short term memory duration experiment

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• Simply Psychology - Short Term Memory
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short-term memory , in psychology , the concept involving the extremely limited number of items that humans are capable of keeping in mind at one time. Of undeniable importance, the long-standing concept of “short-term memory” is one of the most researched topics in cognitive science . Nearly every act of cognition —reasoning, planning, problem solving—relies on one’s ability to store and manipulate information.

The study of short-term memory was revolutionized by the experiments of British psychologist Alan D. Baddeley and his colleagues in the 1970s and ’80s. According to their model, short-term or “working memory” consists of at least two storage buffers: one for visuospatial information and another for verbal information. A unique aspect of their model was its inclusion of a “central executive” (also called “executive attention”) that coordinates the activities of the storage buffers and manipulates information. This newer concept of working memory can be likened to a mental workspace rather than a simple storage device or a conduit into “long-term memory.” The switch in terminology between short-term memory and working memory reflects this belief in the importance of using this mechanism for performing mental work.

Much recent short-term memory research has focused on three issues: (1) Are there truly separable stores for different types of information? (2) What is the nature of the central executive? (3) Do individual differences in short-term memory abilities account for different levels of ability to read, plan, and solve problems?

Research suggests that there are at least two distinct storage buffers: one for the verbal information and another for visuospatial information. Much of the evidence for this distinction comes from the logic of double dissociation . According to this logic, two cognitive mechanisms (e.g., verbal and spatial short-term memory) are separate if the task performance is differentially impacted by two different variables. For example, performance on verbal working memory tasks (e.g., remember a set of letters), but not spatial working memory tasks (e.g., remembering a set of locations on a computer screen), is impaired by having to say a syllable or word repeatedly (e.g., “the, the, the”) during a memory delay. This is presumably because having to repeat the word or syllable prevents people from silently rehearsing the to-be-remembered letters, a common tactic known as subvocal rehearsal. Conversely , being required to tap a set of computer keys in a spatial pattern interferes with memory for a set of locations in space, but not with memory for a set of letters. Taken together, this set of findings implies that verbal and spatial short-term memory rely on different pools of cognitive resources.

Psychologists Patricia A. Reuter-Lorenz and Andrea C. Miller used the logic of double dissociation to determine whether verbal and spatial short-term memory rely on different neural mechanisms by testing a patient who had undergone a callosotomy ( split-brain ) procedure. They found that when the verbal variant of the task was presented to the left hemisphere, performance was markedly superior to when the verbal task was presented to the right hemisphere. The opposite was true when the spatial task was presented to the right hemisphere. These findings were bolstered by data from neuroimaging and patient studies of the division between verbal and spatial information, which found that verbal tasks are mediated largely by left hemisphere neural regions, whereas the spatial task are relatively largely right lateralized.

In the original working memory model of Baddeley and Graham Hitch, the central executive was the least developed component, prompting a great deal of interest in trying to characterize this mechanism. Some researchers have proposed that it coordinates and controls various subparts of the system. Such a conceptualization is consistent with a number of different computational models, in that many major architectures contain a mechanism that determines whether goals and subgoals are being met and strategically schedules the initiation of various processes. Others have conceptualized executive function as a collection of processes that serve to manipulate the contents of working memory, including inhibition , attention , and temporal ordering.

One thing that appears to distinguish earlier ideas of short-term memory from working memory is that performance on tasks involving just the short-term storage of information does not predict how well people will perform on higher-order reasoning skills, whereas performance on tasks involving both the simultaneous storage and manipulation of information in memory predicts a host of cognitive skills. For instance, it has been shown that working memory capacity, as defined by the ability to simultaneously store and process information, predicts reading comprehension skill. Working memory capacity also predicts how well people will perform on problem-solving tasks, such as conditional reasoning problems. Thus, it appears that working memory capacity can account for many of the skills that constitute intelligence.

From a developmental perspective, working memory is critical because it may play a role in learning language , particularly in vocabulary acquisition. Furthermore, just as working memory capacity can predict performance on higher-order cognitive tasks, working memory ability has been hypothesized to play a role in diverse childhood and adult maladies such as attention deficit hyperactivity disorder, mathematical disabilities, and reading disabilities. Furthermore, children of school age in cultures in which the articulation time to numbers or letters is shorter (e.g., Chinese, as compared with German) show a greater memory capacity earlier in development. This is because verbal memory is language-based and limited not just by the number of items but also by how long it takes to utter them.

Just as important cognitive skills appear to develop with the help of working memory in childhood, working memory declines in older adults appear to be a factor in age-related changes in a range of cognitive tasks. Adults reach their peak working memory capacity in their twenties, conveniently coinciding with the college years for many, then decline steadily over the life span into old age .

AS Psychology

Peterson and peterson (1959) – stm.

Aim – To investigate the duration of short term memory and provide empirical evidence for the multi-store model

Procedure – An experiment was conducted in which 24 participants had to recall trigrams (three consonant syllables). They were asked to recall trigrams after intervals of 3, 6, 9, 12, 15 or 18 seconds.

Results – The longer the interval delay the less trigrams were recalled. Participants were able to recall 80% of trigrams after a 3 second delay. However, after 18 seconds less than 10% were able to recall the trigrams correctly.

Conclusion – Short-term memory has a limited duration when rehearsal is prevented. It’s believed that the information is lost from short-term memory from trace decay.

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Short-Term Memory

Experiments.

Before continuing, do the experiment your instructor assigned ( or ). If your instructor did not specify one, do . Either experiment will take about 15 minutes.

After doing that experiment, click to continue .

Explanation

If you did , you now know that you actually did a learning experiment rather than a simple memory test. Your performance was probably much better than chance, showing that you learned the string-generation rule to some extent. Most people get 70-80% of the test items correct, while they would only get 50% correct if they had learned nothing of the rule. This is called “implicit learning” (Reber, 1967; Reber and Lewis, 1977).

If you did , you were told at the outset that your task was to learn the rule that generated the strings you were given. In general, those who try to actively learn this rule do worse than those who learn it passively.

It should come as no surprise that we are good at learning grammatical rules passively, simply by seeing examples. That is, after all, how we learn language. Why is it more difficult to learn the patterns explicitly? Perhaps attempting to learn the pattern inhibits the specialized mechanisms we have for learning grammar and instead relies on cognitive mechanisms that are less efficient at this task but better for more general purposes.

After completing all experiments in this section (including the Further Explorations below), see for explanation of the rule that generated these strings. This is a “generative grammar,” which may be familiar if you have taken mid-level computer science classes. As such grammars go, it is not very complex, but you can see that it would be difficult to reconstruct it from the strings you were given.

Further Exploration

• After a day or two, test how well you retained what you learned in this experiment. Use one of the following, depending on the stimulus set that you were given in the experiment (if you do not remember the stimulus set, open the data file you produced; it will show the stimulus set).
• If your class is large and was split between groups doing and , do a statistical analysis of the results. Is each group’s performance significantly above 50%? Are the two groups significantly different?
• Does knowing that the task in is actually a learning task affect your performance if you repeat the experiment with a different grammar set? Try the learning test again, this time specifying a stimulus set. Determine which stimulus set you used originally (see Exploration #1) and choose an experiment that uses a different set.
• Can you think of cases other than language in which implicit learning takes place? How would you test these cases experimentally?
• How would you expect an amnesic patient (e.g. the well-known HM) to fare on this task?
• Reber AS (1967). Implicit learning of artificial grammars. J. Verbal Learning & Verbal Behavior 6:855-863.
• Reber AS, Lewis S (1977). Implicit learning: An analysis of the form and structure of a body of tacit knowledge. Cognition 5:333-361.

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Short Term Memory ( AQA A Level Psychology )

Revision note.

