × 2 − 5 = 15? (Answer YES OR NO) Then remember “S”

Is 12 ÷ 6 − 2 = 1? (Answer YES OR NO) Then remember “R”

Is 10 × 2 = 5? (Answer YES OR NO) Then remember “P”

Is 8 ÷ 2 − 1 = 1? (Answer YES OR NO) Then remember “T”

Is 6 × 2 − 1 = 8? (Answer YES OR NO) Then remember “U”

Is 2 × 3 − 3 = 0? (Answer YES OR NO) Then remember “Q”

To successfully accomplish the task, you have to answer each of the math problems correctly and at the same time remember the letter that follows the task. Then, after the six questions, you must list the letters that appeared in each of the trials in the correct order (in this case S, R, P, T, U, Q).

To accomplish this difficult task you need to use a variety of skills. You clearly need to use STM, as you must keep the letters in storage until you are asked to list them. But you also need a way to make the best use of your available attention and processing. For instance, you might decide to use a strategy of “repeat the letters twice, then quickly solve the next problem, and then repeat the letters twice again including the new one.” Keeping this strategy (or others like it) going is the role of working memory’s central executive —the part of working memory that directs attention and processing. The central executive will make use of whatever strategies seem to be best for the given task. For instance, the central executive will direct the rehearsal process, and at the same time direct the visual cortex to form an image of the list of letters in memory. You can see that although STM is involved, the processes that we use to operate on the material in memory are also critical.

Short-term memory is limited in both the length and the amount of information it can hold. Peterson and Peterson (1959) found that when people were asked to remember a list of three-letter strings and then were immediately asked to perform a distracting task (counting backward by threes), the material was quickly forgotten (see Figure 8.6 “STM Decay” ), such that by 18 seconds it was virtually gone.

Figure 8.6 STM Decay

Peterson and Peterson (1959) found that information that was not rehearsed decayed quickly from memory.

Adapted from Peterson, L., & Peterson, M. J. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology, 58 (3), 193–198.

One way to prevent the decay of information from short-term memory is to use working memory to rehearse it. Maintenance rehearsal is the process of repeating information mentally or out loud with the goal of keeping it in memory . We engage in maintenance rehearsal to keep a something that we want to remember (e.g., a person’s name, e-mail address, or phone number) in mind long enough to write it down, use it, or potentially transfer it to long-term memory.

If we continue to rehearse information it will stay in STM until we stop rehearsing it, but there is also a capacity limit to STM. Try reading each of the following rows of numbers, one row at a time, at a rate of about one number each second. Then when you have finished each row, close your eyes and write down as many of the numbers as you can remember.

If you are like the average person, you will have found that on this test of working memory, known as a digit span test , you did pretty well up to about the fourth line, and then you started having trouble. I bet you missed some of the numbers in the last three rows, and did pretty poorly on the last one.

The digit span of most adults is between five and nine digits, with an average of about seven. The cognitive psychologist George Miller (1956) referred to “seven plus or minus two” pieces of information as the “magic number” in short-term memory. But if we can only hold a maximum of about nine digits in short-term memory, then how can we remember larger amounts of information than this? For instance, how can we ever remember a 10-digit phone number long enough to dial it?

One way we are able to expand our ability to remember things in STM is by using a memory technique called chunking . Chunking is the process of organizing information into smaller groupings (chunks), thereby increasing the number of items that can be held in STM . For instance, try to remember this string of 12 letters:

You probably won’t do that well because the number of letters is more than the magic number of seven.

Now try again with this one:

Would it help you if I pointed out that the material in this string could be chunked into four sets of three letters each? I think it would, because then rather than remembering 12 letters, you would only have to remember the names of four television stations. In this case, chunking changes the number of items you have to remember from 12 to only four.

Experts rely on chunking to help them process complex information. Herbert Simon and William Chase (1973) showed chess masters and chess novices various positions of pieces on a chessboard for a few seconds each. The experts did a lot better than the novices in remembering the positions because they were able to see the “big picture.” They didn’t have to remember the position of each of the pieces individually, but chunked the pieces into several larger layouts. But when the researchers showed both groups random chess positions—positions that would be very unlikely to occur in real games—both groups did equally poorly, because in this situation the experts lost their ability to organize the layouts (see Figure 8.7 “Possible and Impossible Chess Positions” ). The same occurs for basketball. Basketball players recall actual basketball positions much better than do nonplayers, but only when the positions make sense in terms of what is happening on the court, or what is likely to happen in the near future, and thus can be chunked into bigger units (Didierjean & Marmèche, 2005).

Figure 8.7 Possible and Impossible Chess Positions

Experience matters: Experienced chess players are able to recall the positions of the game on the right much better than are those who are chess novices. But the experts do no better than the novices in remembering the positions on the left, which cannot occur in a real game.

If information makes it past short term-memory it may enter long-term memory (LTM) , memory storage that can hold information for days, months, and years . The capacity of long-term memory is large, and there is no known limit to what we can remember (Wang, Liu, & Wang, 2003). Although we may forget at least some information after we learn it, other things will stay with us forever. In the next section we will discuss the principles of long-term memory.

Key Takeaways

• Memory refers to the ability to store and retrieve information over time.
• For some things our memory is very good, but our active cognitive processing of information assures that memory is never an exact replica of what we have experienced.
• Explicit memory refers to experiences that can be intentionally and consciously remembered, and it is measured using recall, recognition, and relearning. Explicit memory includes episodic and semantic memories.
• Measures of relearning (also known as savings) assess how much more quickly information is learned when it is studied again after it has already been learned but then forgotten.
• Implicit memory refers to the influence of experience on behavior, even if the individual is not aware of those influences. The three types of implicit memory are procedural memory, classical conditioning, and priming.
• Information processing begins in sensory memory, moves to short-term memory, and eventually moves to long-term memory.
• Maintenance rehearsal and chunking are used to keep information in short-term memory.
• The capacity of long-term memory is large, and there is no known limit to what we can remember.

Exercises and Critical Thinking

• List some situations in which sensory memory is useful for you. What do you think your experience of the stimuli would be like if you had no sensory memory?
• Describe a situation in which you need to use working memory to perform a task or solve a problem. How do your working memory skills help you?

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Nelson, T. O. (1985). Ebbinghaus’s contribution to the measurement of retention: Savings during relearning. Journal of Experimental Psychology: Learning, Memory, and Cognition, 11 (3), 472–478.

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Simon, H. A., & Chase, W. G. (1973). Skill in chess. American Scientist, 61 (4), 394–403.

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Unsworth, N., & Engle, R. W. (2007). On the division of short-term and working memory: An examination of simple and complex span and their relation to higher order abilities. Psychological Bulletin, 133 (6), 1038–1066.

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Cognitive neuroscience perspective on memory: overview and summary

Sruthi sridhar.

1 Department of Psychology, Mount Allison University, Sackville, NB, Canada

Abdulrahman Khamaj

2 Department of Industrial Engineering, College of Engineering, Jazan University, Jazan, Saudi Arabia

Manish Kumar Asthana

3 Department of Humanities and Social Sciences, Indian Institute of Technology Roorkee, Roorkee, India

4 Department of Design, Indian Institute of Technology Roorkee, Roorkee, India

Associated Data

The original contributions presented in this study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

This paper explores memory from a cognitive neuroscience perspective and examines associated neural mechanisms. It examines the different types of memory: working, declarative, and non-declarative, and the brain regions involved in each type. The paper highlights the role of different brain regions, such as the prefrontal cortex in working memory and the hippocampus in declarative memory. The paper also examines the mechanisms that underlie the formation and consolidation of memory, including the importance of sleep in the consolidation of memory and the role of the hippocampus in linking new memories to existing cognitive schemata. The paper highlights two types of memory consolidation processes: cellular consolidation and system consolidation. Cellular consolidation is the process of stabilizing information by strengthening synaptic connections. System consolidation models suggest that memories are initially stored in the hippocampus and are gradually consolidated into the neocortex over time. The consolidation process involves a hippocampal-neocortical binding process incorporating newly acquired information into existing cognitive schemata. The paper highlights the role of the medial temporal lobe and its involvement in autobiographical memory. Further, the paper discusses the relationship between episodic and semantic memory and the role of the hippocampus. Finally, the paper underscores the need for further research into the neurobiological mechanisms underlying non-declarative memory, particularly conditioning. Overall, the paper provides a comprehensive overview from a cognitive neuroscience perspective of the different processes involved in memory consolidation of different types of memory.

Introduction

Memory is an essential cognitive function that permits individuals to acquire, retain, and recover data that defines a person’s identity ( Zlotnik and Vansintjan, 2019 ). Memory is a multifaceted cognitive process that involves different stages: encoding, consolidation, recovery, and reconsolidation. Encoding involves acquiring and processing information that is transformed into a neuronal representation suitable for storage ( Liu et al., 2021 ; Panzeri et al., 2023 ). The information can be acquired through various channels, such as visual, auditory, olfactory, or tactile inputs. The acquired sensory stimuli are converted into a format the brain can process and retain. Different factors such as attention, emotional significance, and repetition can influence the encoding process and determine the strength and durability of the resulting memory ( Squire et al., 2004 ; Lee et al., 2016 ; Serences, 2016 ).

Consolidation includes the stabilization and integration of memory into long-term storage to increase resistance to interference and decay ( Goedert and Willingham, 2002 ). This process creates enduring structural modification in the brain and thereby has consequential effects on the function by reorganizing and strengthening neural connections. Diverse sources like sleep and stress and the release of neurotransmitters can influence memory consolidation. Many researchers have noted the importance of sleep due to its critical role in enabling a smooth transition of information from transient repositories into more stable engrams (memory traces) ( McGaugh, 2000 ; Clawson et al., 2021 ; Rakowska et al., 2022 ).

Retrieval involves accessing, selecting, and reactivating or reconstructing the stored memory to allow conscious access to previously encoded information ( Dudai, 2002 ). Retrieving memories depends on activating relevant neural pathways while reconstructing encoded information. Factors like contextual or retrieval cues and familiarity with the material can affect this process. Forgetting becomes a possibility if there are inadequate triggers for associated memory traces to activate upon recall. Luckily, mnemonic strategies and retrieval practice offer effective tools to enhance recovery rates and benefit overall memory performance ( Roediger and Butler, 2011 ).

Previous research implied that once a memory has been consolidated, it becomes permanent ( McGaugh, 2000 ; Robins, 2020 ). However, recent studies have found an additional phase called “reconsolidation,” during which stored memories, when reactivated, enter a fragile or liable state and become susceptible to modification or update ( Schiller et al., 2009 ; Asthana et al., 2015 ). The process highlights the notion that memory is not static but a dynamic system influenced by subsequent encounters. The concept of reconsolidation has much significance in memory modification therapies and interventions, as it offers a promising opportunity to target maladaptive or traumatic memories for modification specifically. However, more thorough investigations are needed to gain insight into the mechanisms and concrete implications of employing memory reconsolidation within therapeutic settings ( Bellfy and Kwapis, 2020 ).

The concept of memory is not reducible to a single unitary phenomenon; instead, evidence suggests that it can be subdivided into several distinct but interrelated constituent processes and systems ( Richter-Levin and Akirav, 2003 ). There are three major types of human memory: working memory, declarative memory (explicit), and non-declarative memory (implicit). All these types of memories involve different neural systems in the brain. Working memory is a unique transient active store capable of manipulating information essential for many complex cognitive operations, including language processing, reasoning, and judgment ( Atkinson and Shiffrin, 1968 ; Baddeley and Logie, 1999 ; Funahashi, 2017 ; Quentin et al., 2019 ). Previous models suggest the existence of three components that make up the working memory ( Baddeley and Hitch, 1974 ; Baddeley, 1986 ). One master component, the central executive, controls the two dependent components, the phonological loop (speech perception and language comprehension) and the visuospatial sketchpad (visual images and spatial impressions processing). Some models mention a third component known as the episodic buffer. It is theorized that the episodic buffer serves as an intermediary between perception, long-term memory, and two components of working memory (the phonological loop and visuospatial sketchpad) by storing integrated episodes or chunks from both sources ( Baddeley, 2000 ). Declarative memory (explicit memory) can be recalled consciously, including facts and events that took place in one’s life or information learned from books. It encompasses memories of both autobiographical experiences and memories associated with general knowledge. It is usually associated with the hippocampus–medial temporal lobe system ( Thompson and Kim, 1996 ; Ober, 2014 ). Non-declarative memory (implicit memory) refers to unconscious forms of learning such as skills, habits, and priming effects; this type of implicit learning does not involve conscious recollection but can include motor skill tasks that often require no thought prior to execution nor later recall upon completion. This type of memory usually involves the amygdala and other systems ( Thompson and Kim, 1996 ; Ober, 2014 ).

Working memory

Working memory is primarily associated with the prefrontal and posterior parietal cortex ( Sarnthein et al., 1998 ; Todd and Marois, 2005 ). Working memory is not localized to a single brain region, and research suggests that it is an emergent property arising from functional interactions between the prefrontal cortex (PFC) and the rest of the brain ( D’Esposito, 2007 ). Neuroimaging studies have explored the neural basis for the three components proposed by Baddeley and Hitch (1974) , the Central executive, the phonological loop, and the visuospatial sketch pad; there is evidence for the existence of a fourth component called the episodic buffer ( Baddeley, 2000 ).

The central executive plays a significant role in working memory by acting as the control center ( Shallice, 2002 ). It facilitates critical functions like attention allocation and coordination between the phonological loop and the visuospatial sketchpad ( Yu et al., 2023 ). Recent findings have illuminated the dual-functional network regulation, the cingulo-opercular network (CON) and the frontoparietal network (FPN), that underpins the central executive system ( Yu et al., 2023 ). The CON comprises the dorsal anterior cingulate cortex (dACC) and anterior insula (AI). In contrast, the FPN encompasses various regions, such as the dorsolateral prefrontal cortex (DLPFC) and frontal eye field (FEF), along with the intraparietal sulcus (IPS) ( Yu et al., 2023 ). Neuroimaging research has found evidence that elucidates the neural underpinnings of the executive attention control system to the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) ( Jung et al., 2022 ). The activation patterns indicate that the CON may have a broader top-down control function across the working memory process. At the same time, the FPN could be more heavily implicated in momentary control or processing at the trial level ( Yu et al., 2023 ). Evidence suggests that the central executive interacts with the phonological loop and visuospatial sketchpad to support working memory processes ( Baddeley, 2003 ; Buchsbaum, 2010 ; Menon and D’Esposito, 2021 ). The function, localization, and neural basis of this interaction are thought to involve the activation of specific brain regions associated with each component of working memory, as discussed in detail below.

The phonological loop is divided into two components: a storage system that maintains information (a few seconds) and a component involving subvocal rehearsal—which maintains and refreshes information in the working memory. Neuroanatomically, the phonological loop is represented in the Brodmann area (BA) 40 in the parietal cortex and the rehearsal components in BA 44 and 6, both situated in the frontal cortex ( Osaka et al., 2007 ). The left inferior frontal gyrus (Broca’s area) and the left posterior superior temporal gyrus (Wernicke’s area) has been proposed to play a critical role in supporting phonological and verbal working memory tasks, specifically the subvocal rehearsal system of the articulatory loop ( Paulesu et al., 1993 ; Buchsbaum et al., 2001 ; Perrachione et al., 2017 ). The phonological store in verbal short-term memory has been localized at the left supramarginal gyrus ( Graves et al., 2008 ; Perrachione et al., 2017 ).

Studies utilizing neuroimaging techniques have consistently yielded results indicating notable activation in these brain regions during phonological activities like recalling non-words and maintaining verbal information in memory ( Awh et al., 1996 ; Graves et al., 2008 ). During tasks that require phonological rehearsal, there was an increase in activation in the left inferior frontal gyrus ( Paulesu et al., 1993 ). Researchers have noted an increase in activity within the superior temporal gyrus-which plays a significant role in auditory processing-in individuals performing tasks that necessitate verbal information maintenance and manipulation ( Smith et al., 1998 ; Chein et al., 2003 ).

Additionally, lesion studies have provided further confirmation regarding the importance of these regions. These investigations have revealed that impairment in performing phonological working memory tasks can transpire following damage inflicted upon the left hemisphere, particularly on perisylvian language areas ( Koenigs et al., 2011 ). It is common for individuals with lesions affecting regions associated with the phonological loop, such as the left inferior frontal gyrus and superior temporal gyrus, to have difficulty performing verbal working memory tasks. Clinical cases involving patients diagnosed with aphasia and specific language impairments have highlighted challenges related to retaining and manipulating auditory information. For example, those who sustain damage specifically within their left inferior frontal gyrus often struggle with tasks involving phonological rehearsal and verbal working memory activities, and therefore, they tend to perform poorly in tasks that require manipulation or repetition of verbal stimuli ( Saffran, 1997 ; Caplan and Waters, 2005 ).

The visuospatial sketchpad is engaged in the temporary retention and manipulation of visuospatial facts, including mental pictures, spatial associations, and object placements ( Miyake et al., 2001 ). The visuospatial sketchpad is localized to the right hemisphere, including the occipital lobe, parietal and frontal areas ( Osaka et al., 2007 ). Ren et al. (2019) identified the localization of the visuospatial sketchpad, and these areas were the right infero-lateral prefrontal cortex, lateral pre-motor cortices, right inferior parietal cortex, and the dorsolateral occipital cortices ( Burbaud et al., 1999 ; Salvato et al., 2021 ). Moreover, the posterior parietal cortex and the intraparietal sulcus have been implicated in spatial working memory ( Xu and Chun, 2006 ). Additionally, some evidence is available for an increase in brain regions associated with the visuospatial sketchpad during tasks involving mental imagery and spatial processing. Neuroimaging studies have revealed increased neural activation in some regions of the parietal cortex, mainly the superior and posterior parietal cortex, while performing mental rotation tasks ( Cohen et al., 1996 ; Kosslyn et al., 1997 ). However, further research is needed to better understand the visuospatial working memory and its integration with other cognitive processes ( Baddeley, 2003 ). Lesions to the regions involving the visuospatial sketchpad can have detrimental effects on visuospatial working memory tasks. Individuals with lesions to the posterior parietal cortex may exhibit deficits in mental rotation tasks and may be unable to mentally manipulate the visuospatial representation ( Buiatti et al., 2011 ). Moreover, studies concerning lesions have shown that damage to the parietal cortex can result in short-term deficits in visuospatial memory ( Shafritz et al., 2002 ). Damage to the occipital cortex can lead to performance impairments in tasks that require the generation and manipulation of mental visual images ( Moro et al., 2008 ).