Short Term Memory Capacity & Duration

What is short-term memory.

• Short-term memory (STM) has the ability to hold a small amount of information for a relatively short period of time
• The amount (capacity) and duration of STM is greater than sensory memory but smaller than long-term memory
• It is seen more as a holding device before memory is forgotten/lost or moved to long-term memory

What is the capacity of STM?

• Experiments conducted by Miller (1956) indicate the capacity of STM is 7 items or chunks plus or minus 2 (5-9 items)
• Miller demonstrated this in an experiment where he asked participants to recall information, adding an extra bit as he moved on: A bit like the game ‘I went to the shops’
• Starting participants with two or three words to recall, he gradually built it up until they made an error
• It was found that most participants struggled with between 5-9 words
• This is known as ‘Miller’s Magic 7’

How can we evaluate research into capacity and STM?

• Jacobs (1887) had completed a similar experiment using digits with 443 female students
• He called this a digit span experiment, using numbers instead of words
• His results were similar to Miller's , with 7.3 being the average recall
• This supports Miller and suggests his study is valid
• Miller’s study is also reliable as it is easy to copy and it is especially reliable as the results are more often than not the same
• As it is a lab study extraneous variables would have been controlled
• However, it could be argued it lacks ecological validity as the task bears little resemblance to real life

Short-term memory duration

• Duration relates to how long a memory can be stored for
• As short-term memory (STM) is only a temporary device, then this is limited
• The duration of short-term memory is around 18-30s

Evidence for the duration in short-term memory

• The main study into duration and STM comes from Peterson and Peterson (1959)
• They gave participants non-sensical three-letter trigrams to learn eg. CGR or BHT
• These were presented visually to the participants, one at a time
• The participants had to recall the trigram in the correct order after a delay of either 3s, 6s, 9s, 12s, 15s or 18s
• During this delay they were asked to complete a distraction task: usually counting backward from 300 in 3s (300, 297,294 etc.)
• This was to prevent them from rehearsing during the delay
• A graph of the correctly recalled trigrams over time was plotted and was shown to be a decay curve
• This demonstrates that over time the memory seems to decay
• The graph was extrapolated to show that after the 30s recall in STM would be zero
• Therefore, Peterson and Peterson stated that the duration of STM was 18-30s

Evaluation of duration in short-term memory

• Peterson and Peterson conducted a well-controlled study and many extraneous variables would have been removed or controlled for
• But does it prove decay?
• Could it be that previous trigrams, maybe similar to the one being recalled, interfered with the memory and that is why the participant made the mistake?
• This challenges the validity of the study

For the duration of Short Term memory, you need to be in the correct 'ball park' in terms of numbers. The examiner will accept anything from 15-30s (they may be even more generous some years) but anything looking at minutes will be marked as incorrect.

Short Term Memory Encoding

What is encoding in short-term memory.

• Encoding is how the information is processed from the senses into the memory itself
• This is how the information will be stored and ultimately recalled
• Encoding is always in the form of a modality or one of the senses
• Short-term memory encodes acoustically or using sound

What is the evidence for acoustic encoding in short-term memory?

• We know this from a study by Baddeley (1966)
• Baddeley considered encoding in short-term memory and long-term memory but here we will look at STM only
• Acoustically similar: words that sounded the same such as cat, bat, rat
• Acoustically dissimilar: words that did not sound the same such as laugh, bear, pencil
• Semantically similar: words that mean the same such as large, huge, enormous
• Semantically dissimilar: words that do not mean the same such as police, computer, chair
• The words were all presented visually, on a screen as part of a slideshow
• They had to be recalled in the order presented: Free recall was not allowed
• For the short-term part of the experiment, he asked for a recall immediately
• He found the acoustically similar words had the worst recall
• There was no difference in STM for the semantically similar and dissimilar words
• From this, he concluded that STM relied on acoustic encoding to process information

How can we evaluate the research into encoding in STM?

• Once again, this is a lab experiment so is highly controlled, with extraneous variables taken care of
• However, this also means that it lacks ecological validity as the tasks do not relate to real life
• The words had little to no meaning for participants and so they were harder to recall
• Information we have to recall in reality often has meaning and significance so making recall easier

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Author: Emma rees

Short Term Memory

There are two places where we store memories. Most of our memories are stored in our long-term memory. (You can watch a video all about this limitless memory storage in another video.) In this video, we are going to focus on short-term memory storage.

This storage has limits, and in some cases, can be completely obliterated. But research on short-term memory has given scientists important information on how we store and process memories, as well as ways that we can improve our ability to remember information.

Let’s get started.

What is Short Term Memory?

Short Term Memory refers to the ability to hold a small amount of information in your mind for a short period of time. Two important qualities of short term memory are that you can't manipulate the information (unlike working memory) and it doesn't last for more than 18 seconds.

Looking to test your short-term memory for free? Check out our free memory test and find your results in less than 5 minutes!

Our short-term memory storage goes through a lot of disposals. We can only remember things short-term for so long! But how much information can you store in your short-term memory, and how long will information last in this part of your memory storage?

The exact numbers vary for everyone, but research on short-term memory has given us a good estimate of the average duration and capacity of short-term memory storage.

What's the Capacity?

In the world of psychology, the “magic number” of items that you can store in your short-term memory is “Seven, Plus or Minus Two.” This magic number is based on a paper written by American psychologist George Miller. There are ways to “hack” this capacity, but we will talk about it later in the article.

How long does Short Term Memory last?

Short Term Memory lasts around 18 seconds, however, you can stretch this duration out to 30 seconds or more if you actively rehearse or repeat the items in your head. If you make no effort to remember these items, they will disappear in a manner of seconds.

​ You can only keep seven (plus or minus two) items in your head for so long. Some studies suggest that this 30-second duration can extend up to one minute, but for most people, 30 seconds is the limit.

There are multiple theories that explain why pieces of information leave our short-term memory storage. In this video, we’ll talk about how distraction and interference might take over, or the information simply “decays.” The best method to remember what's in your short-term memory is to store it in your long-term memory.

Decay Theory

Why do we forget? Why do pieces of information leave our short-term memory after a period of time?

One of the explanations is the Decay Theory or the Trace Decay Theory of Forgetting. This theory is relatively simple; it states that memories decay over time. When the memory is initially created, it leaves a “trace” of chemical changes in the brain. As time passes, that trace fades away.

On one hand, this theory is perfectly sensible. We are more likely to remember a phone number told to us two minutes ago than a phone number that was told to us two weeks ago. We are likely to remember what we ate yesterday, but less likely to recall anything significant from a specific date four years ago.

...in most cases.

This theory has been disputed, partly because people do have such strong memories of events from certain dates and events in their lives. People may recall significant (or seemingly insignificant) pieces of information from a long time ago, but may not remember what they ate for breakfast. Not all memories just fade away. Here is a graph that shows how much of a list is retained during a 'relearning' process:

This theory is not easy to test and prove, partially because it’s hard to control for repetition and distraction.

Displacement and Distractions

Let’s go back to the idea that you might remember what you had for breakfast yesterday, but not what you had for breakfast two years ago. There is a lot that happened between two years ago and yesterday. You had over 600 breakfasts, 600 lunches, 600 dinners.

You were asked to remember phone numbers and study for tests and make mental notes of your best friend’s birthday. Even if you tried your hardest to remember what you had for breakfast on a specific date, there are so many things to distract you from that memory.

This is another theory that tries to explain why we forget things. We displace previous memories with other memories.

Serial Position Effect and Recency Theory

One study to support this theory has also contributed to the Serial Position Effect and Recency Theory . In the study, researchers gave participants a list of information to memorize. The participants were separated into two groups. The first group recalled the items immediately. The second group was given a distraction task to complete for a few seconds before being asked to recall the information.