The fourth component of the working memory, termed episodic buffer, was proposed by Baddeley (2000) . The episodic buffer is a multidimensional but essentially passive store that can hold a limited number of chunks, store bound features, and make them available to conscious awareness ( Baddeley et al., 2010 ; Hitch et al., 2019 ). Although research has suggested that episodic buffer is localized to the hippocampus ( Berlingeri et al., 2008 ) or the inferior lateral parietal cortex, it is thought to be not dependent on a single anatomical structure but instead can be influenced by the subsystems of working memory, long term memory, and even through perception ( Vilberg and Rugg, 2008 ; Baddeley et al., 2010 ). The episodic buffer provides a crucial link between the attentional central executive and the multidimensional information necessary for the operation of working memory ( Baddeley et al., 2011 ; Gelastopoulos et al., 2019 ).

The interdependence of the working memory modules, namely the phonological loop and visuospatial sketchpad, co-relates with other cognitive processes, for instance, spatial cognition and attention allocation ( Repovs and Baddeley, 2006 ). It has been found that the prefrontal cortex (PFC) and posterior parietal cortex (PPC) have a crucial role in several aspects of spatial cognition, such as the maintenance of spatially oriented attention and motor intentions ( Jerde and Curtis, 2013 ). The study by Sellers et al. (2016) and the review by Ikkai and Curtis (2011) posits that other brain areas could use the activity in PFC and PPC as a guide and manifest outputs to guide attention allocation, spatial memory, and motor planning. Moreover, research indicates that verbal information elicits an activation response in the left ventrolateral prefrontal cortex (VLPFC) when retained in the phonological loop, while visuospatial information is represented by a corresponding level of activity within the right homolog region ( Narayanan et al., 2005 ; Wolf et al., 2006 ; Emch et al., 2019 ). Specifically, the study by Yang et al. (2022) investigated the roles of two regions in the brain, the right inferior frontal gyrus (rIFG) and the right supra-marginal gyrus (rSMG), as they relate to spatial congruency in visual working memory tasks. A change detection task with online repetitive transcranial magnetic stimulation applied concurrently at both locations during high visual WM load conditions determined that rIFG is involved in actively repositioning the location of objects. At the same time, rSMG is engaged in passive perception of the stability of the location of objects.

Recent academic studies have found evidence to support the development of a new working memory model known as the state-based model ( D’Esposito and Postle, 2015 ). This theoretical model proposes that the allocation of attention toward internal representations permits short-term retention within working memory ( Ghaleh et al., 2019 ). The state-based model consists of two main categories: activated LTM models and sensorimotor recruitment models; the former largely focuses upon symbolic stimuli categorized under semantic aspects, while the latter has typically been applied to more perceptual tasks in experiments. This framework posits that prioritization through regulating cognitive processes provides insight into various characteristics across different activity types, including capacity limitations, proactive interference, etcetera ( D’Esposito and Postle, 2015 ). For example, the paper by Ghaleh et al. (2019) provides evidence for two separate mechanisms involved in maintenance of auditory information in verbal working memory: an articulatory rehearsal mechanism that relies more heavily on left sensorimotor areas and a non-articulatory maintenance mechanism that critically relies on left superior temporal gyrus (STG). These findings support the state-based model’s proposal that attentional allocation is necessary for short-term retention in working memory.

State-based models were found to be consistent with the suggested storage mechanism as they do not require representation transfer from one dedicated buffer type; research has demonstrated that any population of neurons and synapses may serve as such buffers ( Maass and Markram, 2002 ; Postle, 2006 ; Avraham et al., 2017 ). The review by D’Esposito and Postle (2015) examined the evidence to determine whether a persistent neural activity, synaptic mechanisms, or a combination thereof support representations maintained during working memory. Numerous neural mechanisms have been hypothesized to support the short-term retention of information in working memory and likely operate in parallel ( Sreenivasan et al., 2014 ; Kamiński and Rutishauser, 2019 ).

Persistent neural activity is the neural mechanism by which information is temporarily maintained ( Ikkai and Curtis, 2011 ; Panzeri et al., 2023 ). Recent review by Curtis and Sprague (2021) has focused on the notion that persistent neural activity is a fundamental mechanism for memory storage and have provided two main arcs of explanation. The first arc, mainly underpinned by empirical evidence from prefrontal cortex (PFC) neurophysiology experiments and computational models, posits that PFC neurons exhibit sustained firing during working memory tasks, enabling them to store representations in their active state ( Thuault et al., 2013 ). Intrinsic persistent firing in layer V neurons in the medial PFC has been shown to be regulated by HCN1 channels, which contribute to the executive function of the PFC during working memory episodes ( Thuault et al., 2013 ). Additionally, research has also found that persistent neural firing could possibly interact with theta periodic activity to sustain each other in the medial temporal, prefrontal, and parietal regions ( Düzel et al., 2010 ; Boran et al., 2019 ). The second arc involves advanced neuroimaging approaches which have, more recently, enabled researchers to decode content stored within working memories across distributed regions of the brain, including parts of the early visual cortex–thus extending this framework beyond just isolated cortical areas such as the PFC. There is evidence that suggests simple, stable, persistent activity among neurons in stimulus-selective populations may be a crucial mechanism for sustaining WM representations ( Mackey et al., 2016 ; Kamiński et al., 2017 ; Curtis and Sprague, 2021 ).

Badre (2008) discussed the functional organization of the PFC. The paper hypothesized that the rostro-caudal gradient of a function in PFC supported a control hierarchy, whereas posterior to anterior PFC mediated progressively abstract, higher-order controls ( Badre, 2008 ). However, this outlook proposed by Badre (2008) became outdated; the paper by Badre and Nee (2018) presented an updated look at the literature on hierarchical control. This paper supports neither a unitary model of lateral frontal function nor a unidimensional abstraction gradient. Instead, separate frontal networks interact via local and global hierarchical structures to support diverse task demands. This updated perspective is supported by recent studies on the hierarchical organization of representations within the lateral prefrontal cortex (LPFC) and the progressively rostral areas of the LPFC that process/represent increasingly abstract information, facilitating efficient and flexible cognition ( Thomas Yeo et al., 2011 ; Nee and D’Esposito, 2016 ). This structure allows the brain to access increasingly abstract action representations as required ( Nee and D’Esposito, 2016 ). It is supported by fMRI studies showing an anterior-to-posterior activation movement when tasks become more complex. Anatomical connectivity between areas also supports this theory, such as Area 10, which has projections back down to Area 6 but not vice versa.

Finally, studies confirm that different regions serve different roles along a hierarchy leading toward goal-directed behavior ( Badre and Nee, 2018 ). The paper by Postle (2015) exhibits evidence of activity in the prefrontal cortex that reflects the maintenance of high-level representations, which act as top-down signals, and steer the circulation of neural pathways across brain networks. The PFC is a source of top-down signals that influence processing in the posterior and subcortical regions ( Braver et al., 2008 ; Friedman and Robbins, 2022 ). These signals either enhance task-relevant information or suppress irrelevant stimuli, allowing for efficient yet effective search ( D’Esposito, 2007 ; D’Esposito and Postle, 2015 ; Kerzel and Burra, 2020 ). The study by Ratcliffe et al. (2022) provides evidence of the dynamic interplay between executive control mechanisms in the frontal cortex and stimulus representations held in posterior regions for working memory tasks. Moreover, the review by Herry and Johansen (2014) discusses the neural mechanisms behind actively maintaining task-relevant information in order for a person to carry out tasks and goals effectively. This review of data and research suggests that working memory is a multi-component system allowing for both the storage and processing of temporarily active representations. Neural activity throughout the brain can be differentially enhanced or suppressed based on context through top-down signals emanating from integrative areas such as PFC, parietal cortex, or hippocampus to actively maintain task-relevant information when it is not present in the environment ( Herry and Johansen, 2014 ; Kerzel and Burra, 2020 ).

In addition, Yu et al. (2022) examined how brain regions from the ventral stream pathway to the prefrontal cortex were activated during working memory (WM) gate opening and closing. They defined gate opening as the switch from maintenance to updating and gate closing as the switch from updating to maintenance. The data suggested that cognitive branching increases during the WM gating process, thus correlating the gating process and an information approach to the PFC function. The temporal cortices, lingual gyrus (BA19), superior frontal gyri including frontopolar cortices, and middle and inferior parietal regions are involved in processes of estimating whether a response option available will be helpful for each case. During gate closing, on the other hand, medial and superior frontal regions, which have been associated with conflict monitoring, come into play, as well as orbitofrontal and dorsolateral prefrontal processing at later times when decreasing activity resembling stopping or downregulating cognitive branching has occurred, confirming earlier theories about these areas being essential for estimation of usefulness already stored within long-term memories ( Yu et al., 2022 ).

Declarative and non-declarative memory

The distinctions between declarative and non-declarative memory are often based on the anatomical features of medial temporal lobe regions, specifically those involving the hippocampus ( Squire and Zola, 1996 ; Squire and Wixted, 2011 ). In the investigation of systems implicated in the process of learning and memory formation, it has been posited that the participation of the hippocampus is essential for the acquisition of declarative memories ( Eichenbaum and Cohen, 2014 ). In contrast, a comparatively reduced level of hippocampal involvement may suffice for non-declarative memories ( Squire and Zola, 1996 ; Williams, 2020 ).

Declarative memory (explicit) pertains to knowledge about facts and events. This type of information can be consciously retrieved with effort or spontaneously recollected without conscious intention ( Dew and Cabeza, 2011 ). There are two types of declarative memory: Episodic and Semantic. Episodic memory is associated with the recollection of personal experiences. It involves detailed information about events that happened in one’s life. Semantic memory refers to knowledge stored in the brain as facts, concepts, ideas, and objects; this includes language-related information like meanings of words and mathematical symbol values along with general world knowledge (e.g., capitals of countries) ( Binder and Desai, 2011 ). The difference between episodic and semantic memory is that when one retrieves episodic memory, the experience is known as “remembering”; when one retrieves information from semantic memory, the experience is known as “knowing” ( Tulving, 1985 ; Dew and Cabeza, 2011 ). The hippocampus, medial temporal lobe, and the areas in the diencephalon are implicated in declarative memory ( Richter-Levin and Akirav, 2003 ; Derner et al., 2020 ). The ventral parietal cortex (VPC) is involved in declarative memory processes, specifically episodic memory retrieval ( Henson et al., 1999 ; Davis et al., 2018 ). The evidence suggests that VPC and hippocampus is involved in the retrieval of contextual details, such as the location and timing of the event, and the information is critical for the formation of episodic memory ( Daselaar, 2009 ; Hutchinson et al., 2009 ; Wiltgen et al., 2010 ). The prefrontal cortex (PFC) is involved in the encoding (medial PFC) and retrieval (lateral PFC) of declarative memories, specifically in the integration of information across different sensory modalities ( Blumenfeld and Ranganath, 2007 ; Li et al., 2010 ). Research also suggests that the amygdala may modulate other brain regions involved with memory processing, thus, contributing to an enhanced recall of negative or positive experiences ( Hamann, 2001 ; Ritchey et al., 2008 ; Sendi et al., 2020 ). Maintenance of the integrity of hippocampal circuitry is essential for ensuring that episodic memory, along with spatial and temporal context information, can be retained in short-term or long-term working memory beyond 15 min ( Ito et al., 2003 ; Rasch and Born, 2013 ). Moreover, studies have suggested that the amygdala plays a vital role in encoding and retrieving explicit memories, particularly those related to emotionally charged stimuli which are supported by evidence of correlations between hippocampal activity and amygdala modulation during memory formation ( Richter-Levin and Akirav, 2003 ; Qasim et al., 2023 ).

Current findings in neuroimaging studies assert that a vast array of interconnected brain regions support semantic memory ( Binder and Desai, 2011 ). This network merges information sourced from multiple senses alongside different cognitive faculties necessary for generating abstract supramodal views on various topics stored within our consciousness. Modality-specific sensory, motor, and emotional system within these brain regions serve specialized tasks like language comprehension, while larger areas of the brain, such as the inferior parietal lobe and most of the temporal lobe, participate in more generalized interpretation tasks ( Binder and Desai, 2011 ; Kuhnke et al., 2020 ). These regions lie at convergences of multiple perceptual processing streams, enabling increasingly abstract, supramodal representations of perceptual experience that support a variety of conceptual functions, including object recognition, social cognition, language, and the remarkable human capacity to remember the past and imagine the future ( Binder and Desai, 2011 ; Binney et al., 2016 ). The following section will discuss the processes underlying memory consolidation and storage within declarative memory.

Non-declarative (implicit) memories refer to unconscious learning through experience, such as habits and skills formed from practice rather than memorizing facts; these are typically acquired slowly and automatically in response to sensory input associated with reward structures or prior exposure within our daily lives ( Kesner, 2017 ). Non-declarative memory is a collection of different phenomena with different neural substrates rather than a single coherent system ( Camina and Güell, 2017 ). It operates by similar principles, depending on local changes to a circumscribed brain region, and the representation of these changes is unavailable to awareness ( Reber, 2008 ). Non-declarative memory encompasses a heterogenous collection of abilities, such as associative learning, skills, and habits (procedural memory), priming, and non-associative learning ( Squire and Zola, 1996 ; Camina and Güell, 2017 ). Studies have concluded that procedural memory for motor skills depends upon activity in diverse set areas such as the motor cortex, striatum, limbic system, and cerebellum; similarly, perceptual skill learning is thought to be associated with sensory cortical activation ( Karni et al., 1998 ; Mayes, 2002 ). Research suggests that mutual connections between brain regions that are active together recruit special cells called associative memory cells ( Wang et al., 2016 ; Wang and Cui, 2018 ). These cells help integrate, store, and remember related information. When activated, these cells trigger the recall of memories, leading to behaviors and emotional responses. This suggests that co-activated brain regions with these mutual connections are where associative memories are formed ( Wang et al., 2016 ; Wang and Cui, 2018 ). Additionally, observational data reveals that priming mechanisms within distinct networks, such as the “repetition suppression” effect observed in visual cortical areas associated with sensory processing and in the prefrontal cortex for semantic priming, are believed to be responsible for certain forms of conditioning and implicit knowledge transfer experiences exhibited by individuals throughout their daily lives ( Reber, 2008 ; Wig et al., 2009 ; Camina and Güell, 2017 ). However, further research is needed to better understand the mechanisms of consolidation in non-declarative memory ( Camina and Güell, 2017 ).

The process of transforming memory into stable, long-lasting from a temporary, labile memory is known as memory consolidation ( McGaugh, 2000 ). Memory formation is based on the change in synaptic connections of neurons representing the memory. Encoding causes synaptic Long-Term potentiation (LTP) or Long-Term depression (LTD) and induces two consolidation processes. The first is synaptic or cellular consolidation which involves remodeling synapses to produce enduring changes. Cellular consolidation is a short-term process that involves stabilizing the neural trace shortly after learning via structural brain changes in the hippocampus ( Lynch, 2004 ). The second is system consolidation, which builds on synaptic consolidation where reverberating activity leads to redistribution for long-term storage ( Mednick et al., 2011 ; Squire et al., 2015 ). System consolidation is a long-term process during which memories are gradually transferred to and integrated with cortical neurons, thus promoting their stability over time. In this way, memories are rendered less susceptible to forgetting. Hebb postulated that when two neurons are repeatedly activated simultaneously, they become more likely to exhibit a coordinated firing pattern of activity in the future ( Langille, 2019 ). This proposed enduring change in synchronized neuronal activation was consequently termed cellular consolidation ( Bermudez-Rattoni, 2010 ).

The following sections of this paper incorporate a more comprehensive investigation into various essential procedures connected with memory consolidation- namely: long-term potentiation (LTP), long-term depression (LTD), system consolidation, and cellular consolidation. Although these mechanisms have been presented briefly before this paragraph, the paper aims to offer greater insight into each process’s function within the individual capacity and their collective contribution toward memory consolidation.

Synaptic plasticity mechanisms implicated in memory stabilization

Long-Term Potentiation (LTP) and Long-Term Depression (LTP) are mechanisms that have been implicated in memory stabilization. LTP is an increase in synaptic strength, whereas LTD is a decrease in synaptic strength ( Ivanco, 2015 ; Abraham et al., 2019 ).

Long-Term Potentiation (LTP) is a phenomenon wherein synaptic strength increases persistently due to brief exposures to high-frequency stimulation ( Lynch, 2004 ). Studies of Long-Term Potentiation (LTP) have led to an understanding of the mechanisms behind synaptic strengthening phenomena and have provided a basis for explaining how and why strong connections between neurons form over time in response to stimuli.