The results from both groups supported the Serial Position Effect: the information at the beginning and the end was more likely to be recalled by participants. However, the group who completed the distraction tasks were much less likely to recall the items at the end of the list.

Those items were stored in short-term memory, but with distractions, they were displaced quickly.

Do you like to multi-task?

The displacement theory is one piece of evidence that supports the idea that multi-tasking isn’t so productive.

Each new task that you refer back to is a distraction . The meme you saw on Facebook is likely to interfere with storing information that you are trying to study. This constant distraction and displacement of memory can potentially affect your ability to store information long-term.

Anterograde Amnesia (Short Term Memory Loss)

We can’t talk about short-term memory storage without talking about our favorite fish that...doesn’t have short-term memory. Yes, I’m talking about Dory. Dory’s most unique characteristic was her inability to hold onto information for more than a few seconds. While comical, it has lead many people to wonder...is short-term memory loss a real condition?

It is! It’s called Anterograde Amnesia.

Anterograde amnesia is a condition in which people develop a partial or complete inability to recall the recent past. Memories are created, but often immediately forgotten or decayed. Even after five seconds, a person with anterograde amnesia cannot recall something that was just said to them.

What Causes Short Term Memory Loss?

How does one develop Anterograde Amnesia? There are a few ways:

• Benzodiazepine drugs (also known as “benzos”)
• Too much alcohol (also known as a “blackout”)
• Traumatic brain injury
• Emotional disorders
• Illnesses that cause neurological deterioration

Can You Restore Short Term Memory?

Memories must be converted to long term memory if we want to recall them later in life. Yes, you may remember something that you thought you had forgotten a long time ago. Those memories were hidden somewhere in your long term memory. Information from our short term memories, if not converted, are lost forever. That’s why you might have to piece together your wild night out with the help of other people whose memories were converted to long-term memory. 

Short-term memory loss can be terrifying. There is no cure for short-term memory loss if it’s the result of a disease like Parkinson’s or Alzheimer’s. However, there are ways that you can slow the effects of short-term memory loss and keep your memories intact. 

• Getting 8+ hours of sleep every night 
• Eating a healthy diet with Omega-3 supplements
• Completing puzzles, playing instruments, or doing other activities that challenge the brain 
• Organizing information like everyday tasks on to-do lists 

Other ways to slow short-term memory loss may depend on what is causing the short-term memory loss in the first place. If a medication, tumor, or mental health condition is causing memory loss, different treatments can help slow its progress. If you are concerned about your short-term memory, consider reaching out to your primary care doctor for a proper assessment.

Fortunately, research on long-term memory storage is making progress . Some believe that if the connections between certain synapses can be restored, so can long-term memories!

Can You Increase Short Term Memory?

We all know someone whose memory is spot-on. And we all know someone who...needs to write everything down. Memory is a good thing to have! A lack of short-term memory can be embarrassing, or even dangerous. But are there ways to train your brain to remember more things in a short period of time?

The answer is yes!

You now know that your short-term memory storage is limited. The brain can only keep 5-9 items in your short-term memory at a time. But there’s a way to “hack” this limit and retain more information in your short-term memory for a longer period of time. This hack is called “chunking.”

Chunking just requires that you “chunk” multiple pieces of information together to form a single group of items to remember. While the brain can store only 5-9 pieces of individual information, research shows that you can store up to four chunks of information. If each chunk has four pieces of information attached to it, you can hack your way into recalling 16 things that you need to remember.

One of the most common examples of chunking is memorizing phone numbers. Memorizing ten individual numbers at a time is no easy task. But when you separate things into three chunks (the area code, the first three numbers, and the last four numbers,) remembering that phone number is entirely possible.

Other Ways to Improve Short-Term Memory

Chunking can be used alongside other memory “hacks” that expand your ability to store more items in your short-term memory. These hacks include memory tricks, like:

• Other mnemonic tricks

I’ve got a whole video on these different tricks that you can watch!

Short Term Memory Tests

Want to test out your short-term memory storage? Use the following links to test out your memory:

• Short-Term Memory Test from University of Washington
• DIY Test from VeryWellMind
• Short-Term Memory Quiz on The Mirror

We are still a long way from completely understanding how short term memory works, and what we can do to prevent forgetting and displacement. The best solution seems to be storing short term memory in long term memory.

There are also other forms of memory, including working memory and long-term memory , which cognitive scientists have studied for years trying to figure out.

This article aims to be the best of the best at teaching young psychology students everything there is about short term memory, so if you think I missed something, or you found some new research that's relevant, please leave a comment below!

Related posts:

• Free Memory Test (5 Mins + Instant Results)
• Atkinson and Shiffrin Model of Memory (Multi-Store Model)
• Memory (Types + Models + Overview)

Long Term Memory

• Sensory Memory (Definition + Examples)

Reference this article:

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Free Memory Test

Serial Position Effect

Primacy Effect

Recency Effect

Sensory Memory

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Episodic Memory

Semantic Memory

False Memories

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Memory Tricks

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Duration refers to how long a memory ‘trace’ (i.e. information about the past) can be held for, before it is forgotten.

According to Atkinson and Shiffrin’s multi-store model of memory, the duration of the Sensory Register (holding information taken directly from the senses) has a brief duration of just half a second.

Attending to and rehearsing information helps to retain information in Short-Term Memory for a duration of up to approximately 30 seconds, and consolidate it into Long-Term Memory.

The duration of Long-Term Memory is considered to be anything greater than 30 seconds – its maximum duration appears to be unlimited.

Research example :

Peterson and Peterson’s 1956 experiment is an early example of research providing insight into Short-Term Memory duration.

Participants were presented with nonsense trigrams (written strings of three consonants, e.g. XQF) and asked to recall them after 3, 6, 9, 12, 15, or 18 seconds.

However, to prevent participants from rehearsing trigrams during these pauses, they counted down in threes from a number set by the experimenters – this is known as an interference task.

The results found an 80% accuracy rate for trigram recall after 3 seconds, but only 10% accuracy after 18 seconds, suggesting that Short-Term Memory duration is limited to roughly 18 seconds when rehearsal is prevented.

Evaluation of Peterson and Peterson (1956):

• There is a good chance that the results are reliable (i.e. can be replicated) as variables can be closely controlled in a laboratory environment.
• However, the results possess low ecological validity (i.e. might not apply to real life), as nonsense trigrams are arguably unrealistic examples of the kind of information people learn on an everyday basis.
• Sensory Register
• Episodic Memory
• Working memory model
• Short-Term Memory

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What are the differences between long-term, short-term, and working memory?

Nelson cowan.

Department of Psychological Sciences, University of Missouri, 18 McAlester Hall, Columbia, MO 65211, USA

In the recent literature there has been considerable confusion about the three types of memory: long-term, short-term, and working memory. This chapter strives to reduce that confusion and makes up-to-date assessments of these types of memory. Long- and short-term memory could differ in two fundamental ways, with only short-term memory demonstrating (1) temporal decay and (2) chunk capacity limits. Both properties of short-term memory are still controversial but the current literature is rather encouraging regarding the existence of both decay and capacity limits. Working memory has been conceived and defined in three different, slightly discrepant ways: as short-term memory applied to cognitive tasks, as a multi-component system that holds and manipulates information in short-term memory, and as the use of attention to manage short-term memory. Regardless of the definition, there are some measures of memory in the short term that seem routine and do not correlate well with cognitive aptitudes and other measures (those usually identified with the term “working memory”) that seem more attention demanding and do correlate well with these aptitudes. The evidence is evaluated and placed within a theoretical framework depicted in Fig. 1 .

A depiction of the theoretical modeling framework. Modified from Cowan (1988) and refined in further work by Cowan (1995 , 1999 , 2005) .

Historical roots of a basic scientific question

How many phases of a memory are there? In a naïve view of memory, it could be made all of one cloth. Some people have a good ability to capture facts and events in memory, whereas others have less such ability. Yet, long before there were true psychological laboratories, a more careful observation must have shown that there are separable aspects of memory. An elderly teacher might be seen relating old lessons as vividly as he ever did, and yet it might be evident that his ability to capture the names of new students, or to recall which student made what comment in an ongoing conversation, has diminished over the years.

The scientific study of memory is usually traced back to Hermann Ebbinghaus (1885/1913 translation) , who examined his own acquisition and forgetting of new information in the form of series of nonsense syllables tested at various periods upto 31 days. Among many important observations, Ebbinghaus noticed that he often had a “first fleeting grasp … of the series in moments of special concentration” (p. 33) but that this immediate memory did not ensure that the series had been memorized in a way that would allow its recall later on. Stable memorization sometimes required further repetitions of the series. Soon afterward, James (1890) proposed a distinction between primary memory, the small amount of information held as the trailing edge of the conscious present, and secondary memory, the vast body of knowledge stored over a lifetime. The primary memory of James is like the first fleeting grasp of Ebbinghaus.

The Industrial Revolution made some new demands on what James (1890) called primary memory. In the 1850s, telegraph operators had to remember and interpret rapid series of dots and dashes conveyed acoustically. In 1876, the telephone was invented. Three years later, operators in Lowell, Massachusetts started using telephone numbers for more than 200 subscribers so that substitute operators could be more easily trained if the town’s four regular operators succumbed to a raging measles epidemic. This use of telephone numbers, complemented by a word prefix, of course spread. (The author’s telephone number in 1957 was Whitehall 2–6742; the number is still assigned, albeit as a seven-digit number.) Even before the book by Ebbinghaus, Nipher (1878) reported on the serial position curve obtained among the digits in logarithms that he tried to recall. The nonsense syllables that Ebbinghaus had invented as a tool can be seen to have acquired more ecological validity in an industrial age with expanding information demands, perhaps highlighting the practical importance of primary memory in daily life. Primary memory seems taxed as one is asked to keep in mind aspects of an unfamiliar situation, such as names, places, things, and ideas that one has not encountered before.

Yet, the subjective experience of a difference between primary and secondary memory does not automatically guarantee that these types of memory separately contribute to the science of remembering. Researchers from a different perspective have long hoped that they could write a single equation, or a single set of principles at least, that would capture all of memory, from the very immediate to the very long-term. McGeoch (1932) illustrated that forgetting over time was not simply a matter of an inevitable decay of memory but rather of interference during the retention interval; one could find situations in which memory improved, rather than diminish, over time. From this perspective, one might view what appeared to be forgetting from primary memory as the profound effect of interference from other items on memory for any one item, with interference effects continuing forever but not totally destroying a given memory. This perspective has been maintained and developed over the years by a steady line of researchers believing in the unity of memory, including, among others, Melton (1963) , Bjork and Whitten (1974) , Wickelgren (1974) , Crowder (1982 , 1993) , Glenberg and Swanson (1986) , Brown et al. (2000) , Nairne (2002) , Neath and Surprenant (2003) , and Lewandowsky et al. (2004) .

Description of three kinds of memory

In this chapter I will assess the strength of evidence for three types of memory: long-term memory, short-term memory, and working memory. Long-term memory is a vast store of knowledge and a record of prior events, and it exists according to all theoretical views; it would be difficult to deny that each normal person has at his or her command a rich, although not flawless or complete, set of long-term memories.

Short-term memory is related to the primary memory of James (1890) and is a term that Broadbent (1958) and Atkinson and Shiffrin (1968) used in slightly different ways. Like Atkinson and Shiffrin, I take it to reflect faculties of the human mind that can hold a limited amount of information in a very accessible state temporarily. One difference between the term “short-term memory” and the term “primary memory” is that the latter might be considered to be more restricted. It is possible that not every temporarily accessible idea is, or even was, in conscious awareness. For example, by this conception, if you are speaking to a person with a foreign accent and inadvertently alter your speech to match the foreign speaker’s accent, you are influenced by what was until that point an unconscious (and therefore uncontrollable) aspect of your short-term memory. One might relate short-term memory to a pattern of neural firing that represents a particular idea and one might consider the idea to be in short-term memory only when the firing pattern, or cell assembly, is active ( Hebb, 1949 ). The individual might or might not be aware of the idea during that period of activation.

Working memory is not completely distinct from short-term memory. It is a term that was used by Miller et al. (1960) to refer to memory as it is used to plan and carry out behavior. One relies on working memory to retain the partial results while solving an arithmetic problem without paper, to combine the premises in a lengthy rhetorical argument, or to bake a cake without making the unfortunate mistake of adding the same ingredient twice. (Your working memory would have been more heavily taxed while reading the previous sentence if I had saved the phrase “one relies on working memory” until the end of the sentence, which I did in within my first draft of that sentence; working memory thus affects good writing.) The term “working memory” became much more dominant in the field after Baddeley and Hitch (1974) demonstrated that a single module could not account for all kinds of temporary memory. Their thinking led to an influential model ( Baddeley, 1986 ) in which verbal-phonological and visual-spatial representations were held separately, and were managed and manipulated with the help of attention-related processes, termed the central executive. In the 1974 paper, this central executive possibly had its own memory that crossed domains of representation. By 1986, this general memory had been eliminated from the model, but it was added back again by Baddeley (2000) in the form of an episodic buffer . That seemed necessary to explain short-term memory of features that did not match the other stores (particularly semantic information in memory) and to explain cross-domain associations in working memory, such as the retention of links between names and faces. Because of the work of Baddeley et al. (1975) , working memory is generally viewed as the combination of multiple components working together. Some even include in that bundle the heavy contribution of long-term memory, which reduces the working memory load by organizing and grouping information in working memory into a smaller number of units ( Miller, 1956 ; Ericsson and Kintsch, 1995 ). For example, the letter series IRSCIAFBI can be remembered much more easily as a series of acronyms for three federal agencies of the United States of America: the Internal Revenue Service (IRS), the Central Intelligence Agency (CIA), and the Federal Bureau of Investigation (FBI). However, that factor was not emphasized in the well-known model of Baddeley (1986) .

What is clear from my definition is that working memory includes short-term memory and other processing mechanisms that help to make use of short-term memory. This definition is different from the one used by some other researchers (e.g., Engle, 2002 ), who would like to reserve the term working memory to refer only to the attention-related aspects of short-term memory. This, however, is not so much a debate about substance, but rather a slightly confusing discrepancy in the usage of terms.

One reason to pursue the term working memory is that measures of working memory have been found to correlate with intellectual aptitudes (and especially fluid intelligence) better than measures of short-term memory and, in fact, possibly better than measures of any other particular psychological process (e.g., Daneman and Carpenter, 1980 ; Kyllonen and Christal, 1990 ; Daneman and Merikle, 1996 ; Engle et al., 1999 ; Conway et al., 2005 ). It has been thought that this reflects the use of measures that incorporate not only storage but also processing, the notion being that both storage and processing have to be engaged concurrently to assess working memory capacity in a way that is related to cognitive aptitude. More recently, Engle et al. (1999) introduced the notion that aptitudes and working memory both depend on the ability to control attention, or to apply the control of attention to the management of both primary and secondary memory ( Unsworth and Engle, 2007 ). However, more research is needed on exactly what we learn from the high correlation between working memory and intellectual aptitudes, and this issue will be discussed further after the more basic issue of the short-term versus the long-term memory distinction is addressed.