The NMDA receptor-dependent LTP is the most commonly described LTP ( Bliss and Collingridge, 1993 ; Luscher and Malenka, 2012 ). In this type of LTP, when there is high-frequency stimulation, the presynaptic neuron releases glutamate, an excitatory neurotransmitter. Glutamate binds to the AMPA receptor on the postsynaptic neuron, which causes the neuron to fire while opening the NMDA receptor channel. The opening of an NMDA channel elicits a calcium ion influx into the postsynaptic neuron, thus initiating a series of phosphorylation events as part of the ensuing molecular cascade. Autonomously phosphorylated CaMKII and PKC, both actively functional through such a process, have been demonstrated to increase the conductance of pre-existing AMPA receptors in synaptic networks. Additionally, this has been shown to stimulate the introduction of additional AMPA receptors into synapses ( Malenka and Nicoll, 1999 ; Lynch, 2004 ; Luscher and Malenka, 2012 ; Bailey et al., 2015 ).

There are two phases of LTP: the early phase and the late phase. It has been established that the early phase LTP (E-LTP) does not require RNA or protein synthesis; therefore, its synaptic strength will dissipate in minutes if late LTP does not stabilize it. On the contrary, late-phase LTP (L-LTP) can sustain itself over a more extended period, from several hours to multiple days, with gene transcription and protein synthesis in the postsynaptic cell ( Frey and Morris, 1998 ; Orsini and Maren, 2012 ). The strength of presynaptic tetanic stimulation has been demonstrated to be a necessary condition for the activation of processes leading to late LTP ( Luscher and Malenka, 2012 ; Bailey et al., 2015 ). This finding is supported by research examining synaptic plasticity, notably Eric Kandel’s discovery that CREB–a transcription factor–among other cytoplasmic and nuclear molecules, are vital components in mediating molecular changes culminating in protein synthesis during this process ( Kaleem et al., 2011 ; Kandel et al., 2014 ). Further studies have shown how these shifts ultimately lead to AMPA receptor stabilization at post-synapses facilitating long-term potentiation within neurons ( Luscher and Malenka, 2012 ; Bailey et al., 2015 ).

The “synaptic tagging and capture hypothesis” explains how a weak event of tetanization at synapse A can transform to late-LTP if followed shortly by the strong tetanization of a different, nearby synapse on the same neuron ( Frey and Morris, 1998 ; Redondo and Morris, 2011 ; Okuda et al., 2020 ; Park et al., 2021 ). During this process, critical plasticity-related proteins (PRPs) are synthesized, which stabilize their own “tag” and that from the weaker synaptic activity ( Moncada et al., 2015 ). Recent evidence suggests that calcium-permeable AMPA receptors (CP-AMPARs) are involved in this form of heterosynaptic metaplasticity ( Park et al., 2018 ). The authors propose that the synaptic activation of CP-AMPARs triggers the synthesis of PRPs, which are then engaged by the weak induction protocol to facilitate LTP on the independent input. The paper also suggests that CP-AMPARs are required during the induction of LTP by the weak input for the full heterosynaptic metaplastic effect to be observed ( Park et al., 2021 ). Additionally, it has been further established that catecholamines such as dopamine plays an integral part in memory persistence by inducing PRP synthesis ( Redondo and Morris, 2011 ; Vishnoi et al., 2018 ). Studies have found that dopamine release in the hippocampus can enhance LTP and improve memory consolidation ( Lisman and Grace, 2005 ; Speranza et al., 2021 ).

Investigations into neuronal plasticity have indicated that synaptic strength alterations associated with certain forms of learning and memory may be analogous to those underlying Long-Term Potentiation (LTP). Research has corroborated this notion, demonstrating a correlation between these two phenomena ( Lynch, 2004 ). The three essential properties of Long-Term Potentiation (LTP) that have been identified are associativity, synapse specificity, and cooperativity ( Kandel and Mack, 2013 ). These characteristics provide empirical evidence for the potential role of LTP in memory formation processes. Specifically, associativity denotes the amplification of connections when weak stimulus input is paired with a powerful one; synapse specificity posits that this potentiating effect only manifests on synaptic locations exhibiting coincidental activity within postsynaptic neurons, while cooperativity suggests stimulated neuron needs to attain an adequate threshold of depolarization before LTP can be induced again ( Orsini and Maren, 2012 ).

There is support for the idea that memories are encoded by modification of synaptic strengths through cellular mechanisms such as LTP and LTD ( Nabavi et al., 2014 ). The paper by Nabavi et al. (2014) shows that fear conditioning, a type of associative memory, can be inactivated and reactivated by LTD and LTP, respectively. The findings of the paper support a causal link between these synaptic processes and memory. Moreover, the paper suggests that LTP is used to form neuronal assemblies that represent a memory, and LTD could be used to disassemble them and thereby inactivate a memory ( Nabavi et al., 2014 ). Hippocampal LTD has been found to play an essential function in regulating synaptic strength and forming memories, such as long-term spatial memory ( Ge et al., 2010 ). However, it is vital to bear in mind that studies carried out on LTP exceed those done on LTD; hence the literature on it needs to be more extensive ( Malenka and Bear, 2004 ; Nabavi et al., 2014 ).

Cellular consolidation and memory

For an event to be remembered, it must form physical connections between neurons in the brain, which creates a “memory trace.” This memory trace can then be stored as long-term memory ( Langille and Brown, 2018 ). The formation of a memory engram is an intricate process requiring neuronal depolarization and the influx of intracellular calcium ( Mank and Griesbeck, 2008 ; Josselyn et al., 2015 ; Xu et al., 2017 ). This initiation leads to a cascade involving protein transcription, structural and functional changes in neural networks, and stabilization during the quiescence period, followed by complete consolidation for its success. Interference from new learning events or disruption caused due to inhibition can abort this cycle leading to incomplete consolidation ( Josselyn et al., 2015 ).

Cyclic-AMP response element binding protein (CREB) has been identified as an essential transcription factor for memory formation ( Orsini and Maren, 2012 ). It regulates the expression of PRPs and enhances neuronal excitability and plasticity, resulting in changes to the structure of cells, including the growth of dendritic spines and new synaptic connections. Blockage or enhancement of CREB in certain areas can affect subsequent consolidation at a systems level–decreasing it prevents this from occurring, while aiding its presence allows even weak learning conditions to produce successful memory formation ( Orsini and Maren, 2012 ; Kandel et al., 2014 ).

Strengthening weakly encoded memories through the synaptic tagging and capture hypothesis may play an essential role in cellular consolidation. Retroactive memory enhancement has also been demonstrated in human studies, mainly when items are initially encoded with low strength but later paired with shock after consolidation ( Dunsmoor et al., 2015 ). The synaptic tagging and capture theory (STC) and its extension, the behavioral tagging hypothesis (BT), have both been used to explain synaptic specificity and the persistence of plasticity ( Moncada et al., 2015 ). STC proposed that electrophysiological activity can induce long-term changes in synapses, while BT postulates similar effects of behaviorally relevant neuronal events on learning and memory models. This hypothesis proposes that memory consolidation relies on combining two distinct processes: setting a “learning tag” and synthesizing plasticity-related proteins ( De novo protein synthesis, increased CREB levels, and substantial inputs to nearby synapses) at those tagged sites. BT explains how it is possible for event episodes with low-strength inputs or engagements can be converted into lasting memories ( Lynch, 2004 ; Moncada et al., 2015 ). Similarly, the emotional tagging hypothesis posits that the activation of the amygdala in emotionally arousing events helps to mark experiences as necessary, thus enhancing synaptic plasticity and facilitating transformation from transient into more permanent forms for encoding long-term memories ( Richter-Levin and Akirav, 2003 ; Zhu et al., 2022 ).

Cellular consolidation, the protein synthesis-dependent processes observed in rodents that may underlie memory formation and stabilization, has been challenging to characterize in humans due to the limited ability to study it directly ( Bermudez-Rattoni, 2010 ). Additionally, multi-trial learning protocols commonly used within human tests as opposed to single-trial experiments conducted with non-human subjects suggest there could be interference from subsequent information that impedes individual memories from being consolidated reliably. This raises important questions regarding how individuals can still form strong and long-lasting memories when exposed to frequent stimuli outside controlled laboratory conditions. Although this phenomenon remains undiscovered by science, it is of utmost significance for gaining a deeper understanding of our neural capacities ( Genzel and Wixted, 2017 ).

The establishment of distributed memory traces requires a narrow temporal window following the initial encoding process, during which cellular consolidation occurs ( Nader and Hardt, 2009 ). Once this period ends and consolidation has been completed, further protein synthesis inhibition or pharmacological disruption will be less effective at altering pre-existing memories and interfering with new learning due to the stabilization of the trace in its new neuronal network connections ( Nader and Hardt, 2009 ). Thus, systems consolidation appears critical for the long-term maintenance of memory within broader brain networks over extended periods after their formation ( Bermudez-Rattoni, 2010 ).

System consolidation and memory

Information is initially stored in both the hippocampus and neocortex ( Dudai et al., 2015 ). The hippocampus subsequently guides a gradual process of reorganization and stabilization whereby information present within the neocortex becomes autonomous from that in the hippocampal store. Scholars have termed this phenomenon “standard memory consolidation model” or “system consolidation” ( Squire et al., 2015 ).

The Standard Model suggests that information acquired during learning is simultaneously stored in both the hippocampus and multiple cortical modules. Subsequently, it posits that over a period of time which may range from weeks to months or longer, the hippocampal formation directs an integration process by which these various elements become enclosed into single unified structures within the cortex ( Gilboa and Moscovitch, 2021 ; Howard et al., 2022 ). These newly learned memories are then assimilated into existing networks without interference or compression when necessary ( Frankland and Bontempi, 2005 ). It is important to note that memory engrams already exist within cortical networks during encoding. They only need strengthening through links enabled by hippocampal assistance-overtime allowing remote memory storage without reliance on the latter structure. Data appears consistent across studies indicating that both AMPA-and NMDA receptor-dependent “tagging” processes occurring within the cortex are essential components of progressive rewiring, thus enabling longer-term retention ( Takeuchi et al., 2014 ; Takehara-Nishiuchi, 2020 ).

Recent studies have additionally demonstrated that the rate of system consolidation depends on an individual’s ability to relate new information to existing networks made up of connected neurons, popularly known as “schemas” ( Robin and Moscovitch, 2017 ). In situations where prior knowledge is present and cortical modules are already connected at the outset of learning, it has been observed that a hippocampal-neocortical binding process occurs similarly to when forming new memories ( Schlichting and Preston, 2015 ). The proposed framework involves the medial temporal lobe (MTL), which is involved in acquiring new information and binds different aspects of an experience into a single memory trace. In contrast, the medial prefrontal cortex (mPFC) integrates this information with the existing knowledge ( Zeithamova and Preston, 2010 ; van Kesteren et al., 2012 ). During consolidation and retrieval, MTL is involved in replaying memories to the neocortex, where they are gradually integrated with existing knowledge and schemas and help retrieve memory traces. During retrieval, the mPFC is thought to use existing knowledge and schemas to guide retrieval and interpretation of memory. This may involve the assimilation of newly acquired information into existing cognitive schemata as opposed to the comparatively slow progression of creating intercortical connections ( Zeithamova and Preston, 2010 ; van Kesteren et al., 2012 , 2016 ).

Medial temporal lobe structures are essential for acquiring new information and necessary for autobiographical (episodic) memory ( Brown et al., 2018 ). The consolidation of autobiographical memories depends on a distributed network of cortical regions. Brain areas such as entorhinal, perirhinal, and parahippocampal cortices are essential for learning new information; however, they have little impact on the recollection of the past ( Squire et al., 2015 ). The hippocampus is a region of the brain that forms episodic memories by linking multiple events to create meaningful experiences ( Cooper and Ritchey, 2019 ). It receives information from all areas of the association cortex and cingulate cortex, subcortical regions via the fornix, as well as signals originating within its entorhinal cortex (EC) and amygdala regarding emotionally laden or potentially hazardous stimuli ( Sorensen, 2009 ). Such widespread connectivity facilitates the construction of an accurate narrative underpinning each remembered episode, transforming short-term into long-term recollections ( Richter-Levin and Akirav, 2003 ).

Researchers have yet to establish a consensus regarding where semantic memory information is localized within the brain ( Roldan-Valadez et al., 2012 ). Some proponents contend that such knowledge is lodged within perceptual and motor systems, triggered when we initially associate with a given object. This point of view is supported by studies highlighting how neural activity occurs initially in the occipital cortex, followed by left temporal lobe involvement during processing and pertinent contributions to word selection/retrieval via activation of left inferior frontal cortices ( Patterson et al., 2007 ). Moreover, research indicates elevated levels of fusiform gyrus engagement (a ventral surface region encompassing both temporal lobes) occurring concomitantly with verbal comprehension initiatives, including reading and naming tasks ( Patterson et al., 2007 ).

Research suggests that the hippocampus is needed for a few years after learning to support semantic memory (factual information), yet, it is not needed for the long term ( Squire et al., 2015 ). However, some forms of memory remain dependent on the hippocampus, such as the retrieval of spatial memory ( Wiltgen et al., 2010 ). Similarly, the Multiple-trace theory ( Moscovitch et al., 2006 ), also known as the transformation hypothesis ( Winocur and Moscovitch, 2011 ), posits that hippocampal engagement is necessary for memories that retain contextual detail such as episodic memories. Consolidation of memories into the neocortex is theorized to involve a loss of specific finer details, such as temporal and spatial information, in addition to contextual elements. This transition ultimately results in an evolution from episodic memory toward semantic memory, which consists mainly of gist-based facts ( Moscovitch et al., 2006 ).

Sleep and memory consolidation

Sleep is an essential physiological process crucial to memory consolidation ( Siegel, 2001 ). Sleep is divided into two stages: Non-rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. NREM sleep is divided into three stages: N1, N2, and N3 (AKA Slow Wave Sleep or SWS) ( Rasch and Born, 2013 ). Each stage displays unique oscillatory patterns and phenomena responsible for consolidating memories in distinct ways. The first stage, or N1 sleep, is when an individual transitions between wakefulness and sleep. This type of sleep is characterized by low-amplitude, mixed-frequency brain activity. N1 sleep is responsible for the initial encoding of memories ( Rasch and Born, 2013 ). The second stage, or N2 sleep, is characterized by the occurrence of distinct sleep spindles and K-complexes in EEG. N2 is responsible for the consolidation of declarative memories ( Marshall and Born, 2007 ). The third stage of sleep N3, also known as slow wave sleep (SWS), is characterized by low-frequency brain activity, slow oscillations, and high amplitude. The slow oscillations which define the deepest stage of sleep are trademark rhythms of NREM sleep. These slow oscillations are delta waves combined to indicate slow wave activity (SWA), which is implicated in memory consolidation ( Tononi and Cirelli, 2003 ; Stickgold, 2005 ; Kim et al., 2019 ). Sleep spindles are another trademark defining NREM sleep ( Stickgold, 2005 ). Ripples are high-frequency bursts, and when combined with irregularly occurring sharp waves (high amplitude), they form the sharp-wave ripple (SWR). These spindles and the SWRs coordinate the reactivation and redistribution of hippocampus-dependent memories to neocortical sites ( Ngo et al., 2020 ; Girardeau and Lopes-dos-Santos, 2021 ). The third stage is also responsible for the consolidation of procedural memories, such as habits and motor skills ( Diekelmann and Born, 2010 ). During SWS, there is minimal cholinergic activity and intermediate noradrenergic activity ( Datta and MacLean, 2007 ).

Finally, the fourth stage of sleep is REM sleep, characterized by phasic REMs and muscle atonia ( Reyes-Resina et al., 2021 ). During REM sleep, there is high cholinergic activity, serotonergic and noradrenergic activity are at a minimum, and high theta activity ( Datta and MacLean, 2007 ). REM sleep is also characterized by local increases in plasticity-related immediate-early gene activity, which might favor the subsequent synaptic consolidation of memories in the cortex ( Ribeiro, 2007 ; Diekelmann and Born, 2010 ; Reyes-Resina et al., 2021 ). The fourth stage of sleep is responsible for the consolidation of emotional memories and the integration of newly acquired memories into existing knowledge structures ( Rasch and Born, 2013 ). Studies indicate that the cholinergic system plays an imperative role in modifying these processes by toggling the entire thalamo-cortico-hippocampal network between distinct modes, namely high Ach encoding mode during active wakefulness and REM sleep and low Ach consolidation mode during quiet wakefulness and NREM sleep ( Bergmann and Staresina, 2017 ; Li et al., 2020 ). Consequently, improving neocortical hippocampal communication results in efficient memory encoding/synaptic plasticity, whereas hippocampo-neocortical interactions favor better systemic memory consolidation ( Diekelmann and Born, 2010 ).

The dual process hypothesis of memory consolidation posits that SWS facilitates declarative, hippocampus-dependent memory, whereas REM sleep facilitates non-declarative hippocampus-independent memory ( Maquet, 2001 ; Diekelmann and Born, 2010 ). On the other hand, the sequential hypothesis states that different sleep stages play a sequential role in memory consolidation. Memories are encoded during wakefulness, consolidated during NREM sleep, and further processed and integrated during REM sleep ( Rasch and Born, 2013 ). However, there is evidence present that contradicts the sequential hypothesis. A study by Goerke et al. (2013) found that declarative memories can be consolidated during REM sleep, suggesting that the relationship between sleep stages and memory consolidation is much more complex than a sequential model. Moreover, other studies indicate the importance of coordinating specific sleep phases with learning moments for optimal memory retention. This indicates that the timing of sleep has more influence than the specific sleep stages ( Gais et al., 2006 ). The active system consolidation theory suggests that an active consolidation process results from the selective reactivation of memories during sleep; the brain selectively reactivates newly encoded memories during sleep, which enhances and integrates them into the network of pre-existing long-term memories ( Born et al., 2006 ; Howard et al., 2022 ). Research has suggested that slow-wave sleep (SWS) and rapid eye movement (REM) sleep have complementary roles in memory consolidation. Declarative and non-declarative memories benefiting differently depending on which sleep stage they rely on ( Bergmann and Staresina, 2017 ). Specifically, during SWS, the brain actively reactivates and reorganizes hippocampo-neocortical memory traces as part of system consolidation. Following this, REM sleep is crucial for stabilizing these reactivated memory traces through synaptic consolidation. While SWS may initiate early plastic processes in hippocampo-neocortical memory traces by “tagging” relevant neocortico-neocortical synapses for later consolidation ( Frey and Morris, 1998 ), long-term plasticity requires subsequent REM sleep ( Rasch and Born, 2007 , 2013 ).

The active system consolidation hypothesis is not the only mechanism proposed for memory consolidation during sleep. The synaptic homeostasis hypothesis proposes that sleep is necessary for restoring synaptic homeostasis, which is challenged by synaptic strengthening triggered by learning during wake and synaptogenesis during development ( Tononi and Cirelli, 2014 ). The synaptic homeostasis hypothesis assumes consolidation is a by-product of the global synaptic downscaling during sleep ( Puentes-Mestril and Aton, 2017 ). The two models are not mutually exclusive, and the hypothesized processes probably act in concert to optimize the memory function of sleep ( Diekelmann and Born, 2010 ).

Non-rapid eye movement sleep plays an essential role in the systems consolidation of memories, with evidence showing that different oscillations are involved in this process ( Düzel et al., 2010 ). With an oscillatory sequence initiated by a slow frontal cortex oscillation (0.5–1 Hz) traveling to the medial temporal lobe and followed by a sharp-wave ripple (SWR) in the hippocampus (100–200 Hz). Replay activity of memories can be measured during this oscillatory sequence across various regions, including the motor cortex and visual cortex ( Ji and Wilson, 2006 ; Eichenlaub et al., 2020 ). Replay activity of memory refers to the phenomenon where the hippocampus replays previously experienced events during sharp wave ripples (SWRs) and theta oscillations ( Zielinski et al., 2018 ). During SWRs, short, transient bursts of high-frequency oscillations occur in the hippocampus. During theta oscillations, hippocampal spikes are ordered according to the locations of their place fields during behavior. These sequential activities are thought to play a role in memory consolidation and retrieval ( Zielinski et al., 2018 ). The paper by Zielinski et al. (2018) suggests that coordinated hippocampal-prefrontal representations during replay and theta sequences play complementary and overlapping roles at different stages in learning, supporting memory encoding and retrieval, deliberative decision-making, planning, and guiding future actions.

Additionally, the high-frequency oscillations of SWR reactivate groups of neurons attributed to spatial information encoding to align synchronized activity across an array of neural structures, which results in distributed memory creation ( Swanson et al., 2020 ; Girardeau and Lopes-dos-Santos, 2021 ). Parallel to this process is slow oscillation or slow-wave activity within cortical regions, which reflects synced neural firing and allows regulation of synaptic weights, which is in accordance with the synaptic homeostasis hypothesis (SHY). The SHY posits that downscaling synaptic strengths help incorporate new memories by avoiding saturation of resources during extended periods–features validated by discoveries where prolonged wakefulness boosts amplitude while it diminishes during stretches of enhanced sleep ( Girardeau and Lopes-dos-Santos, 2021 ).

During REM sleep, the brain experiences “paradoxical” sleep due to the similarity in activity to wakefulness. This stage plays a significant role in memory processing. Theta oscillations which are dominant during REM sleep, are primarily observed in the hippocampus, and these are involved in memory consolidation ( Landmann et al., 2014 ). There has been evidence of coherence between theta oscillations in the hippocampus, medial frontal cortex, and amygdala, which support their involvement in memory consolidation ( Popa et al., 2010 ). During REM sleep, phasic events such as ponto-geniculo-occipital waves originating from the brainstem coordinate activity across various brain structures and may contribute to memory consolidation processes ( Rasch and Born, 2013 ). Research has suggested that sleep-associated consolidation may be mediated by the degree of overlap between new and already known material whereby, if the acquired information is similar to the information one has learned, it is more easily consolidated during sleep ( Tamminen et al., 2010 ; Sobczak, 2017 ).

In conclusion, understanding more about how the brains cycle through different stages of sleep, including specific wave patterns, offers valuable insight into the ability to store memories effectively. While NREM sleep is associated with SWRs and slow oscillations, facilitating memory consolidation and synaptic downscaling, REM sleep, characterized by theta oscillations and phasic events, contributes to memory reconsolidation and the coordination of activity across brain regions. By exploring the interactions between sleep stages, oscillations, and memory processes, one may learn more about how sleep impacts brain function and cognition in greater detail.

Century has passed since we addressed memory, and several notable findings have moved from bench-to-bedside research. Several cross-talks between multidiscipline have been encouraged. Nevertheless, further research is needed into neurobiological mechanisms of non-declarative memory, such as conditioning ( Gallistel and Balsam, 2014 ). Modern research indicates that structural change that encodes information is likely at the level of the synapse, and the computational mechanisms are implemented at the level of neural circuitry. However, it also suggests that intracellular mechanisms realized at the molecular level, such as micro RNAs, should not be discounted as potential mechanisms. However, further research is needed to study the molecular and structural changes brought on by implicit memory ( Gallistel and Balsam, 2014 ).

The contribution of non-human animal studies toward our understanding of memory processes cannot be understated; hence recognizing their value is vital for moving forward. While this paper predominantly focused on cognitive neuroscience perspectives, some articles cited within this paper were sourced from non-human animal studies providing fundamental groundwork and identification of critical mechanisms relevant to human memories. A need persists for further investigation—primarily with humans—which can validate existing findings from non-human animals. Moving forward, it is prudent for researchers to bridge the gap between animal and human investigations done while exploring parallels and exploring unique aspects of human memory processes. By integrating findings from both domains, one can gain a more comprehensive understanding of the complexities of memory and its underlying neural mechanisms. Such investigations will broaden the horizon of our memory process and answer the complex nature of memory storage.

This paper attempted to provide an overview and summarize memory and its processes. The paper focused on bringing the cognitive neuroscience perspective on memory and its processes. This may provide the readers with the understanding, limitations, and research perspectives of memory mechanisms.

Data availability statement

Author contributions.

SS and MKA: conceptualization, framework, and manuscript writing. AK: review and editing of the manuscript. All authors contributed to the article and approved the submitted version.

Acknowledgments

We gratefully thank students and Indian Institute of Technology Roorkee (IITR) office staff for their conditional and unconditional support. We also thank the Memory and Anxiety Research Group (MARG), IIT Roorkee for its constant support.

Funding Statement

MKA was supported by the F.I.G. grant (IITR/SRIC/2741). The funding agency had no role in the preparation of the manuscript.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

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The 3 Major Types of Memory And Every Subtype: A Complete Guide

Anthony Metivier | April 11, 2023 | Memory

If you search the Internet you can actually find a variety of answers.

But is it three, four, five, or more? 

And if you find the correct number, how many can you improve?

You are not alone. 

The confusion is understandable because memory science is a complex and ever-evolving field. 

In fact, there are a number of models of memory types that experts and academics have proposed over the years. As you can see from this infographic, the types of memory are also laid out differently by different disciplines:

Whereas biology and psychology describe different kinds of memory models with particular kinds of terminology, social and cultural studies have words and terms of their own. Both fields also progress and often add or change terms as more research is carried out. 

These are just some of the reasons why so much terminology abounds.

So with this background in mind, what are the main different types of memory? The kinds you really need to know.

The Three Main Types of Human Memory

In this post, we will cover the 3 principal types of human memory as our key guides into this world of learning and remembering:

• Sensory memory
• Short-term memory
• Long-term memory

You’ll see how these three types of memory can be broken down further into various constituent parts. 

Combined, these parts form what you might think of as a ‘memory orchestra’ – an array of memory types our brains use to help us navigate the world. 

These three kinds of memory are also the basis for the three-stage or multi-store model of memory proposed by Atkinson and Shiffrin in 1968. It is still the most agreed upon memory model in science and has been further developed by other academics. 

It basically looks like this, starting with the information encountered by your sensory memory:

This infographic is one way of representing the three-stage or multi-store model of memory first proposed by Atkinson and Shiffrin in 1968.

• Sensory (iconic, haptic, echoic, olfactory, and gustatory)
• Short-term (includes working memory)
• Long-term – explicit (includes declarative, episodic and semantic) and implicit memory (includes procedural)

As you can see, these three memory types serve as umbrella terms for various other kinds of memory. By the end of the article, you will have learnt about the various types of memory and how this knowledge can help your memory powers! 

Let’s get started with the first type of memory we all rely upon first and foremost.

One: Sensory Memory

This type of human memory derives directly from the five senses. 

These senses are often experienced within a few seconds or can last for minutes. 

George Sperling , a cognitive psychologist working in the 1960s, did important work which established just how short sensory memories are. He found that most of our sensory memories are gone within a quarter of a second. 

Even though momentary, all memories we ever retain start here and come from your sight, smell, touch, taste, or from what you hear. Here are the names for the specific types of memory.

Sensory memory breaks down into a number of sub-categories.

Sensory memory involves at least these five modes of sensory perception.

Iconic – relating to our visual experiences

Echoic – relating sounds we hear.

Haptic – relating to touch

Olfactory – relating to smell

Gustatory – relating to taste

Needless to say, the more senses that are engaged, the more memorable the input. As a consequence, the more likely the information is to remain in longer-term memory. 

If you want to guarantee that your sensory memory works better, try these tutorials:

• Elaborative encoding exercises
• Sensory memory exercises

Two: Short-term Memory

Having passed through our sensory memory, information then travels to our short-term memories. 

Like sensory memories, we hold new memories for a very short period – usually up to 30 seconds. 

George Miller covered this kind of memory in his classic 1956 study, “The magical number seven, plus or minus two: Some limits on our capacity for processing information.”  

This study is well known for stating that we have 5 to 9 slots available in our short-term memories. All of our memories pass through this stage and they are either discarded as they are not needed for long, or they get retained and passed into longer-term memory stores.

Of course, memory athletes break this rule all the time. And you can too.

Working Memory

Remember the last time you tried to remember a list of words or a phone number but did not have a pen and paper? This would be using working memory. 

Often used interchangeably with short-term memory, this is the form of memory dedicated to performing certain tasks. For example, remembering an internet password, a phone number, or a short shopping list.

Without rehearsal, memories in this area are not retained for long. If some of these working memories are useful for a longer period, it might be worth committing them to long-term memory which is the next type of memory we will turn to.

Three: Long-term Memory

This form of memory is for longer-term storage and has unlimited capacity. 

In The Brain: The Story of You (2016) , David Eagleman says we have a zettabyte of memory at our disposal. This is considered enough to store approximately 30% of all the information in the world. 

Whilst you may never need to remember that much, this is the kind of memory people usually would like to improve. We may broadly divide the kinds of long-term memory into explicit memory involving conscious thought, and implicit memory which involves unconscious thought.

Explicit Memory

This type of memory recalls specific events and recollections from the past and has three elements to it:

Declarative Memory

This is the recall of facts and snippets of memory that take conscious effort to remember. Whenever you were preparing for a test, you were working on improving your declarative memory and your ability to recall those particular facts. Declarative Memory is further divided into two related parts – episodic and semantic memory. They often work in harmony such as when recalling autobiographical details about your life.

• Episodic Memory

As the word suggests, this kind of long-term memory relates to episodes – brief snippets from your life – and their recall. These memories are all the stronger if they are associated with emotions whether good or bad. You may never forget being bitten by a dog, or the way you felt the day you got a shiny bike for Christmas. We can also include autobiographical memory here – we can all relate to moments in our lives or stories that we have recalled multiple times that we can ‘declare’. These are also sometimes called experiential memories.

Semantic Memory

This is the body of knowledge stored in our brains that helps us understand and describe the world. For example, knowing what a dog is, how many days are there in each month, knowing that the sea is blue, the grass is green and so on. 

Facts you can draw from memory include the colors of things like grass and water. You might even know the names for these objects in multiple languages.

These types of long-term memories represent our general knowledge about the world – facts. As the word suggests, these memories are the essential building blocks that provide the context and the meaning in our lives. They are stored away in our brains for retrieval. 

For example, if you are recalling your wedding day (an episodic memory ) you need to have the key building blocks for the story – the color of the bride’s dress, the type of car, the church, the guests, the speeches, the weather and so on. This is an illustration of how episodic memories and semantic memories are often used together.

Implicit Memory

The other major category inside long-term memory is implicit memory. This is a kind of memory that does not have to be consciously recalled and can affect thoughts and behaviors. These memories become automatic after an initial period of exposure, study and practice . Studies have been done, for example, around how strongly people associate the melodies and words in a song. If you play the same melody with different words, people often say they don’t know it. Implicit memory often involves the brain making associations between two types of inputs in this way.

Procedural Memory

This is often the most highlighted element inside the implicit memory category. This kind of long-term memory relates to carrying out a certain task or list of tasks. 

For example, many of us would have learnt to ride a bike or drive a car. After initially learning, then consciously doing and then repeating, we no longer have to make a conscious effort to carry out these tasks. 

Riding a bike draws strongly upon your procedural memory.

Indeed, it is often possible to carry out another unrelated activity whilst carrying out these kinds of tasks. For example, you can sing along with your favorite song while driving your car. 

Procedural memory usually involves knowledge that gets stronger primarily through repetition and feedback. These are the types of memories that high-level performers in sports or other fields are trying to cultivate. A golfer cannot consciously remember every single movement in his swing when trying to hit the ball. He has to practice the movement and get feedback until the movement becomes unconscious and the memories therein are implicit.

Improving your memory

As we’ve seen, there are primarily three stages of memory. Another way of describing them is to call them:

Encoding can be done via the senses, storage is either short-term or long term and retrieval involves both short-term and long term memory. See here for some further discussion on the stages of memory.

Now, when people talk about improving our memories they are generally thinking about improving retrieval. However, we need to treat memory improvement holistically and improve all three levels.

With that in mind, what does understanding the types of memory mean for improving all of these levels?

Mnemonic devices

Devices such as these help recall by giving the brain a simple accessible framework to use. Everybody remembers things such as Every Good Boy Deserves Fruit to remember the names for musical notes that fall on the lines on a stave. These are used extensively in many fields to remember certain facts and naturally, you can invent your own.

Testing and The Rehearsal Loop

It is something that our teachers used with us at school but worth remembering. The act of repeatedly retrieving memories has a greater impact than long study periods. When you have something you are trying to retain in your short-term memory you are advised to use a rehearsal loop to keep the memories fresh. Over an extended time, using rehearsal and testing, memories can find their way into long-term memory. If these activities can be turned into games to make them more fun, the results are certain to be better.

Immediate Feedback

Immediate feedback creates better long term memories too. When undertaking any activity, and this applies particularly to learning a skill, it is ideal to have immediate feedback so you can correct your faults and then practice the skill correctly. There is nothing worse than remembering the wrong way to do something! 

Sleep and Health

Sleep works as a cleansing system that reduces the presence of toxins and improves brain function. Those who sacrifice sleep are likely to see a build-up of metabolic toxins such as the sticky protein beta-amyloid. Naturally, minimizing stress, eating well, and exercise all have great impacts on the brain and its memory function.

Some coffee

Research has shown that a certain quantity of coffee can improve our mental sharpness but too much has the opposite effect.

Play Brain Games and Have Fun

As with muscles in the body, the more you use them the stronger they get. Brain games or anything that exercises the grey matter can have a positive benefit on overall memory performance.

The study of the brain continues and new discoveries bring slight changes to the theories. Our memories are immensely powerful and have unlimited capacities. With a deeper understanding of the brain’s user manual and the types of memory stored therein, we can get more from our memories and an accompanying positive impact on our lives. 

To maximize the impact, consider signing up for my Free Memory Improvement Kit. In just a few days, you can experience tremendous boosts in your memory, and have fun while doing it.

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Chapter 9. Remembering and Judging

9.1 Memories as Types and Stages

Learning objectives.

• Compare and contrast explicit and implicit memory, identifying the features that define each.
• Explain the function and duration of eidetic and echoic memories.
• Summarize the capacities of short-term memory and explain how working memory is used to process information in it.

As you can see in Table 9.1, “Memory Conceptualized in Terms of Types, Stages, and Processes,” psychologists conceptualize memory in terms of types , in terms of stages , and in terms of processes . In this section we will consider the two types of memory , explicit memory and implicit memory , and then the three major memory stages : sensory , short-term , and long-term (Atkinson & Shiffrin, 1968). Then, in the next section, we will consider the nature of long-term memory, with a particular emphasis on the cognitive techniques we can use to improve our memories. Our discussion will focus on the three processes that are central to long-term memory : encoding , storage , and retrieval .

Explicit Memory

When we assess memory by asking a person to consciously remember things, we are measuring explicit memory . Explicit memory  refers to knowledge or experiences that can be consciously remembered . As you can see in Figure 9.2, “Types of Memory,” there are two types of explicit memory: episodic and semantic . Episodic memory refers to the firsthand experiences that we have had (e.g., recollections of our high school graduation day or of the fantastic dinner we had in New York last year). Semantic memory refers to our knowledge of facts and concepts about the world (e.g., that the absolute value of −90 is greater than the absolute value of 9 and that one definition of the word “affect” is “the experience of feeling or emotion”).

Explicit memory is assessed using measures in which the individual being tested must consciously attempt to remember the information. A recall memory test is a measure of explicit memory that involves bringing from memory information that has previously been remembered . We rely on our recall memory when we take an essay test, because the test requires us to generate previously remembered information. A multiple-choice test is an example of a recognition memory test , a measure of explicit memory that involves determining whether information has been seen or learned before .

Your own experiences taking tests will probably lead you to agree with the scientific research finding that recall is more difficult than recognition. Recall, such as required on essay tests, involves two steps: first generating an answer and then determining whether it seems to be the correct one. Recognition, as on multiple-choice test, only involves determining which item from a list seems most correct (Haist, Shimamura, & Squire, 1992). Although they involve different processes, recall and recognition memory measures tend to be correlated. Students who do better on a multiple-choice exam will also, by and large, do better on an essay exam (Bridgeman & Morgan, 1996).