Meanwhile, it may be helpful to summarize a theoretical framework ( Cowan, 1988 , 1995 , 1999 , 2001 , 2005 ) based on past research. This framework, illustrated in Fig. 1 , helps to account for the relation between long-term, short-term, and working memory mechanisms and explains what I see as the relation between them. In this framework, short-term memory is derived from a temporarily activated subset of information in long-term memory. This activated subset may decay as a function of time unless it is refreshed, although the evidence for decay is still tentative at best. A subset of the activated information is the focus of attention, which appears to be limited in chunk capacity (how many separate items can be included at once). New associations between activated elements can form the focus of attention. Now the evidence related to this modeling framework will be discussed.

The short-term memory/long-term memory distinction

If there is a difference between short- and long-term memory stores, there are two possible ways in which these stores may differ: in duration , and in capacity . A duration difference means that items in short-term storage decay from this sort of storage as a function of time. A capacity difference means that there is a limit in how many items short-term storage can hold. If there is only a limit in capacity, a number of items smaller than the capacity limit could remain in short-term storage until they are replaced by other items. Both types of limit are controversial. Therefore, in order to assess the usefulness of the short-term storage concept, duration and capacity limits will be assessed in turn.

Duration limits

The concept of short-term memory limited by decay over time was present even at the beginning of cognitive psychology, for example in the work of Broadbent (1958) . If decay were the only principle affecting performance in an immediate memory experiment, it would perhaps be easy to detect this decay. However, even in Broadbent’s work contaminating variables were recognized. To assess decay one must take into account, or overcome, contaminating effects of rehearsal, long-term retrieval, and temporal distinctiveness, which will be discussed one at a time in conjunction with evidence for and against decay.

Overcoming contamination from rehearsal

According to various researchers there is a process whereby one imagines how the words on the list are pronounced without saying them aloud, a process called covert verbal rehearsal. With practice, this process comes to occur with a minimum of attention. Guttentag (1984) used a secondary task to show that rehearsal of a list to be recalled was effortful in young children, but not in adults. If, in a particular experimental procedure, no loss of short-term memory is observed, one can attribute that response pattern to rehearsal. Therefore, steps have been taken to eliminate rehearsal through a process termed articulatory suppression, in which a simple utterance such as the word “ the” is repeatedly pronounced by the participant during part or all of the short-term memory task (e.g., Baddeley et al., 1975 ). There is still the possible objection that whatever utterance is used to suppress rehearsal unfortunately causes interference, which could be the true reason for memory loss over time instead of decay.

That problem of interference would appear moot in light of the findings of Lewandowsky et al. (2004) . They presented lists of letters to be recalled and varied how long the participant was supposed to take to recall each item in the list. In some conditions, they added articulatory suppression to prevent rehearsal. Despite that suppression, they observed no difference in performance with the time between items in the response varying between 400 and 1600 ms (or between conditions in which the word “super” was pronounced one, two, or three times between consecutive items in the response). They found no evidence of memory decay.

A limitation of this finding, though, is that covert verbal rehearsal may not be the only type of rehearsal that participants can use. Perhaps there are types that are not prevented by articulatory suppression. In particular, Cowan (1992) suggested that the process of mentally attending to words or searching through the list, an attention-demanding process, could serve to reactivate items to be recalled in a manner similar to covert verbal rehearsal. The key difference is that it would not be expected that articulatory suppression would prevent that type of rehearsal. Instead, to prevent that type of rehearsal an attention-demanding task would have to be used.

Barrouillet et al. (2004 , 2007 ) have results that do seem to suggest that there is another, more attention-demanding type of rehearsal. They have interposed materials between items to be recalled that require choices; they can be numbers to read aloud or multi-choice reaction times. It is found that these interfere with retention to an extent commensurate to the proportion of the inter-item interval used up attending to the distracting items. As the rate of the distracting items goes up, fewer of the to-be-recalled items are recalled. The notion is that when the distracting task does not require attention, the freed-up attention allows an attention- based rehearsal of the items to be recalled. When the interposed task is more automatic and does not require as much attention (e.g., an articulatory suppression task) there is much less effect of the rate of these interposed items.

Based on this logic, one could imagine a version of Lewandowsky’s task in which not articulatory suppression but attention-demanding verbal stimuli are placed between items in the response, and in which the duration of this filled time between items in the response varies from trial to trial. The verbal, attention-demanding stimuli should prevent both attention-based rehearsal and articulation-based rehearsal. If there is decay, then performance should decline across serial positions more severely when longer filled intervals are placed between items in the response. Unfortunately, though, such results might be accounted for alternatively as the result of interference from the distracting stimuli, without the need to invoke decay.

What seems to be needed, then, is a procedure to prevent both articulation-based and attention-based rehearsal without introducing interference. Cowan and Aubuchon (in press) tried out one type of procedure that may accomplish this. They presented lists of seven printed digits in which the time between items varied within a list. In addition to some randomly timed filler lists, there were four critical trial types, in which the six inter-digit blank intervals were all short (0.5 s following each item) or all long (2 s following each item), or comprised three short and then three long intervals, or three long and then three short intervals. Moreover, there were two post-list response cues. According to one cue, the participant was to recall the list with the items in the presented order, but at any rate they wished. According to the other response cue, the list was to be recalled using the same timing in which it was presented. The expectation was that the need to remember the timing in the latter response condition would prevent rehearsal of either type. As a consequence, performance should be impaired on trials in which the first three response intervals are long because, on these trials, there is more time for forgetting of most of the list items. Just as predicted, there was a significant interaction between the response cue and the length of the first half of the response intervals. When participants were free to recall items at their own pace, performance was no better with a short first half ( M =.71) than with a long first half ( M =.74). The slight benefit of a long first half in that situation could occur because it allowed the list to be rehearsed early on in the response. In contrast, when the timing of recall had to match the timing of the list presentation, performance was better with a short first half ( M = .70) than with a long first half ( M = .67). This, then, suggests there could be decay in short-term memory.

Overcoming contamination from long-term retrieval

If there is more than one type of memory storage then there still is the problem of which store provided the information underlying a response. There is no guarantee that, just because a procedure is considered a test of short-term storage, the long-term store will not be used. For example, in a simple digit span task, a series of digits is presented and is to be repeated immediately afterward from memory. If that series turned out to be only slightly different from the participant’s telephone number, the participant might be able to memorize the new number quickly and repeat it from long-term memory. The dual-store theories of memory allow this. Although Broadbent (1958) and Atkinson and Shiffrin (1968) drew their models of information processing as a series of boxes representing different memory stores, with long-term memory following short-term memory, these boxes do not imply that memory is exclusively in one box or another; they are better interpreted as the relative times of the first entry of information from a stimulus into one store and then the next. The question remains, then as to how one can determine if a response comes from short-term memory.

Waugh and Norman (1965) developed a mathematical model to accomplish this. The model operated with the assumption that long-term memory occurs for the entire list, including a plateau in the middle of the list. In contrast, by the time of recall, short-term memory is said to remain only at the end of the list. This model assumes that, for any particular serial position within a list, the likelihood of successful short-term storage (S) and long-term storage (L) are independent, so that the likelihood of recalling the item is S+L−SL.

A slightly different assumption is that short- and long-term stores are not independent but are used in a complementary fashion. The availability of short-term memory of an item may allow resources needed for long-term memorization to be shifted to elsewhere in the list. The data seem more consistent with that assumption. In several studies, lists to be recalled have been presented to patients with Korsakoff’s amnesia and normal control participants ( Baddeley and Warrington, 1970 ; Carlesimo et al., 1995 ). These studies show that, in immediate recall, performance in amnesic individuals is preserved at the last few serial positions of the list. It is as if the performance in those serial positions is based mostly or entirely on short-term storage, and that there is no decrease in that kind of storage in the amnesic patients. In delayed recall, the amnesic patients show a deficit at all serial positions, as one would expect if short-term memory for the end of the list is lost as a function of a filled delay period ( Glanzer and Cunitz, 1966 ).

Overcoming contamination from temporal distinctiveness

Last, it has been argued that the loss of memory over time is not necessarily the result of decay. Instead, it can be caused by temporal distinctiveness in retrieval. This kind of theory assumes that the temporal context of an item serves as a retrieval cue for that item, even in free recall. An item separated in time from all other items is relatively distinctive and easy to recall, whereas an item that is relatively close to other items is more difficult to recall because it shares their temporal cues to retrieval. Shortly after a list is presented the most recent items are the most distinct temporally (much like the distinctness of a telephone pole you are practically touching compared to poles extending further down the road). Across a retention interval, the relative distinctiveness of the most recent items decreases (much like standing far away from even the last pole in a series).

Although there are data that can be interpreted according to distinctiveness, there also are what look like dissociations between the effects of distinctiveness and a genuine short-term memory effect. One can see this, for example, in the classic procedure of Peterson and Peterson (1959) in which letter trigrams are to be recalled immediately or only after a distracting task, counting backward from a starting number by three, for a period lasting up to 18 s. Peterson and Peterson found severe memory loss for the letter trigram as the filled delay was increased. However, subsequently, sceptics argued that the memory loss occurred because the temporal distinctiveness of the current letter trigram diminished as the filled delay increased. In particular, this delay effect was said to occur because of the increase across test delays in the proactive interference from previous trials. On the first few trials, the delay does not matter ( Keppel and Underwood, 1962 ) and no detrimental effect of delay is observed if delays of 5, 10, 15, and 20 s are tested in separate trial blocks ( Turvey et al., 1970 ; Greene, 1996 ).

Yet, there may be a true decay effect at shorter test intervals. Baddeley and Scott (1971) set up a trailer in a shopping mall so that they could test a large number of participants for one trial each, so as to avoid proactive interference. They found an effect of the test delay within the first 5 s but not at longer delays. Still, it seems that the concept of decay is not yet on very firm ground and warrants further study. It may be that decay actually reflects not a gradual degradation of the quality of the short-term memory trace, but a sudden collapse at a point that varies from trial to trial. With a control for temporal distinctiveness, Cowan et al. (1997a) found what could be a sudden collapse in the representation of memory for a tone with delays of between 5 and 10 s.

Chunk capacity limits

The concept of capacity limits was raised several times in the history of cognitive psychology. Miller (1956) famously discussed the “magical number seven plus or minus two” as a constant in short-term processing, including list recall, absolute judgment, and numerical estimation experiments. However, his autobiographical essay ( Miller, 1989 ) indicates that he was never very serious about the number seven; it was a rhetorical device that he used to tie together the otherwise unrelated strands of his research for a talk. Although it is true that memory span is approximately seven items in adults, there is no guarantee that each item is a separate entity. Perhaps the most important point of Miller’s (1956) article was that multiple items can be combined into a larger, meaningful unit. Later studies suggested that the limit in capacity is more typically only three or four units ( Broadbent, 1975 ; Cowan, 2001 ). That conclusion was based on an attempt to take into account strategies that often increase the efficiency of use of a limited capacity, or that allow the maintenance of additional information separate from that limited capacity. To understand these methods of discussing capacity limits I will again mention three types of contamination. These come from chunking and the use of long-term memory, from rehearsal, and from non-capacity-limited types of storage.

Overcoming contamination from chunking and the use of long-term memory

A participant’s response in an immediate-memory task depends on how the information to be recalled is grouped to form multi-item chunks ( Miller, 1956 ). Because it is not usually clear what chunks have been used in recall, it is not clear how many chunks can be retained and whether the number is truly fixed. Broadbent (1975) proposed some situations in which multi-item chunk formation was not a factor, and suggested on the basis of results from such procedures that the true capacity limit is three items (each serving as a single-item chunk). For example, although memory span is often about seven items, errors are made with seven-item lists and the error-free limit is typically three items. When people must recall items from a category in long-term memory, such as the states of the United States, they do so in spurts of about three items on average. It is as if the bucket of short-term memory is filled from the well of long-term memory and must be emptied before it is refilled. Cowan (2001) noted other such situations in which multi-item chunks cannot be formed. For example, in running memory span, a long list of items is presented with an unpredictable endpoint, making grouping impossible. When the list ends, the participant is to recall a certain number of items from the end of the list. Typically, people can recall three or four items from the end of the list, although the exact number depends on task demands ( Bunting et al., 2006 ). Individuals differ in capacity, which ranges from about two to six items in adults (and fewer in children), and the individual capacity limit is a strong correlate of cognitive aptitude.

Another way to take into account the role of multi-item chunk formation is to set up the task in a manner that allows chunks to be observed. Tulving and Patkau (1962) studied free recall of word lists with various levels of structure, ranging from random words to well-formed English sentences, with several different levels of coherence in between. A chunk was defined as a series of words reproduced by the participant in the same order in which the words had been presented. It was estimated that, in all conditions, participants recalled an average of four to six chunks. Cowan et al. (2004) tried to refine that method by testing serial recall of eight-word lists, which were composed of four pairs of words that previously had been associated with various levels of learning (0, 1, 2, or 4 prior word–word pairings). Each word used in the list was presented an equal number of times (four, except in a non-studied control condition) but what varied was how many of those presentations were as singletons and how many were as a consistent pairing. The number of paired prior exposures was held constant across the four pairs in a list. A mathematical model was used to estimate the proportion of recalled pairs that could be attributed to the learned association (i.e., to a two-word chunk) as opposed to separate recall of the two words in a pair. This model suggested that the capacity limit was about 3.5 chunks in every learning condition, but that the ratio of two-word chunks to one-word chunks increased as a function of the number of prior exposures to the pairs in the list.

The issue of rehearsal is not entirely separate from the issue of chunk formation. In the traditional concept of rehearsal (e.g., Baddeley, 1986 ), one imagines that the items are covertly articulated in the presented order at an even pace. However, another possibility is that rehearsal involves the use of articulatory processes in order to put the items into groups. In fact, Cowan et al. (2006a) asked participants in a digit span experiment how they carried out the task and by far the most common answer among adults was that they grouped the items; participants rarely mentioned saying the items to themselves. Yet, it is clear that suppressing rehearsal affects performance.

Presumably, the situations in which items cannot be rehearsed are for the most part the same as the situations in which items cannot be grouped. For example, Cowan et al. (2005) relied on a running memory span procedure in which the items were presented at the rapid rate of 4 per second. At that rate, it is impossible to rehearse the items as they are presented. Instead, the task is probably accomplished by retaining a passive store (sensory or phonological memory) and then transferring the last few items from that store into a more attention-related store at the time of recall. In fact, with a fast presentation rate in running span, instructions to rehearse the items is detrimental, not helpful, to performance ( Hockey, 1973 ). Another example is memory for lists that were ignored at the time of their presentation ( Cowan et al., 1999 ). In these cases, the capacity limit is close to the three or four items suggested by Broadbent (1975) and Cowan (2001) .

It is still quite possible that there is a speech-based short-term storage mechanism that is by and large independent of the chunk-based mechanism. In terms of the popular model of Baddeley (2000) , the former is the phonological loop and the latter, the episodic buffer. In terms of Cowan (1988 , 1995 , 1999 , 2005) , the former is part of activated memory, which may have a time limit due to decay, and the latter is the focus of attention, which is assumed to have a chunk capacity limit.