A third way of measuring memory is known as relearning (Nelson, 1985). Measures of relearning (or savings) assess how much more quickly information is processed or learned when it is studied again after it has already been learned but then forgotten . If you have taken some French courses in the past, for instance, you might have forgotten most of the vocabulary you learned. But if you were to work on your French again, you’d learn the vocabulary much faster the second time around. Relearning can be a more sensitive measure of memory than either recall or recognition because it allows assessing memory in terms of “how much” or “how fast” rather than simply “correct” versus “incorrect” responses. Relearning also allows us to measure memory for procedures like driving a car or playing a piano piece, as well as memory for facts and figures.

Implicit Memory

While explicit memory consists of the things that we can consciously report that we know, implicit memory refers to knowledge that we cannot consciously access. However, implicit memory is nevertheless exceedingly important to us because it has a direct effect on our behaviour. Implicit memory refers to the influence of experience on behaviour, even if the individual is not aware of those influences . As you can see in Figure 9.2, “Types of Memory,” there are three general types of implicit memory: procedural memory, classical conditioning effects, and priming.

Procedural memory refers to our often unexplainable knowledge of how to do things . When we walk from one place to another, speak to another person in English, dial a cell phone, or play a video game, we are using procedural memory. Procedural memory allows us to perform complex tasks, even though we may not be able to explain to others how we do them. There is no way to tell someone how to ride a bicycle; a person has to learn by doing it. The idea of implicit memory helps explain how infants are able to learn. The ability to crawl, walk, and talk are procedures, and these skills are easily and efficiently developed while we are children despite the fact that as adults we have no conscious memory of having learned them.

A second type of implicit memory is classical conditioning effects , in which we learn, often without effort or awareness, to associate neutral stimuli (such as a sound or a light) with another stimulus (such as food), which creates a naturally occurring response, such as enjoyment or salivation . The memory for the association is demonstrated when the conditioned stimulus (the sound) begins to create the same response as the unconditioned stimulus (the food) did before the learning.

The final type of implicit memory is known as priming , or changes in behaviour as a result of experiences that have happened frequently or recently . Priming refers both to the activation of knowledge (e.g., we can prime the concept of kindness by presenting people with words related to kindness) and to the influence of that activation on behaviour (people who are primed with the concept of kindness may act more kindly).

One measure of the influence of priming on implicit memory is the word fragment test , in which a person is asked to fill in missing letters to make words. You can try this yourself: First, try to complete the following word fragments, but work on each one for only three or four seconds. Do any words pop into mind quickly?

_ i b _ a _ y

_ h _ s _ _ i _ n

_ h _ i s _

Now read the following sentence carefully:

“He got his materials from the shelves, checked them out, and then left the building.”

Then try again to make words out of the word fragments.

I think you might find that it is easier to complete fragments 1 and 3 as “library” and “book,” respectively, after you read the sentence than it was before you read it. However, reading the sentence didn’t really help you to complete fragments 2 and 4 as “physician” and “chaise.” This difference in implicit memory probably occurred because as you read the sentence, the concept of “library” (and perhaps “book”) was primed, even though they were never mentioned explicitly. Once a concept is primed it influences our behaviours, for instance, on word fragment tests.

Our everyday behaviours are influenced by priming in a wide variety of situations. Seeing an advertisement for cigarettes may make us start smoking, seeing the flag of our home country may arouse our patriotism, and seeing a student from a rival school may arouse our competitive spirit. And these influences on our behaviours may occur without our being aware of them.

Research Focus: Priming Outside Awareness Influences Behaviour

One of the most important characteristics of implicit memories is that they are frequently formed and used automatically , without much effort or awareness on our part. In one demonstration of the automaticity and influence of priming effects, John Bargh and his colleagues (Bargh, Chen, & Burrows, 1996) conducted a study in which they showed undergraduate students lists of five scrambled words, each of which they were to make into a sentence. Furthermore, for half of the research participants, the words were related to stereotypes of the elderly. These participants saw words such as the following:

in Victoria retired live people

bingo man the forgetful plays

The other half of the research participants also made sentences, but from words that had nothing to do with elderly stereotypes. The purpose of this task was to prime stereotypes of elderly people in memory for some of the participants but not for others.

The experimenters then assessed whether the priming of elderly stereotypes would have any effect on the students’ behaviour — and indeed it did. When the research participant had gathered all of his or her belongings, thinking that the experiment was over, the experimenter thanked him or her for participating and gave directions to the closest elevator. Then, without the participants knowing it, the experimenters recorded the amount of time that the participant spent walking from the doorway of the experimental room toward the elevator. As you can see in Figure 9.3, “Research Results.” participants who had made sentences using words related to elderly stereotypes took on the behaviours of the elderly — they walked significantly more slowly as they left the experimental room.

To determine if these priming effects occurred out of the awareness of the participants, Bargh and his colleagues asked still another group of students to complete the priming task and then to indicate whether they thought the words they had used to make the sentences had any relationship to each other, or could possibly have influenced their behaviour in any way. These students had no awareness of the possibility that the words might have been related to the elderly or could have influenced their behaviour.

Stages of Memory: Sensory, Short-Term, and Long-Term Memory

Another way of understanding memory is to think about it in terms of stages that describe the length of time that information remains available to us. According to this approach (see Figure 9.4, “Memory Duration”), information begins in sensory memory , moves to short-term memory , and eventually moves to long-term memory . But not all information makes it through all three stages; most of it is forgotten. Whether the information moves from shorter-duration memory into longer-duration memory or whether it is lost from memory entirely depends on how the information is attended to and processed.

Sensory Memory

Sensory memory  refers to the brief storage of sensory information . Sensory memory is a memory buffer that lasts only very briefly and then, unless it is attended to and passed on for more processing, is forgotten. The purpose of sensory memory is to give the brain some time to process the incoming sensations, and to allow us to see the world as an unbroken stream of events rather than as individual pieces.

Visual sensory memory is known as iconic memory . Iconic memory was first studied by the psychologist George Sperling (1960). In his research, Sperling showed participants a display of letters in rows, similar to that shown in Figure 9.5, “Measuring Iconic Memory.” However, the display lasted only about 50 milliseconds (1/20 of a second). Then, Sperling gave his participants a recall test in which they were asked to name all the letters that they could remember. On average, the participants could remember only about one-quarter of the letters that they had seen.

Sperling reasoned that the participants had seen all the letters but could remember them only very briefly, making it impossible for them to report them all. To test this idea, in his next experiment, he first showed the same letters, but then after the display had been removed, he signaled to the participants to report the letters from either the first, second, or third row. In this condition, the participants now reported almost all the letters in that row. This finding confirmed Sperling’s hunch: participants had access to all of the letters in their iconic memories, and if the task was short enough, they were able to report on the part of the display he asked them to. The “short enough” is the length of iconic memory, which turns out to be about 250 milliseconds (¼ of a second).

Auditory sensory memory is known as echoic memory . In contrast to iconic memories, which decay very rapidly, echoic memories can last as long as four seconds (Cowan, Lichty, & Grove, 1990). This is convenient as it allows you — among other things — to remember the words that you said at the beginning of a long sentence when you get to the end of it, and to take notes on your psychology professor’s most recent statement even after he or she has finished saying it.

In some people iconic memory seems to last longer, a phenomenon known as eidetic imagery (or photographic memory ) in which people can report details of an image over long periods of time . These people, who often suffer from psychological disorders such as autism, claim that they can “see” an image long after it has been presented, and can often report accurately on that image. There is also some evidence for eidetic memories in hearing; some people report that their echoic memories persist for unusually long periods of time. The composer Wolfgang Amadeus Mozart may have possessed eidetic memory for music, because even when he was very young and had not yet had a great deal of musical training, he could listen to long compositions and then play them back almost perfectly (Solomon, 1995).

Short-Term Memory

Most of the information that gets into sensory memory is forgotten, but information that we turn our attention to, with the goal of remembering it, may pass into short-term memory . Short-term memory (STM)  is the place where small amounts of information can be temporarily kept for more than a few seconds but usually for less than one minute (Baddeley, Vallar, & Shallice, 1990). Information in short-term memory is not stored permanently but rather becomes available for us to process, and the processes that we use to make sense of, modify, interpret, and store information in STM are known as working memory .

Although it is called memory, working memory is not a store of memory like STM but rather a set of memory procedures or operations. Imagine, for instance, that you are asked to participate in a task such as this one, which is a measure of working memory (Unsworth & Engle, 2007). Each of the following questions appears individually on a computer screen and then disappears after you answer the question:

To successfully accomplish the task, you have to answer each of the math problems correctly and at the same time remember the letter that follows the task. Then, after the six questions, you must list the letters that appeared in each of the trials in the correct order (in this case S, R, P, T, U, Q).

To accomplish this difficult task you need to use a variety of skills. You clearly need to use STM, as you must keep the letters in storage until you are asked to list them. But you also need a way to make the best use of your available attention and processing. For instance, you might decide to use a strategy of repeat the letters twice, then quickly solve the next problem, and then repeat the letters twice again including the new one. Keeping this strategy (or others like it) going is the role of working memory’s central executive  —  the part of working memory that directs attention and processing . The central executive will make use of whatever strategies seem to be best for the given task. For instance, the central executive will direct the rehearsal process, and at the same time direct the visual cortex to form an image of the list of letters in memory. You can see that although STM is involved, the processes that we use to operate on the material in memory are also critical.

Short-term memory is limited in both the length and the amount of information it can hold. Peterson and Peterson (1959) found that when people were asked to remember a list of three-letter strings and then were immediately asked to perform a distracting task (counting backward by threes), the material was quickly forgotten (see Figure 9.6, “STM Decay”), such that by 18 seconds it was virtually gone.

One way to prevent the decay of information from short-term memory is to use working memory to rehearse it. Maintenance rehearsal  is the process of repeating information mentally or out loud with the goal of keeping it in memory . We engage in maintenance rehearsal to keep something that we want to remember (e.g., a person’s name, email address, or phone number) in mind long enough to write it down, use it, or potentially transfer it to long-term memory.

If we continue to rehearse information, it will stay in STM until we stop rehearsing it, but there is also a capacity limit to STM. Try reading each of the following rows of numbers, one row at a time, at a rate of about one number each second. Then when you have finished each row, close your eyes and write down as many of the numbers as you can remember.

If you are like the average person, you will have found that on this test of working memory, known as a digit span test , you did pretty well up to about the fourth line, and then you started having trouble. I bet you missed some of the numbers in the last three rows, and did pretty poorly on the last one.

The digit span of most adults is between five and nine digits, with an average of about seven. The cognitive psychologist George Miller (1956) referred to “seven plus or minus two” pieces of information as the magic number in short-term memory. But if we can only hold a maximum of about nine digits in short-term memory, then how can we remember larger amounts of information than this? For instance, how can we ever remember a 10-digit phone number long enough to dial it?

One way we are able to expand our ability to remember things in STM is by using a memory technique called chunking . Chunking  is the process of organizing information into smaller groupings (chunks), thereby increasing the number of items that can be held in STM . For instance, try to remember this string of 12 letters:

XOFCBANNCVTM

You probably won’t do that well because the number of letters is more than the magic number of seven.

Now try again with this one:

CTVCBCTSNHBO

Would it help you if I pointed out that the material in this string could be chunked into four sets of three letters each? I think it would, because then rather than remembering 12 letters, you would only have to remember the names of four television stations. In this case, chunking changes the number of items you have to remember from 12 to only four.

Experts rely on chunking to help them process complex information. Herbert Simon and William Chase (1973) showed chess masters and chess novices various positions of pieces on a chessboard for a few seconds each. The experts did a lot better than the novices in remembering the positions because they were able to see the “big picture.” They didn’t have to remember the position of each of the pieces individually, but chunked the pieces into several larger layouts. But when the researchers showed both groups random chess positions — positions that would be very unlikely to occur in real games — both groups did equally poorly, because in this situation the experts lost their ability to organize the layouts (see Figure 9.7, “Possible and Impossible Chess Positions”). The same occurs for basketball. Basketball players recall actual basketball positions much better than do nonplayers, but only when the positions make sense in terms of what is happening on the court, or what is likely to happen in the near future, and thus can be chunked into bigger units (Didierjean & Marmèche, 2005).

If information makes it past short term-memory it may enter long-term memory (LTM) , memory storage that can hold information for days, months, and years . The capacity of long-term memory is large, and there is no known limit to what we can remember (Wang, Liu, & Wang, 2003). Although we may forget at least some information after we learn it, other things will stay with us forever. In the next section we will discuss the principles of long-term memory.

Key Takeaways

• Memory refers to the ability to store and retrieve information over time.
• For some things our memory is very good, but our active cognitive processing of information ensures that memory is never an exact replica of what we have experienced.
• Explicit memory refers to experiences that can be intentionally and consciously remembered, and it is measured using recall, recognition, and relearning. Explicit memory includes episodic and semantic memories.
• Measures of relearning (also known as “savings”) assess how much more quickly information is learned when it is studied again after it has already been learned but then forgotten.
• Implicit memory refers to the influence of experience on behaviour, even if the individual is not aware of those influences. The three types of implicit memory are procedural memory, classical conditioning, and priming.
• Information processing begins in sensory memory, moves to short-term memory, and eventually moves to long-term memory.
• Maintenance rehearsal and chunking are used to keep information in short-term memory.
• The capacity of long-term memory is large, and there is no known limit to what we can remember.

Exercises and Critical Thinking

• List some situations in which sensory memory is useful for you. What do you think your experience of the stimuli would be like if you had no sensory memory?
• Describe a situation in which you need to use working memory to perform a task or solve a problem. How do your working memory skills help you?

Atkinson, R. C., & Shiffrin, R. M. (1968). Human memory: A proposed system and its control processes. In K. Spence (Ed.),  The psychology of learning and motivation  (Vol. 2). Oxford, England: Academic Press.

Baddeley, A. D., Vallar, G., & Shallice, T. (1990). The development of the concept of working memory: Implications and contributions of neuropsychology. In G. Vallar & T. Shallice (Eds.),  Neuropsychological impairments of short-term memory  (pp. 54–73). New York, NY: Cambridge University Press.

Bargh, J. A., Chen, M., & Burrows, L. (1996). Automaticity of social behavior: Direct effects of trait construct and stereotype activation on action.  Journal of Personality & Social Psychology, 71 , 230–244.

Bridgeman, B., & Morgan, R. (1996). Success in college for students with discrepancies between performance on multiple-choice and essay tests.  Journal of Educational Psychology, 88 (2), 333–340.

Cowan, N., Lichty, W., & Grove, T. R. (1990). Properties of memory for unattended spoken syllables.  Journal of Experimental Psychology: Learning, Memory, and Cognition, 16 (2), 258–268.

Didierjean, A., & Marmèche, E. (2005). Anticipatory representation of visual basketball scenes by novice and expert players.  Visual Cognition, 12 (2), 265–283.

Haist, F., Shimamura, A. P., & Squire, L. R. (1992). On the relationship between recall and recognition memory.  Journal of Experimental Psychology: Learning, Memory, and Cognition, 18 (4), 691–702.

Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information.  Psychological Review, 63 (2), 81–97.

Nelson, T. O. (1985). Ebbinghaus’s contribution to the measurement of retention: Savings during relearning.  Journal of Experimental Psychology: Learning, Memory, and Cognition, 11 (3), 472–478.

Peterson, L., & Peterson, M. J. (1959). Short-term retention of individual verbal items.  Journal of Experimental Psychology, 58 (3), 193–198.

Simon, H. A., & Chase, W. G. (1973). Skill in chess.  American Scientist, 61 (4), 394–403.

Solomon, M. (1995).  Mozart: A life . New York, NY: Harper Perennial.

Sperling, G. (1960). The information available in brief visual presentation.  Psychological Monographs, 74 (11), 1–29.

Unsworth, N., & Engle, R. W. (2007). On the division of short-term and working memory: An examination of simple and complex span and their relation to higher order abilities.  Psychological Bulletin, 133 (6), 1038–1066.

Wang, Y., Liu, D., & Wang, Y. (2003). Discovering the capacity of human memory.  Brain & Mind, 4 (2), 189–198.

Image Attributions

Figure 9.4: Adapted from Atkinson & Shiffrin (1968).

Figure 9.5: Adapted from Sperling (1960).

Figure 9.6: Adapted from Peterson & Peterson (1959).

Introduction to Psychology - 1st Canadian Edition Copyright © 2014 by Jennifer Walinga and Charles Stangor is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Memory is our only way of travelling to the past. on it, we store our best moments, interesting knowledge (and also that silly fun fact you once read in a tweet). memory is very important because it helps us take better decisions and it connects us with people who aren’t by our side anymore. this mysterious ability from our brain is very complicated and we still haven’t discovered everything there is to know about it. where is it stored how can we repair it once it's broken with this collection of slides you will be able to speak about everything that has to do with memory are you looking for medicine templates about the brain and its functions maybe you want to hold a memorial for a loved one or remember the importance of a day there’s a template waiting for you here.

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Lost Sock Memorial Day

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My First Communion Memory Book

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Memory Game

Browsing Slidesgo looking for a funny presentation? How about this: a new template structured as a memory game where you can challenge a friend or a relative to see who scores more points! Colorful slides, pastel tones and many different designs. It’s the perfect choice for a young audience!