Chen and Cowan (2005) showed that the time limit and chunk capacity limit in short-term memory are separate. They repeated the procedure of Cowan et al. (2004) in which pairs of words sometimes were presented in a training session preceding the list recall test. They combined lists composed of pairs as in that study. Now, however, both free and serial recall tasks were used, and the length of list varied. For long lists and free recall, the chunk capacity limit governed the recall. For example, lists of six well-learned pairs were recalled as well as lists of six unpaired singletons (i.e., were recalled at similar proportions of words correct). For shorter lists and serial recall strictly scored, the time limit instead governed the recall. For example, lists of four well-learned pairs were not recalled nearly as well as lists of four unpaired singletons, but only as well as lists of eight unpaired singletons. For intermediate conditions it appeared as if chunk capacity limits and time limits operate together to govern recall. Perhaps the capacity-limited mechanism holds items and the rehearsal mechanism preserves some serial order memory for those held items. The exact way in which these limits work together is not yet clear.

Overcoming contamination from non-capacity-limited types of storage

It is difficult to demonstrate a true capacity limit that is related to attention if, as I believe, there are other types of short-term memory mechanisms that complicate the results. A general capacity should include chunks of information of all sorts: for example, information derived from both acoustic and visual stimuli, and from both verbal and nonverbal stimuli. If this is the case, there should be cross-interference between one type of memory load and another. However, the literature often has shown that there is much more interference between similar types of memoranda, such as two visual arrays of objects or two acoustically presented word lists, than there is between two dissimilar types, such as one visual array and one verbal list. Cocchini et al. (2002) suggested that there is little or no interference between dissimilar lists. If so, that would appear to provide an argument against the presence of a general, cross-domain, short-term memory store.

Morey and Cowan (2004 , 2005) questioned this conclusion. They presented a visual array of colored spots to be compared to a second array that matched the first or differed from it in one spot’s color. Before the first array or just after it, participants sometimes heard a list of digits that was then to be recited between the two arrays. In a low-load condition, the list was their own seven-digit telephone number whereas, in a high-load condition, it was a random seven-digit number. Only the latter condition interfered with array-comparison performance, and then only if the list was to be recited aloud between the arrays. This suggests that retrieving seven random digits in a way that also engages rehearsal processes relies upon some type of short-term memory mechanism that also is needed for the visual arrays. That shared mechanism may be the focus of attention, with its capacity limit. Apparently, though, if the list was maintained silently rather than being recited aloud, this silent maintenance occurred without much use of the common, attention-based storage mechanism, so visual array performance was not much affected.

The types of short-term memory whose contribution to recall may obscure the capacity limit can include any types of activated memory that fall outside of the focus of attention. In the modeling framework depicted in Fig. 1 , this can include sensory memory features as well as semantic features. Sperling (1960) famously illustrated the difference between unlimited sensory memory and capacity-limited categorical memory. If an array of characters was followed by a partial report cue shortly after the array, most of the characters in the cued row could be recalled. If the cue was delayed about 1 s, most of the sensory information had decayed and performance was limited to about four characters, regardless of the size of the array. Based on this study, the four-character limit could be seen as either a limit in the capacity of short-term memory or a limit in the rate with which information could be transferred from sensory memory into a categorical form before it decayed. However, Darwin et al. (1972) carried out an analogous auditory experiment and found a limit of about four items even though the observed decay period for sensory memory was about 4s. Given the striking differences between Sperling and Darwin et al. in the time period available for the transfer of information to a categorical form, the common four-item limit is best viewed as a capacity limit rather than a rate limit.

Saults and Cowan (2007) tested this conceptual framework in a series of experiments in which arrays were presented in two modalities at once or, in another procedure, one after the other. A visual array of colored spots was supplemented by an array of spoken digits occurring in four separate loudspeakers, each one consistently assigned to a different voice to ease perception. On some trials, participants knew that they were responsible for both modalities at once whereas, in other trials, participants knew that they were responsible for only the visual or only the acoustic stimuli. They received a probe array that was the same as the previous array (or the same as one modality in that previous array) or differed from the previous array in the identity of one stimulus. The task was to determine if there was a change. The use of cross-modality, capacity-limited storage predicts a particular pattern of results. It predicts that performance on either modality should be diminished in the dual-modality condition compared to the unimodal conditions, due to strain on the cross-modality store. That is how the results turned out. Moreover, if the cross-modality, capacity-limited store were the only type of storage used, then the sum of visual and auditory capacities in the dual-modality condition should be no greater than the larger of the two unimodal capacities (which happened to be the visual capacity). The reason is that the limited-capacity store would hold the same number of units no matter whether they were all from one modality or were from two modalities combined. That prediction was confirmed, but only if there was a post-perceptual mask in both modalities at once following the array to be remembered. The post-perceptual mask included a multicolored spot at each visual object location and a sound composed of all possible digits overlaid, from each loudspeaker. It was presented long enough after the arrays to be recalled that their perception would have been complete (e.g., 1 s afterward; cf. Vogel et al., 2006 ). Presumably, the mask was capable of overwriting various types of sensory-specific features in activated memory, leaving behind only the more generic, categorical information present in the focus of attention, which presumably is protected from masking interference by the attention process. The limit of the focus of attention was again shown to be between three and four items, for either unimodal visual or bimodal stimuli.

Even without using masking stimuli, it may be possible to find a phase of the short-term memory process that is general across domains. Cowan and Morey (2007) presented two stimulus sets to be recalled (or, in control conditions, only one set). The two stimulus sets could include two spoken lists of digits, two spatial arrays of colored spots, or one of each, in either order. Following this presentation, a cue indicated that the participant would be responsible for only the first array, only the second array, or both arrays. Three seconds followed before a probe. The effect of memory load could be compared in two ways. Performance on those trials in which two sets of stimuli were presented and both were cued for retention could be compared either to trials in which only one set was presented, or it could be compared to trials in which both sets were presented but the cue later indicated that only one set had to be retained. The part of working memory preceding the cue showed modality-specific dual-task effects: encoding a stimulus set of one type was hurt more by also encoding another set if both sets were in the same modality. However, the retention of information following the cue showed dual-task effects that were not modality-specific. When two sets had been presented, retaining both of them was detrimental compared to retaining only one set (as specified by the post-stimulus retention cue to retain one versus both sets), and this dual-task effect was similar in magnitude no matter whether the sets were in the same or different modalities. After the initial encoding, working memory storage across several seconds thus may occur abstractly, in the focus of attention.

Other evidence for a separate short-term storage

Last, there is other evidence that does not directly support either temporal decay or a capacity limit specifically, but implies that one or the other of these limits exist. Bjork and Whitten (1974) and Tzeng (1973) made temporal distinctiveness arguments on the basis of what is called continual distractor list recall, in which a recency effect persists even when the list is followed by a distracter-filled delay before recall. The filled delay should have destroyed short-term memory but the recency effect occurs anyway, provided that the items in the list also are separated by distracter-filled delays to increase their distinctiveness from one another. In favor of short-term storage, though, other studies have shown dissociations between what is found in ordinary immediate recall versus continual distractor recall (e.g., word length effects reversed in continual distractor recall: Cowan et al., 1997b ; proactive interference at the most recent list positions in continual distractor recall only: Craik & Birtwistle, 1971 ; Davelaar et al., 2005 ).

There is also additional neuroimaging evidence for short-term storage. Talmi et al. (2005) found that recognition of earlier portions of a list, but not the last few items, activated areas within the hippocampal system that is generally associated with long-term memory retrieval. This is consistent with the finding, mentioned earlier, that memory for the last few list items is spared in Korsakoff’s amnesia ( Baddeley and Warrington, 1970 ; Carlesimo et al., 1995 ). In these studies, the part of the recency effect based on short-term memory could reflect a short amount of time between presentation and recall of the last few items, or it could reflect the absence of interference between presentation and recall of the last few items. Thus, we can say that short-term memory exists, but often without great clarity as to whether the limit is a time limit or a chunk capacity limit.