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Memory-based modes of presentation

• Original Research
• Open access
• Published: 08 April 2024
• Volume 203 , article number  116 , ( 2024 )

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• François Recanati   ORCID: orcid.org/0000-0002-8642-2954 1  

To deal with memory-based modes of presentation I propose a couple of revisions to the standard criterion of difference for modes of presentation attributed to Frege. First, we need to broaden the scope of the criterion so that not merely the thoughts of a given subject at a given time may or may not involve the same way of thinking of some object, but also the thoughts of a subject at different times. Second, we need to ‘relativize’ the criterion of difference to particular subjects in particular situations. Thanks to these revisions, we can make sense of Evans’ notion of a dynamic mode of presentation that persists through time despite lower-level changes. A dynamic mode of presentation is a complex mode of presentation involving several epistemically rewarding relations to the reference successively (in contrast to composite modes of presentation, which involve several epistemically rewarding relations simultaneously). I show how this idea can be cashed out in the mental file framework, and how, in that framework, we can provide a straightforward answer to the question: when is a mode of presentation based on a memory M the same as the mode of presentation based on the perception P from which the memory derives? The answer appeals to the distinction between anchored and unanchored memories.

Avoid common mistakes on your manuscript.

1 Modes of presentation: the criterion of difference

Frege’s distinction beween sense and reference rests on the following observation. Two linguistic expressions may refer to the same thing, as a matter of fact, yet a subject who fully understands these expressions may fail to realize that they do. What this shows, according to Frege, is that what a subject grasps when she understands an expression is the sense of that expression, rather than directly its reference. The sense of an expression corresponds to the way in which the reference is presented when that expression is used. Two expressions (e.g. ‘Cicero’ and ‘Tully’, or ‘the morning star’ and ‘the evening star’) may refer to the same thing yet present that thing differently, under different aspects. In such a case, a linguistically competent subject may fail to realize that the expressions refer to the same thing. What is transparent to the subject (what she grasps) is the sense of the expression, but the reference remains opaque to the extent that it depends upon worldly facts beyond the subject’s knowledge.

In the analytic tradition the following ‘criterion of difference’ for modes of presentation (senses) is standardly ascribed to Frege:

Two coreferential expressions ‘ a ’ and ‘ b ’ are associated with distinct senses, i.e. present their common reference in two distinct ways, if a rational subject could assent to ‘ a is F’ and simultaneously withhold assent from, or reject, ‘ b is F’.

A situation in which a rational subject accepts contradictory predications regarding what is in fact one and the same object is known as a ‘Frege case’ (Fodor, 1994 ). The criterion of difference uses the possibility of such cases to diagnose distinctness in sense among coreferential expressions.

The formulation of the Fregean criterion I have just cited is roughly that given by Gareth Evans ( 1982 ). Evans points out that the criterion of difference for modes of presentation derives from Frege’s criterion of difference for thoughts:

The thought associated with one sentence S as its sense must be different from the thought associated with another sentence S’ as its sense, if it is possible for someone to understand both sentences at a given time while coherently taking different attitudes towards them, i.e. accepting (rejecting) one while rejecting (accepting), or being agnostic about, the other. (Evans, 1982 : p. 19)

This criterion itself ‘rests upon the principle that it is not possible coherently to take different attitudes towards the same thought’ (Evans, 1981 , 1985 : p. 308).

In a footnote, Evans makes an interesting observation. He points out that Frege’s criterion of difference for thoughts would give incorrect results if we substituted ‘anyone’ for ‘someone’, that is, if we said that the thoughts expressed by two sentences are distinct if it is possible for anyone to understand both sentences at a given time while coherently taking different attitudes towards them. The substitution is illegitimate, Evans points out, for the following reason:

The thought expressed by ‘Hesperus if F’ is distinct from the thought expressed by ‘Phosphorus is F’, but it is not true that anyone who understands the two sentences can take different attitudes to them. For example, it is not true of someone who knows that Hesperus if Phosphorus. (Evans, 1982 : p. 19, fn 19) Footnote 1

In other words, not all rational subjects are in a situation such that it would be coherent for them to ascribe contradictory properties to one and the same object presented under two distinct modes of presentation. Such an ascription would be incoherent for any subject who is aware of the identity. But to establish, via the criterion of difference, that two coreferential expressions are associated with distinct modes of presentation, it suffices that some rational subject (some rational subject or other) could coherently make these contradictory predications. Footnote 2

The sense of a linguistic expression is the way it presents its reference, but the distinction between the thing referred to and the way it is presented is not restricted to language. It applies to silent thought as well. The object we’re thinking about is one thing and the way we are thinking of it is another. There are different ways of thinking of a given object, and they deserve the label ‘modes of presentation’, whether or not they are linguistically expressed. We should therefore reformulate the criterion of difference for modes of presentation so as to make it independent of language. The following formulation, due to Stephen Schiffer, gives us what we need:

If a minimally rational person x believes a thing y to be F (…) and also believes y not to be F, then there are distinct modes of presentation m and m’ such that x believes y to be F under m and disbelieves y to be F under m’ . (Schiffer, 1978 : p. 180)

2 Reference through memory

Sometimes we remember an object we previously encountered and have a thought about it. In such a case the thought is about the object we remember, and a particular ‘way of thinking’ of the object seems to be involved: we think of the object through our memory of it. The relevant way of thinking seems to be different from another way of thinking involving perception rather than memory. Thus, in (1) and (2) below, the speaker expresses thoughts that involve a memory-based mode of presentation and a perception-based mode of presentation respectively:

I wonder what sort of bird that was [based on the memory of an event that took place the previous year]

I wonder what sort of bird that is [based on current perception]

The demonstrative ‘that’ is the same in (1) and (2), but it is associated with distinct modes of presentation. In (1) the demonstrative is what Evans calls a ‘past-tense demonstrative’, one that is associated with a memory-based mode of presentation (Evans, 1982 : pp. 135, 306). Footnote 3

Contrary to what the contrast between (1) and (2) may suggest, grammatical tense is not essential to distinguish one type of case from the other. No grammatical feature is essential, arguably: one and the same sentence containing a demonstrative can be used to express a thought involving either a perception-based or a memory-based mode of presentation. Thus consider the following examples:

That banana was in the fridge

That banana is in the fridge

Sentence (3) is in the past tense, but the demonstrative phrase ‘that banana’ need not be a past-tense demonstrative associated with the memory of a certain banana: it may also be an ordinary demonstrative associated with the current perception of a certain banana. (Imagine the subject is holding a banana and, based on its felt temperature, judges: ‘that banana was in the fridge—it’s pretty cold’.) Conversely, sentence (4) is in the present tense, but the demonstrative phrase ‘that banana’ need not be an ordinary demonstrative associated with the perception of a certain banana; it may also be used to refer to a particular banana the speaker remembers, and of which he conjectures that it is now in the fridge.

The distinction between perception-based and memory-based modes of presentation is fairly intuitive. It’s one thing to think of an object as the object we are currently perceiving, and another to think of it through the memory trace left by an earlier perception. But can we establish that the two modes of presentation are distinct by appealing to the Fregean criterion of difference? That is the question that matters for us now.

To establish, by means of the Fregean criterion of difference, that that banana memory and that banana perception are distinct modes of presentation, we need to consider a situation in which a rational subject takes conflicting attitudes towards thoughts that differ only by the substitution of one mode of presentation for the other. If such a situation is possible or imaginable, then, by the Fregean criterion, the modes of presentation are distinct. That is indeed what we find: we can easily imagine a situation in which the subject remembers a certain banana and suspends judgment as to whether that banana has ever been in the fridge, while, at the same time, perceiving (what is in fact) the same (unrecognized) banana and judging, on the basis of its felt temperature, that that banana was in the fridge shortly before.

In this case there is a memory (call it M) and two perceptions: the perception P1 that is the source of the memory and the perception P2 which is simultaneous with the memory. By the criterion of difference we can establish that the mode of presentation based on M and the mode of presentation based on P2 are distinct modes of presentation; and we can do so because the two modes of presentation (that based on M and that based on P2) are simultaneously deployed, in such a way that the criterion of difference can apply. As Dickie and Rattan point out, ‘[The criterion of difference] is synchronic and intrapersonal – it deals in rational engagement between the attitudes that a single subject has at a time’ (Dickie & Rattan, 2010 : p. 146). It follows that it can only be invoked when the conflicting attitudes at issue are simultaneous. In the case of M and P2, the simultaneity condition is satisfied, but it is not in the case of M and P1. So we cannot establish that the mode of presentation based on M is distinct from the mode of presentation under which the subject thought of the banana when she initially encountered it , during episode P1; for these modes of presentation (that based on P1 and that based on M) are not simultaneously deployed. P1 takes place first, and M follows later.

A similar problem famously arises with ‘today’ and ‘yesterday’. It seems that to think of a certain day as ‘today’ and to think of it the next day as ‘yesterday’ are two different ways of thinking of one and the same day. But the fact that these are distinct modes of presentation of the day in question cannot be established by appealing to the Fregean criterion (Evans, 1981 , 1985 : pp. 307–308). The criterion of difference cannot do its work unless someone is able simultaneously to entertain the thoughts expressed by, for example, ‘Today is fine’ and ‘Yesterday was fine’, with ‘today’ and ‘yesterday’ referring to the same day. But there is no way in which a subject can think of a single day both as ‘today’ and as ‘yesterday’, at the same time. So there is no way in which we can check whether a rational subject thinking of a single day d both as today and as yesterday at the same time could or could not hold conflicting attitudes towards the thought expressed by means of ‘today’ and that expressed by means of ‘yesterday’.

Not only can we not establish the distinctness of the modes of presentation in these cases by appealing to the criterion of difference. There are also reasons to believe that the relevant modes of presentation (that associated with ‘today’ and that associated the next day with ‘yesterday’, or that based on P1 and that subsequently based on M) are actually the same mode of presentation persisting through time . Thus Frege wrote:

If someone wants to say today what he expressed yesterday using the word 'today', he will replace this word with 'yesterday'. Although the thought is the same, the verbal expression must be different in order that the change of sense which would otherwise be effected by the differing times of utterance may be cancelled out. (‘Thoughts’, in Frege, 1984 : p. 358)

For Frege, ‘the thought is the same’, when you think of a certain day as ‘today’ and when, the following day, you think of it as ‘yesterday’. Evans made a similar claim. He argued that temporal thoughts such as ‘Today is fine’ (tokened on a certain day) and ‘Yesterday was fine’ (tokened the next day) are ‘cross-sections of a persisting belief state which exploits our ability to keep track of a moment as it recedes in time’ (Evans, 1981 , 1985 : p. 310). It follows that.

A subject on d 2 is thinking of d 1 in the same way as on d 1 , despite lower level differences, because the thought episodes on the two days depend upon the same exercise of a capacity to keep track of time. (Evans, 1981 , 1985 : p. 311)

Ninan ( 2015 ) also argues that, in such cases, the modes of presentation are the same despite lower-level differences. This is a controversial position, Footnote 4 of course, but we cannot use the criterion of difference to settle the issue, because the simultaneity condition is not satisfied.

3 Making the criterion of difference diachronic

To overcome the limitation I have just pointed out (i.e. the fact that the criterion of difference only applies when the simultaneity condition is satisfied), two distinct strategies offer themselves.

The first strategy consists in imagining extraordinary circumstances in which the relevant modes of presentation can be simultaneously deployed. Think of the movie Groundhog Day : the main character, Phil Connors, is trapped in a time loop forcing him to relive the same day (February 2, Groundhog Day) repeatedly. The first time this happens, Phil comes to realize that the day he is currently living through is not a fresh day but the same day as the previous day. In these admittedly strange circumstances, Phil can think of the day in question both as ‘today’ and as ‘yesterday’, at the same time. He can also doubt the identity and ascribe to the current day properties (like the fact that he himself remembers living through February 2) that the previous day did not possess. By the Fregean criterion of difference, that imaginable situation is sufficient to establish that the yesterday -mode of presentation and the today -mode of presentation are distinct modes of presentation.

Another, more easily generalizable strategy consists in avoiding such far-fetched (and possibly incoherent) examples and explicitly lifting the simultaneity condition built into the criterion of difference. Thus, in the forthcoming paper I have just mentioned (see footnote 4), I formulated two variants of the criterion, a synchronic variant that applies to simultaneous cases and a diachronic variant that applies to non-simultaneous cases:

Synchronic variant m and m’ are distinct modes of presentation if the following conditions are satisfied: (a) it is possible for a subject simultaneously to believe of a given object, thought of under m , that it is F, and to hold a conflicting attitude (e.g. disbelief) toward the thought that results from substituting m’ for m ; (b) that is possible without irrationality on the subject’s part. Diachronic variant m and m’ are distinct modes of presentation if the following conditions are satisfied: (a) it is possible for a subject to believe of a given object, thought of under m , that it is F, and at a later time to hold a conflicting attitude (e.g. disbelief) toward the thought that results from substituting m’ for m in the initial thought; (b) that is possible without change of mind on the subject’s part. (Recanati, forthcoming, Sect. 5).

Using the diachronic variant, we can easily establish that the yesterday -mode of presentation and the today -mode of presentation are distinct modes of presentation. It has been observed (by Tyler Burge) that

It is possible to believe what is expressed by ‘Today is Friday’ and (without in any ordinary sense changing one's mind) doubt what is expressed by ‘Yesterday was Friday,’ even though ‘yesterday’ and ‘today’ (in their different contexts) pick out the same day. (Burge, 1979 : p. 402)

By the diachronic variant of the criterion of difference, that epistemic possibility, whose existence can hardly be disputed, shows that ‘today’ and ‘yesterday’ express distinct modes of presentation.

To be sure, as Evans emphasized, that epistemic possibility is ruled out if the subject has ‘kept track of time’. Only a temporally confused subject can, on a certain day, believe what is expressed by ‘Today is Friday’ and the following day, without changing one's mind, doubt what is expressed by ‘Yesterday was Friday.’ But, as Evans himself pointed out in the footnote I quoted before, the epistemic possibility invoked by the criterion of difference must only be a possibility for some rational subject (here, the confused subject); it need not be an epistemic possibility for every rational subject. Just as a subject who knows that Hesperus is Phosphorus cannot, without irrationality, ascribe contradictory properties to Venus thought of as ‘Hesperus’ and to Venus thought of as ‘Phosphorus’, a subject who has kept track of time cannot, without changing his mind, doubt what is expressed by ‘Yesterday was Friday’ if the previous day he accepted ‘Today is Friday’.

4 Campbell’s criterion

The criterion of difference only gives us a sufficient condition for distinctness among modes of presentation. Another criterion has been put forward, however. Campbell’s criterion, as I will call it, provides a sufficient condition for identity among modes of presentation.

There is a well-known distinction between two types of coreference relations between singular terms. Coreference is said to be ‘de facto’ if it is possible for a rational and linguistically competent subject not to realize that the singular terms refer to the same thing. That is what happens when the singular terms are associated with distinct modes of presentation of what turns out to be the same object. By contrast, coreference is ‘de jure’ if it is not possible not to realize that the singular terms refer to the same object (Recanati, 2016 , 2020 , 2021 ). That is the type of coreference relation that is instantiated, for example, between an anaphoric pronoun and its referential antecedent, as in: ‘Roderick i was a philosopher. He i was extremely well-read.’ Anyone who understands the discourse knows that the pronoun and its antecedent corefer (if they refer at all).

When two coreferential singular terms a and b (construed as tokens which may or may not be of the same type) are coreferential de jure in this manner, it would be irrational to accept that a is F and b is G while not accepting that a single object is both F and G (existential conjunction). The subject is therefore entitled to embrace that conclusion, without having to appeal to an additional identity premise such as ‘a  =  b’ . That inference pattern (‘ a is F; b is G; therefore, something is F and G’) is what Campbell calls ‘Trading on coreference’ (TC). For example, in the table below (from Recanati, 2012 : p. 48), the left-hand column is an instance of TC:

In the left-hand column the two occurrences of the name ‘Cicero’ are de jure coreferential, so TC is allowed: the two premises directly support the conclusion. In the right-hand column, the coreference is de facto and an additional premise (‘Cicero = Tully’) is needed to reach the conclusion.

The example I have just given may suggest that, for TC to be licensed, the token singular terms must of the same type. But that is not the case. The first example of coreference de jure I gave, where the relevant singular terms are an anaphoric pronoun and its antecedent, also licenses TC:

Roderick is a philosopher. He is extremely well-read. Some philosopher is extremely well-read.

According to Campbell what makes TC possible is not type identity but the fact that the two singular terms ‘have the same sense’:

We have to separate two types of case. In the first, we trade directly upon co-reference, moving directly to the conclusion. (…) It seems to me that we can do this just when the two tokens have the same sens e. In the second type of case, when the tokens do not have the same sense, it would not be legitimate to move directly to the conclusion. (Campbell, 1987  : pp. 275-76; emphasis mine).

This gives rise to Campbell’s criterion—a criterion for sameness of sense:

Campbell’s criterion If two token singular terms allow ‘trading on coreference’ (TC), they have the same sense.

This criterion seems not to be subject to the limitations which affect the standard (synchronic) version of the criterion of difference. Thus Campbell gives an example in which his criterion applies even though the simultaneity condition is not satisfied:

A man sitted in a wasp-filled garden may see a wasp and think ‘That wasp is F’. Some time later, having lost track of the first wasp in the meantime, he may see a wasp and think, ‘That wasp is G’. Even if it is in fact the same wasp that is in question, our subject surely could not infer directly from those two judgments that ‘there is something that is both F and G’. The transition would have to be mediated by a further premise, to the effect that it was the same wasp on both occasions. (Campbell, 1987 : p. 278)

Now imagine that the subject has kept track of the initial wasp, rather than lost track of it:

If (…) one does succeed in keeping track of a particular wasp over time, (…) and makes the judgments, ‘That wasp is F’ and ‘That wasp is G’, then one must know immediately that it is the same thing that is in question. (Campbell, 1987 : p. 285)

In this case TC is possible:

That wasp is F

That wasp is G

Therefore something is both F and G

By Campbell’s criterion, we can therefore conclude that, when the subject keeps track of the initial wasp, he keeps thinking of it in the same way throughout the perceptual episode. In other words, the two occurrences of the demonstrative phrase ‘that wasp’ in (1) and in (2) carry the same sense, in such a case, even though they occur at different times.

5 When the criteria conflict: relativizing the criterion of difference

The subject who has kept track of the wasp does not doubt that the wasp he is seeing is the wasp he has seen a moment before: the identity is presupposed , so the subject can unreflectively trade on coreference. By Campbell’s criterion, that establishes that the two successive occurrences of the demonstrative phrase ‘that wasp’ carry the same sense even though they occur at different times. But if we appeal to the criterion of difference, understood according to what I called the ‘absolute’ interpretation (footnote 2), we have to say that the modes of presentation are different because another subject, or the same subject in a different context , might doubt the identity of the wasp seen at different times during the episode. So Campbell’s criterion and the criterion of difference thus interpreted give conflicting verdicts, and we can’t simply use them to complement each other. We need to adjudicate between them.

The same conflict arises in synchronic cases. Suppose I hold a banana in my hand while looking at it. I judge:

That banana is cold (based on touch). That banana is yellow (based on vision).

Since it is obvious to me that the banana I feel in my hand is the banana I see, TC is allowed and I can move directly to the conclusion:

Something is yellow and cold.

This suggests that the two occurrences of the demonstrative phrase ‘that banana’ are associated with the same mode of presentation (by Campbell’s criterion). That mode of presentation presumably is a multi-modal mode of presentation involving both vision and touch. By the criterion of difference, however, the modes of presentation are distinct, because a rational subject with different epistemic dispositions might doubt (rather than take for granted) that the seen banana is the same as the touched banana.

The source of the conflict is the following. For the criterion of difference as I have interpreted it so far, what matters are the epistemic dispositions of some rational subject or other (‘absolute’ interpretation). Even if we are talking about a situation in which it is taken for granted that a  =  b (e.g. that Hesperus is Phosphorus, or that the seen banana is the touched banana, or that the initial wasp is the current wasp), the fact that some rational subject or other might doubt the identity is sufficient to establish that the modes of presentation are distinct. For example, the fact that some subject might have lost track of the wasp is sufficient to establish that the modes of presentation associated with the two successive occurrences of the phrase ‘that wasp’ are distinct (even for the subject who has kept track). There are distinct modes of presentation (in an absolute sense, i.e. for every subject) provided some subject can doubt the identity. Campbell’s criterion, however, is primarily concerned with the epistemic dispositions of a particular subject in a particular context (‘relativized’ interpretation). For someone who takes it for granted that Hesperus = Phosphorus, or that the seen banana = the touched banana, or that the wasp at t 1  = the wasp at t 2 , the mode of presentation associated with the two singular terms is the same, notwithstanding the fact that some other subject might doubt the identity.

I conclude that we can’t both accept Campbell’s criterion and the criterion of difference as initially interpreted: if we accept Campbell’s criterion, as I believe we should, we must re-interpret the criterion of difference so as to substitute the perspective of a situated subject for the perspective of some rational subject or other. In other words, we need to relativize the criterion of difference. Such relativization is what I advocated in the forthcoming paper I already alluded to twice:

To say that the subject could , at a single time, both assent to ‘ a is F’ and withhold assent from, or reject, ‘ b is F’, is to say that doing so (assenting to ‘ a is F’ while rejecting ‘ b is F’) would be compatible with the subject’s actual dispositions . Now a subject who presupposes identity (as in the TC examples) has no disposition to doubt whether e.g. the seen glass is the touched glass. To be sure, the subject can come to doubt that it is the same glass, but only at the cost of changing her dispositions. Should such a change occur, the subject would no longer be disposed to trade upon coreference. So doubt is always possible, in an absolute sense (Millikan, 1997 : p. 517), but that shows nothing regarding the subject’s actual attitudes and whether she is thinking of the object under one or two distinct modes of presentation. What is relevant to there being a single or distinct modes of presentation is the possibility of doubt (or of conflicting attitudes) compatible with the subject’s actual dispositions . (Recanati, forthcoming, section 6)

That change of perspective is also what Campbell himself explicitly advocates:

What matters, in applying these tests, is whether the subject actually does make a division in the perceptual information he is receiving. The mere possibility of such a division does not show one is actually in a position to ask whether ‘this glass (perceived now) is identical to that glass (perceived a moment ago)’, for example. (…) The principle being mishandled (…) is surely this: If the subject actually does make a division in his perceptual information, so that he can raise the question whether it is the same thing that is in question, then we have two different modes of presentation. (Campbell, 1987 : pp. 284-85)

If, as recommended by both Campbell and myself, we focus on the perspective of a particular subject at a particular time, then the question, whether the modes of presentation are distinct, is raised with respect to that particular subject. The answer may be yes for one subject, but no for another subject. If the subject we are concerned with (in Campbell’s example) has lost track of the initial wasp, then, even if the subject’s thought at t 2 concerns the same wasp as her thought at t 1 , TC is not allowed: an identity premise is necessary to infer the existential conjunction. In such a case, Campbell says, the modes of presentation are distinct (and the coreference is only de facto). If the subject has kept track of the initial wasp, however, the same mode of presentation recurs and TC is allowed.

6 Composite modes of presentation

Consider the banana example once again. The fact that some rational subject might doubt that the seen banana is the same as the touched banana establishes that, for that subject, the visual mode of presentation that banana vision is distinct from the haptic mode of presentation that banana touch . On the other hand, a subject who unreflectively takes it for granted that the seen banana is the touched banana can trade on coreference and reason as follows:

[TC-banana] That banana is cold (based on touch). That banana is yellow (based on vision). Thus, something is yellow and cold.

This establishes, by Campbell’s criterion, that the two occurrences of the phrase ‘that banana’ are associated with the same mode of presentation for that subject. Which mode of presentation is that? It is arguably neither the visual mode of presentation nor the haptic mode of presentation but a multimodal (visuo-tactile) mode of presentation, associated with both premises in the above piece of reasoning. That third mode of presentation can be seen as a composite mode of presentation resulting from the fusion of the first two but distinct from each of them. On this analysis it is true that the visual mode of presentation and the haptic mode of presentation are distinct for the subject who does not presuppose the identity, but it is also true that there is a single, multimodal mode of presentation that is instantiated twice in [TC-banana], in conformity to Campbell’s criterion.

The same type of analysis involving composite modes of presentation applies, though a little less straightforwardly, to the allegedly diachronic instance of TC which Campbell discusses:

[TC-wasp] (1) That wasp is F (judgment made at t 1 ) (2) That wasp is G (judgment made at t 2 , while keeping track of the initial wasp) (3) Thus, something is both F and G

Let us call P1 the perception occurring at t 1 and supporting the judgment in (1), and P2 the perception occurring at t 2 and supporting the judgment in (2). A rational subject could doubt the identity of the wasp seen at t 1 and of the wasp seen at t 2 . For such a subject, the demonstrative phrases respectively occurring in (1) and (2) are associated with distinct perceptual modes of presentation respectively based on P1 and P2. Such a subject would not be disposed to trade upon coreference. But consider a subject who is disposed to trade upon coreference, as in [TC-wasp]. Campbell’s criterion dictates that, for that subject, the modes of presentation associated with the demonstrative phrases respectively occurring in (1) and (2) must be the same. What is the mode of presentation in question?

It is tempting to say that the relevant mode of presentation is a dynamic mode of presentation of the sort postulated by Evans when he claims that the subject who thinks of the current day as ‘today’ thinks of it under the same mode of presentation the following day when he thinks of it as ‘yesterday’. If the subject has kept track of the initial wasp, arguably, the same mode of presentation persists from t 1 to t 2 , and that is why TC is allowed. That is the view Evans and Campbell actually hold: the subject who at t 1 has a thought about a wasp she perceives thinks of the wasp under the same dynamic mode of presentation a moment later (at t 2 ) when she perceives it again provided she hasn’t lost track of it in the meantime.

The notion of a dynamic mode of presentation is important, and I will have more to say about it in the next section; but I don’t think we need it to account for TC as it occurs in [TC-Wasp]. The notion we need, I think, is merely that of a composite mode of presentation. The mode of presentation which the subject who trades upon coreference associates with both occurrences of the demonstrative phrase ‘that wasp’ in [TC-wasp] is such a composite mode of presentation, based on both the perception P2 of the wasp taking place at t 2 , and on the memory M of the wasp seen at t 1 . That memory is the trace left by P1 at t 2 . The subject takes it for granted—presupposes—that the wasp currently seen (at t 2 ) is the wasp seen a moment before (at t 1 ) and remembered. The way the subject thinks of that wasp therefore blends elements derived from the first encounter (at t 1 ) and retained in memory together with elements derived from the current perception (at t 2 ). The key point is that in [TC-wasp] both occurrences of the demonstrative phrase ‘that wasp’ are associated with that composite mode of presentation. That is what makes TC possible.

This analysis raises a prima facie objection. By Campbell’s criterion, the demonstrative phrases respectively occurring in premises (1) and (2) of [TC-wasp] must be associated with the same mode of presentation. I have just said that the mode of presentation in question is a composite mode of presentation based on P2 and M, where M is the memory left by P1 at t 2 . But premise (1) is supposed to be a judgment made at t 1 on the basis of the perception P1 occurring then. So the mode of presentation associated with the phrase ‘that wasp’ in the judgment occurring at t 1 cannot be a composite mode of presentation involving P2 and M, since both P2 and M only come into the picture at t 2 .

To dispose of that objection, we have to realize that [TC-wasp] is a piece of reasoning which, like all pieces of reasoning, must be construed as taking place at a particular time (Recanati, 2016 : p. 77). The time in question is the time when, on the basis of the premises, the subject derives the conclusion. In [TC-wasp], the subject can only derive the conclusion at t 2 since, before t 2 , the second premise was missing. So the reasoning takes place at t 2 , and involves two premises. The first premise tokened at t 2 is the judgment initially made at t 1 on the basis of P1 and preserved through memory . The second premise tokened at t 2 is the judgment made at t 2 on the basis of P2. The perceptual judgment made at t 1 and the reasoning subsequently taking place at t 2 can be represented as follows:

That wasp is F (judgment made at t 1 on the basis of P1)

That wasp is/was F (updated version, at t 2 , of the judgment initially made at t 1 )

That wasp is G (judgment made at t 2 on the basis of P2)

Thus something that is/was F is G

Since at t 2 the subject presupposes that the wasp perceived is the wasp remembered, the way the wasp is thought of at t 2 is simultaneously based on the current perception P2 and on the memory M left by P1. That composite mode of presentation is deployed in both premises tokened at t 2 . So there is a difference between the subject’s thought at t 1 , which involves a mode of presentation of the wasp based on P1, and the thought that serves as first premise in the reasoning taking place at t 2 . The first premise of the reasoning is what the subject has retained, at t 2 , of the initial judgment made at t 1 . As I put in Mental Files in Flux , where I discuss these matters at length,

What the subject has retained is not the initial thought itself, but a variant that results from updating the initial thought (the thought held at t 1 ). (Recanati, 2016 : p 77).

The difference between the initial thought (at t 1 ) and the updated thought (at t 2 ) is a difference in the way the wasp is thought about: at t 1 it is thought of under a perceptual mode of presentation based on P1; at t 2 , however, it is thought of under a composite mode of presentation based on M (the memory of P1) and P2 simultaneously.

7 Dynamic modes of presentation

As I have just shown, we do not need the notion of a dynamic mode of presentation persisting through time to deal with [TC-wasp], given the ultimately synchronic character of the inference at stake (which inference takes place at t 2 ). Still, the notion of a dynamic mode of presentation seems to be what we need to account for the relation between a perceptual mode of presentation instantiated at a given time t 1 and the corresponding memory-based (or memory + perception-based) mode of presentation occurring at a later time t 2 .

There are two types of case to consider: the cases in which, in the interval from t 1 to t 2 , the subject ‘keeps track’, and the cases in which the subject doesn’t. The former are the cases in which the modes of presentation instantiated at t 1 and at t 2 appear to constitute a single dynamic mode of presentation persisting through time.

As we have seen, the diachronic version of the criterion of difference establishes that ‘today’ and ‘yesterday’ are associated with distinct modes of presentation for a subject who has lost track of time. Such a subject can, as Burge puts it, ‘believe what is expressed by Today is Friday and (without in any ordinary sense changing one's mind) doubt what is expressed by Yesterday was Friday , even though ‘yesterday’ and ‘today’ (in their different contexts) pick out the same day’ (Burge, 1979 : p. 402). But no such verdict can be reached for a subject who has kept track of time: such a subject cannot , without changing their mind, doubt what is expressed by ‘Yesterday was Friday’ if the previous day they accepted ‘Today is Friday’. This suggests that there is a single, dynamic mode of presentation of Friday that persists from Friday to Saturday when the subject keeps track of time. That is indeed Evans’ conclusion. Likewise, for Campbell, a subject who keeps track of the wasp from t 1 to t 2 arguably thinks of the wasp under the same dynamic mode of presentation throughout. If Evans and Campbell are right, there are dynamic modes of presentation that persist through time despite what Evans describes as ‘local’ or ‘lower-level’ differences between the way the subject thinks of the object at t 1 and the way she thinks of it at t 2 . On this picture, the difference between the various ‘epistemically rewarding relations’ Footnote 5 to the entity thought about count as lower-level differences which do not affect the (numerical) identity of the dynamic mode of presentation.

Assuming they exist, what are dynamic modes of presentation? Are they a variety of composite modes of presentation? I don’t think they are, but they are interestingly similar to composite modes of presentation. Both composite and dynamic modes of presentation are ‘complex’ modes of presentation, based on several epistemically rewarding relations. A composite mode of presentation is based on several epistemically rewarding relations to the reference simultaneously . The subject presupposes that the various relations in question are relations to one and the same entity. A dynamic mode of presentation is based on several epistemically rewarding relations to the reference successively . As time unfolds, the subject presupposes that he keeps tracking the same entity, despite changes in the contextual relations to that entity. Thus, the subject who has kept track of the wasp and thinks of it at t 2 thinks of it under a composite mode of presentation that embodies the presupposition that the wasp seen at t 2 is the wasp seen at t 1 and remembered. That composite mode of presentation, based on both the memory M of the wasp seen at t 1 and the perception P2 of the wasp seen at t 2 , is clearly distinct from the mode of presentation exclusively based on P1 through which the subject initially thought of the wasp at t 1 ; yet, owing to the presupposition, the perceptual mode of presentation instantiated at t 1 retrospectively counts as the initial stage of a dynamic mode of presentation that persists at t 2 when the subject thinks of the wasp under the composite mode of presentation.

8 Anchored and unanchored memories

To understand the contrast between the cases in which the subject ‘keeps track’ and operates with a single, dynamic mode of presentation, and the cases in which the subject ‘loses track’ and operates with distinct modes of presentation, we can usefully appeal to the mental file framework (Recanati, 2012 , 2016 ).

Think of the wasp example. At t 1 the subject perceptually encounters a wasp (P1), and thinks of it under a mode of presentation based on P1. In the mental file framework the mode of presentation is viewed as a mental file which the subject opens at t 1 , and in which she stores the information gained through P1. At this point there are two options: the subject may either keep track of the wasp, or lose track of it. If the subject keeps track, the same mental file will come to host new information gained via the subject’s contextually changing relation to the wasp. For example, at t 1 the subject observes that the wasp is F, and at t 2 , seeing it again, she observes that it is G. The mental file stores both items of information (and TC is possible). The successive perceptual acts P1 and P2 are distinct, but the mental file remains numerically the same, and this embodies the subject’s presupposition that one and the same entity is being tracked throughout. Note that, at t 2 , the subject does not merely perceive the wasp, as she did at t 1 ; she also remembers the wasp seen at t 1 , so the relation to the wasp at t 2 involves both perception (P2) and memory (M). In other words, the same mental file, based on P1 at t 1 , is based on M + P2 at t 2 , yet it remains numerically the same mental file. That is why I spoke of a ‘contextually changing relation’ to the wasp. The fact that the mental file remains the same despite the relational change in question corresponds to the idea of a dynamic mode of presentation persisting through lower-level changes.

If the subject loses track of the wasp, then when she encounters it again at t 2 she will not store the information gained through P2 in that same mental file, but will open a new mental file based on P2. File duplication here embodies the lack of the presupposition of identity corresponding to the continued deployment of the same mental file. The subject may well conjecture that the two wasps are (probably) the same: unless the identity is presupposed and unreflectively taken for granted, the second perceptual encounter will give rise to a new file-opening event.

Let us now turn to the question: when (and why) is a mode of presentation based on a memory M the same dynamic mode of presentation as the mode of presentation based on the perception P from which the memory derives? A tentative answer in terms of mental files can be offered. The perception P launches a mental file which stores information gained through the perceptual relation. When the object gets out of sight, the thinker’s relation to the reference evolves: the subject remembers it instead of perceiving it. As long as the memory is ‘anchored’, i.e. associated with the body of information initially derived from the perception , this guarantees the persistence of the (dynamic) mode of presentation. Sometimes, however, an episodic memory occurs to the subject ‘unanchored’, i.e. dissociated from the mental file launched by the perceptual event from which the memory derives. Footnote 6 If, in such conditions, the subject wants to think about the reference of the free-floating memory, she has to open a new mental file for whatever it is she is remembering . For example, suppose the thinker has an isolated memory about a long-haired student with an accent, without having any idea who the student in question was, where and when she met him, etc. She will then think of him as ‘that student’, where this corresponds to a semi-descriptive mode of presentation based on the unanchored memory: ‘that student’ here means the student from which this memory derives . If, after a memory search, the subject eventually remembers who the student was, she will re-connect the memory with the mental file initially launched by the perceptual event. The memory will be (re-)anchored, and that will enable the subject to get rid of the new, semi-descriptive mental file and think of the student through the old file.

The answer to the question, then, is this. A mode of presentation based on an anchored memory is the same dynamic mode of presentation as the mode of presentation based on the perception from which the memory derives. (That is the normal case.) A mode of presentation based on an unanchored memory is distinct from the mode of presentation based on the perception from which the memory derives. What guarantees the unity of a dynamic mode of presentation despite the lower-level differences constituted by the changing relations to the reference is the body of information (the mental file) which is normally preserved and transmitted from perception to memory.

A referee has offered an alternative construal of the case I have just discussed. Instead of contrasting the two types of memories in terms of whether or not they are associated with the mental file initiated by the perception from which the memory derives, the referee says we should construe both types of memory as ‘anchored’, that is, as associated with a mental file stemming from the perceptual event the memory originates from. What distinguishes the allegedly ‘unanchored’ memories is the fact that ‘the thinker’s recollections have been fractured, i.e. the thinker recollects some things but not others’. For example, the thinker recollects that the remembered individual was a student, had an accent, had long hair, but not who he was nor where she met him etc. But then, the referee points out,

If the thinker recollects some things about the student but not others, it means that she presently has two memory files M1 and M2, both anchored in her past perception P, though one of the memory files is more anchored because most of the information from P is there and only little information is in the other.

On this construal there is a continuum of cases (some memories are more anchored than others) rather than a dichotomy between anchored and unanchored memories; so we can’t use the dichotomy to answer the question: when is a mode of presentation based on a memory M the same as the mode of presentation based on the perception P from which the memory derives, and when is it not ?

But I want to maintain that the dichotomy exists, and I propose to cash it out in phenomenological terms. A free-floating (unanchored) memory comes with a ‘metacognitive feeling’, akin to that involved in the famous tip-of-the-tongue phenomenon. Footnote 7 That feeling, which I take to be characteristic of unanchored memories, is that of having lost access to the associated mental file . That feeling triggers, on the part of the thinker, a search which gives rise to questions such as: ‘who is/was that student?’ Since the mental file launched by the perceptual event from which the memory derives is inaccessible, it cannot be deployed to think about the student in framing the question. Rather, the subject thinks about the student via a special-purpose mental file which, as Evans puts it, individuates its object ‘by its role in the operations of the informational system’ (Evans, 1982 : p. 128): the object of inquiry is thought of as that which the memory is a memory of . This semi-descriptive mode of presentation corresponds to a temporary mental file which is bound to disappear as soon as the missing mental file is retrieved (assuming it ever is).

This is not to deny that there may be cases of confusion in which, as the referee suggests, a perceptual event gives rise to two distinct memory files, both of which inherit (part of) the content of the perceptual file. Footnote 8 Such cases would be cases of ‘fission’, where the successor to the mental file initially launched by the perceptual event is not a single memory file but a pair of files, as if there had been two distinct events. Footnote 9 But this is not the phenomenon I am talking about in this section.

9 Conclusion: revisiting the criterion of difference

In this paper I have suggested a couple of revisions to the standard criterion of difference for modes of presentation attributed to Frege. First, we need to broaden the scope of the criterion so that not merely the thoughts of a given subject at a given time may or may not involve the same way of thinking of some object, but also the thoughts of a subject at different times. To that effect, borrowing from earlier work of mine, I put forward a dynamic variant of the criterion of difference:

m and m’ are distinct modes of presentation if the following conditions are satisfied: it is possible for a subject to believe of a given object, thought of under m , that it is F, and at a later time to hold a conflicting attitude (e.g. disbelief) toward the thought that results from substituting m’ for m in the initial thought; that is possible without change of mind on the subject’s part.

Using that variant, we can establish that the yesterday -mode of presentation and the today -mode of presentation are distinct modes of presentation, thanks to Burge’s observation that.

To be sure, only a temporally confused subject can, on a certain day, believe what is expressed by ‘Today is Friday’ and the following day, without changing their mind, doubt what is expressed by ‘Yesterday was Friday.’ if the subject has ‘kept track of time’ that epistemic possibility is ruled out. But this does not matter if one interprets the criterion of difference in the absolute way, as is standardly done. According to the absolute interpretation, the epistemic possibility invoked by the criterion of difference must only be a possibility for some rational subject (here, the confused subject); it need not be an epistemic possibility for every rational subject, not even for the particular subject whose thought is undergoing analysis. Just as a subject who knows that Hesperus is Phosphorus cannot, without irrationality, ascribe contradictory properties to Venus thought of as ‘Hesperus’ and to Venus thought of as ‘Phosphorus’, a subject who has kept track of time cannot, without changing their mind, doubt what is expressed by ‘Yesterday was Friday’ if the previous day they accepted ‘Today is Friday’. Still the fact that some rational subject might ascribe contradictory properties in this manner suffices to establish that the modes of presentation are different (even for the enlightened subject we are considering).

The second revision I advocated consists in giving up the absolute interpretation in favour of a different interpretation of the criterion of difference (one initially put forward by John Campbell): the ‘relativized’ interpretation. According to that interpretation, the epistemic possibility invoked by the criterion of difference must be compatible with the actual dispositions of the situated subject we are considering . The fact that the possibility evoked by Burge is ruled out if the subject has kept track of time means that, for that subject (in contrast to the temporally confused subject), the modes of presentation associated with ‘today’ and ‘yesterday’ are the same.

In this framework, a subject who knows that a  =  b (e.g. that Hesperus is Phosphorus, or that the seen banana is the touched banana) thinks of the referent under a composite mode of presentation, based on several epistemically rewarding relations to the reference simultaneously. The Hesperus/Phosphorus mode of presentation is such a composite mode of presentation, as is the visuo-tactile mode of presentation of the banana. These complex modes of presentation are distinct from ‘simple’ modes of presentation such as the Hesperus and the Phosphorus modes of presentation, or the visual mode of presentation and the haptic mode of presentation in the banana case.

By adopting the relativized interpretation of the criterion of difference, and the distinction between simple and complex modes of presentation, we can make sense of Evans’ notion of a dynamic mode of presentation that persists through time despite lower-level changes (Evans, 1981 , 1985 ). A dynamic mode of presentation is a complex mode of presentation based on several epistemically rewarding relations to the reference successively. I have shown how this idea can be cashed out in the mental file framework, and how, in that framework, we can provide a straightforward answer to the question: when is a mode of presentation based on a memory M the same as the mode of presentation based on the perception P from which the memory derives? The answer appeals to the distinction between anchored and unanchored memories.

In closing, I would like to mention the possibility of retaining the standard (‘absolute’) interpretation alongside the relativized interpretation of the criterion of difference, instead of construing them as exclusive of each other. (See Recanati, 2016 : pp. xiv–xvii for an early suggestion to that effect.) First, however, we need to distinguish between modes of presentation construed as types, as tokens, and as occurrences.

Token modes of presentation are the modes of presentation actually deployed in the thought of a particular, situated subject. The same token mode of presentation may be deployed several times by the subject in thinking of a given object, as in the instances of coreference de jure I mentioned earlier. In a train of thought such as that expressed by the anaphora-involving discourse ‘Roderick is F; he is G’, there are two occurrences of the same (token) mode of presentation, associated both with the antecedent name and with the anaphoric pronoun. The relativized version of the criterion of difference applies to token modes of presentation: two occurrences count as distinct token modes of presentation, rather than as occurrences of the same token mode of presentation, if the subject in whose thought they occur could, without changing her actual epistemic dispositions (and, in particular, her presuppositions), ascribe contradictory properties to the object respectively thought of under these modes of presentation.

Now, token modes of presentation are tokens of a certain type; for example, the token mode of presentation deployed twice by the subject in [TC-banana] is a token of a composite type, based on both vision and touch. When it comes to types (as opposed to tokens) the criterion of difference applies in its standard, unrelativized interpretation. Two modes of presentation m and m’ count as distinct types if some subject or other could (without irrationality, or without changing her mind in the diachronic cases) ascribe contradictory properties to some object respectively thought of under tokens of these modes of presentation. In this framework we can maintain that e.g. the today -mode of presentation and the yesterday -mode of presentation are two distinct types of mode of presentation, while acknowledging that, in the mind of a subject who has kept track of time, the same token mode of presentation is expressed by the subject’s use of ‘today’ on a certain day and by his use of ‘yesterday’ on the following day.

Evans credits Benacerraf for this observation. I am indebted to Matheus Valente and Victor Verdejo for drawing my attention to that important footnote.

The idea that the relevant subject is ‘some subject or other’ corresponds to what I call the absolute interpretation of the criterion of difference. It contrasts with another possible interpretation, to be argued for in Sect. 5: the relativized interpretation. According to the relativized interpretation, two coreferential expressions ‘ a ’ and ‘ b ’ are associated with distinct senses for some particular subject if that subject could assent to ‘ a is F’ and simultaneously withhold assent from, or reject, ‘ b is F’. Here the relevant subject is not ‘some subject or other’ but a particular subject in a particular epistemic situation.

As a reviewer pointed out, it might be more appropriate to call them memory demonstratives, in order to make room for a distinction between memory tenseless judgments (e.g. ‘that man was a philosopher’) and memory tensed judgments (e.g. ‘that man was drenched’): both involve memory demonstratives, the reviewer suggests, but the former are ‘less temporal’ than the latter (so the memory demonstratives they involve don’t deserve the label ‘past-tense demonstrative’). I leave that issue aside and refer the interested reader to Campbell 2002 , chapter 6, where the relevant distinctions are drawn.

See Recanati (forthcoming) for a critical discussion of Ninan’s argument.

Perception, memory, testimony count as epistemically rewarding relations, as do indexical relations such as the relation you hold to a place when you occupy that place, or the relation in which you stand to an individual when you are that individual. See Recanati ( 2012 , 2016 ).

Speaking of ‘the’ perceptual event from which the memory derives presupposes that a memory has a unique perceptual antecedent. As the lead guest editor of this issue pointed out, that presupposition has been questioned (Debus 2007 , Liefke forthcoming 2021 , Openshaw 2022 ), on the grounds that not all experiential remembering is ‘episodic’ and concerns a unique, specific event: some memory representations (in particular, memory representations of individuals) are built up by repeated exposures over time. Here, however, I am only concerned with genuinely episodic memories. (According to Perrin et al. ( 2020 ), episodic memories are distinguished by a specific phenomenological feature which they call ‘the feeling of singularity’. As they put it, ‘episodic memories (…) typically represent singular events (…). So, it seems important to include singularity among the components of the content of episodic memory. The content of many episodic memories is formed of an imagistic content plus a certain phenomenology. (…) Our suggestion is that the singularity feature of remembered events can be conveyed by phenomenology’ (Perrin et al., 2020 : p. 4).).

On metacognitive feelings, see e.g. Koriat ( 2000 ), ( 2007 ), Proust ( 2007 ), ( 2013 ), de Sousa ( 2009 ), Dokic ( 2012 ).

The two memory files M1 and M2 evoked by the referee in reinterpreting my ‘student’ example are such that only one of them is consciously accessible; while the case of confusion I am now evoking would be a case in which the two distinct memory files at stake are both consciously accessible.

The possibility of such cases invoving fission shows that dynamic ‘sameness’ is not identity in the strict, Leibnizian sense (Recanati 2016 : 84–86): the twin memory files which result from ‘splitting’ the initial file launched by the perceptual event cannot both be identical to that initial file, since they are distinct from each other. Leibnizian identity is transitive but, as in the case of personal identity (see Prosser 2019 for the analogy), the relation of dynamic continuity seems not to be. (We can restore transitivity, hence a strict reading of ‘same dynamic mode of presentation’, by explicitly ruling out cases of fission.).

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Acknowledgments

I am indebted to John Campbell, Michael Murez, James Openshaw, Matheus Valente, Jean-Baptiste Rauzy, and two reviewers for their helpful comments.

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Recanati, F. Memory-based modes of presentation. Synthese 203 , 116 (2024). https://doi.org/10.1007/s11229-024-04531-0

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Types of Long-term Memory

Aug 28, 2014

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Types of Long-term Memory. Explicit memory. aka Declarative or Conscious memory Memory consciously recalled or declared Can use explicit memory to directly respond to a question Two subtypes of explicit memory. Subtypes of Explicit Memory. Episodic memory.

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Explicit memory • aka Declarative or Conscious memory • Memory consciously recalled or declared • Can use explicit memory to directly respond to a question • Two subtypes of explicit memory

Subtypes of Explicit Memory

Episodic memory • Memory tied to your own personal experiences • Examples: • What month is your birthday? • Do you like to eat caramel apples? • Q: Why are these explicit memories? • A: Because you can actively declare your answers to these questions

Semantic memory • Memory not tied to personal events • General facts and definitions about the world • Examples: • How many tires on a car? • What is a cloud? • What color is a banana?

Semantic memory • Q: Why are these explicit memories? • A: Because you can actively declare your answers • Important note: Though you may have personal experience with these items, your ability to answer Q’s does NOT depend on tying the item to your past • i.e. Do not have to recall the time last week when you ate a banana to say that bananas are yellow

Implicit memory • Aka nondeclarative memory • Influences your thoughts or behavior, but does not enter consciousness • Three subtypes

Subtypes of Implicit Memory

Natural reflex Neutral stimulus + UCS (food in mouth) (ringing bell) UCR (salivation) Conditioned reflex CS (ringing bell) CR (salivation) Classical conditioning • Pavlov • Previously neutral stimulus now comes to elicit a response after pairing with an unconditioned stimulus

Procedural memory • Memory that enable you to perform specific learned skills or habitual responses • Examples: • Riding a bike • Using the shift stick while driving • Tying your shoe laces • Q: Why are these procedural memories implicit? • A: Don’t have to consciously remember the steps involved in these actions to perform them • Try to explain to someone how to tie a shoelace

Priming • Pass out demonstration sheets

Priming demonstration • Unscramble the following word: • L T E P A • Answer: • P E T A L • P L A T E

Priming • Why did half the class say plate and the other half say petal? • They were primed to do so • There were two different sheets of unscrambled words

Priming sheet 1 • Unscramble the following word: • F I N E K • O P O N S • K R O F • P U C • E C U S A R • L T E P A • Answer: • K N I F E • S P O O N • F O R K • C U P • S A U C E R • P L A T E

Priming sheet 2 • Unscramble the following word: • N Y P A S • F E L A • K T A L S • D U B • L O B S O M S • L T E P A • Answer: • P A N S Y • L E A F • S T A L K • B U D • B L O S S O M • P E T A L

Priming • Do priming demonstration

Seeing the word rabbit Activates concept Primes spelling the spoken word hair/hare as h-a-r-e Priming

Priming • Activation of one or more existing memories by a stimulus • Activation not a conscious decision • BUT, can effect subsequent thoughts and actions • Two types of priming

Two types of priming

Conceptual priming • When priming stimulus influences your flow of thoughts • Thought to involve activation of concepts stored in semantic memory • Example: Previous priming demonstration • Example: If you hear a story about a pitbull, when someone later asks you to name a dog, you’re more likely to say “pitbull”

Perceptual priming • Can you identify the fragmented stimulus below?

Perceptual priming • What if you were shown the following slide earlier in the lecture?

Perceptual priming • Can you identify the fragmented stimulus to the right?

Perceptual priming • When a priming stimulus enhances ability to identify a test stimulus based on its physical features • Priming is implicit because you don’t need to consciously recall seeing the priming stimulus in order for priming to occur

Evidence for separate implicit/explicit systems? • Neurophysiological evidence • Patient H.M. • Life-threatening seizures originating in temporal lobe • surgically removed portions of temporal lobe

Temporal lobe Hippocampus Temporal lobe • Includes: • hippocampus • amygdala

Patient H.M. • surgery was effective in reducing seizures • BUT, had other side effects as well • Can remember explicit memories acquired before the surgery • e.g. old addresses, normal vocabulary • Had difficulty forming NEW explicit memories • e.g. remembering the name of someone he met 30 minutes prior • cannot name new world leaders or performers

Hippocampal damage • Deficits in forming new explicit memories

Temporal lobe damage • Monkeys and rodents with temporal lobe damage show similar patterns of deficits • Impaired performance on a delayed-nonmatch-to-sample task that tests explicit memory

DNMTS task Delay Sample Phase Choice Phase

Temporal lobe damage • Not impaired on similar task that taps habit-based (implicit) memory

Habit-based task task Trial One Trial Two

Patient H.M. Summary • Temporal lobe damage led to deficits in explicit, but not implicit memory • H.M. had both episodic and semantic memory deficits • Damage to the hippocampus alone produces episodic, but not semantic memory deficits • Why did H.M. show both types of explicit memory deficits? • He had damage not only to hippocampus, but to other structures as well

Are memories organized? • Demonstration: • Recite the days of the week • Recite the days of the week in alphabetical order • Demonstrates that long-term memory is organized • not just a random jumble of information • How are memories organized?

Demonstration • List of words will be read one at a time • Recall as many words as possible

Demonstration • Look at your sheet • Is there a pattern to your answers? • Most list several fruits, then vehicles, then furniture (or vice versa)

How are memories organized? • Hierarchical organization • Associations

Hierarchical organization • Related items clustered together to form categories • Related categories clustered to form higher-order categories • Remember list items better if list presented in categories • poorer recall if presented randomly • Even if list items are random, people still organize info in some logical pattern

Hierarchical organization

Spreading activation model • Mental links between concepts • common properties provide basis for mental link • Shorter path between two concepts = stronger association in memory • Activation of a concept starts decremental spread of activity to nearby concepts

Car Bus Truck Fire Engine House Ambulance Fire Red Hot Stove Rose Cherry Apple Pot Pan Violet Flower Pie Pear Spreading activation model

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