The short-term memory/working memory distinction

The distinction between short-term memory and working memory is clouded in a bit of confusion but that is largely the result of different investigators using different definitions. Miller et al. (1960) used the term “working memory” to refer to temporary memory from a functional standpoint, so from their point of view there is no clear distinction between short-term and working memory. Baddeley and Hitch (1974) were fairly consistent with this definition but overlaid some descriptions on the terms that distinguished them. They thought of short-term memory as the unitary holding place as described by, for example, Atkinson and Shiffrin (1968) . When they realized that the evidence actually was consistent with a multi-component system that could not be reduced to a unitary short-term store, they used the term working memory to describe that entire system. Cowan (1988) maintained a multi-component view, like Baddeley and Hitch, but without a commitment to precisely their components; instead, the basic subdivisions of working memory were said to be the short-term storage components (activated memory along with the focus of attention within it, shown in Fig. 1 ) and central executive processes that manipulate stored information. By Cowan’s account, Baddeley’s (1986) phonological loop and visuospatial sketchpad would be viewed as just two of many aspects of activated memory, which are susceptible to interference to a degree that depends upon the similarity between features of the activated and interfering information sources. Baddeley’s (2000) episodic buffer is possibly the same as the information saved in Cowan’s focus of attention, or at least is a closely similar concept.

There has been some shift in the definition or description of working memory along with a shift in the explanation of why the newer working memory tasks correlate with intelligence and aptitude measures so much more highly than do simple, traditional, short-term memory tasks such as serial recall. Daneman and Carpenter (1980) had assumed that what is critical is to use working memory tasks that include both storage and processing components, so as to engage all of the parts of working memory as described, for example, by Baddeley and Hitch (1974) . Instead, Engle et al. (1999) and Kane et al. (2001) proposed that what is critical is whether the working memory task is challenging in terms of the control of attention. For example, Kane et al. found that working memory span storage-and-processing tasks correlates well with the ability to inhibit the natural tendency to look toward a suddenly appearing stimulus and instead to look the other way, the antisaccade task. Similarly, Conway et al. (2001) found that individuals scoring high on storage-and-processing tests of working memory notice their names in a channel to be ignored in dichotic listening much less often than low-span individuals; the high-span individuals apparently are better able to make their primary task performance less vulnerable to distraction, but this comes at the expense of being a bit oblivious to irrelevant aspects of their surroundings. In response to such research, Engle and colleagues sometimes used the term working memory to refer only to the processes related to controlling attention. By doing so, their definition of working memory seems at odds with previous definitions but that new definition allows the simple statement that working memory correlates highly with aptitudes, whereas short-term memory (redefined to include only the non-attention-related aspects of memory storage) does not correlate so highly with aptitudes.

Cowan et al. (2006b) , while adhering to the more traditional definition of working memory, made an assertion about working memory similar to that of Engle and colleagues, but a bit more complex. They proposed, on the basis of some developmental and correlational evidence, that multiple functions of attention are relevant to individual differences in aptitudes. The control of attention is relevant, but there is an independent contribution from the number of items that can be held in attention, or its scope. According to this view, what may be necessary for a working memory procedure to correlate well with cognitive aptitudes is that the task must prevent covert verbal rehearsal so that the participant must rely on more attention-demanding processing and/or storage to carry out the task. Cowan et al. (2005) found that the task can be much simpler than the storage-and-processing procedures. For example, in a version of the running memory span test, digits are presented very quickly and the series stops at an unpredictable point, after which the participant is to recall as many items as possible from the end of the list. Rehearsal is impossible and, when the list ends, information presumably must be retrieved from activated sensory or phonological features into the focus of attention. This type of task correlated with aptitudes, as did several other measures of the scope of attention ( Cowan et al., 2005 , 2006b ). In children too young to use covert verbal rehearsal (unlike older children and adults), even a simple digit span task served as an excellent correlate with aptitudes.

Other research verifies this idea that a working memory test will correlate well with cognitive aptitudes to the extent that it requires that attention be used for storage and/or processing. Gavens and Barrouillet (2004) carried out a developmental study in which they controlled the difficulty and duration of a processing task that came between items to be recalled. There still was a developmental difference in span, which they attributed to the development of a basic capacity, which could reflect a developmental increase in the scope of attention (cf. Cowan et al., 2005 ). Lépine et al. (2005) showed that what was important for a storage-and-processing type of span task to correlate well with aptitudes is for the processing component of the task (in this case, reading letters aloud) to occur quickly enough to prevent various types of rehearsal to sneak in between (see also Conlin et al., 2005 ).

Several papers have pitted storage and processing (perhaps the scope versus control of attention?) against one another to see which is more important in accounting for individual differences. Vogel et al. (2005) used a visual array task modified for use with a component of event-related potentials that indicates storage in visual working memory, termed contralateral delay activity (CDA). This activity was found to depend not only on the number of relevant objects in the display (e.g., red bars at varying angles to be remembered), but sometimes also on the number of irrelevant objects to be ignored (e.g., blue bars). For high-span individuals, the CDA for two relevant objects was found to be similar whether or not there also were two irrelevant objects in the display. However, for low-span individuals, the CDA for two relevant objects combined with two irrelevant objects was similar to the CDA for displays with four relevant objects alone, as if the irrelevant objects could not be excluded from working memory. One limitation of the study is that the separation of participants into high versus low span was based on the CDA also, and the task used to measure the CDA inevitably required selective attention (to one half of the display) on every trial, whether or not it included objects of an irrelevant color.

Gold et al. (2006) investigated similar issues in a behavioral design, and testing the difference between schizophrenic patients and normal control participants. Each trial started with a cue to attend to one part of the display at the expense of another (e.g., bars of one relevant color but not another, irrelevant color). The probe display was a set that was cued for relevance on most trials (in some experiments, 75%) whereas, occasionally, the probe display was a set that was not cued. This allowed a separate measure of the control of attention (the advantage for cued items over uncued items) and the storage capacity of working memory (the mean number of items recalled from each array, adding across cued and uncued sets). Unlike the initial expectations, the clear result was that the difference between groups was in the capacity, not in the control of attention. It would be interesting to know whether the same type of result could be obtained for high versus low span normal individuals, or whether that comparison instead would show a control-of-attention difference between these groups as Vogel et al. (2005) must predict. Friedman et al. (2006) found that not all central executive functions correlated with aptitudes; updating working memory did, but inhibition and shifting of attention did not. On the other hand, recall that Cowan et al. (2006b) did find was that a control-of-attention task was related to aptitudes.

In sum, the question of whether short-term memory and working memory are different may be a matter of semantics. There are clearly differences between simple serial recall tasks that do not correlate very well with aptitude tests in adults, and other tasks requiring memory and processing, or memory without the possibility of rehearsal, that correlate much better with aptitudes. Whether to use the term working memory for the latter set of tasks, or whether to reserve that term for the entire system of short-term memory preservation and manipulation, is a matter of taste. The more important, substantive question may be why some tasks correlate with aptitude much better than others.

The distinction between long-term and short-term memory depends on whether it can be demonstrated that there are properties specific to short-term memory; the main candidates include temporal decay and a chunk capacity limit. The question of decay is still pretty much open to debate, whereas there is growing support for a chunk capacity limit. These limits were discussed in a framework shown in Fig. 1 .

The distinction between short-term memory and working memory is one that depends on the definition that one accepts. Nevertheless, the substantive question is why some tests of memory over the short term serve as some of the best correlates of cognitive aptitudes, whereas others do not. The answer seems to point to the importance of an attentional system used both for processing and for storage. The efficiency of this system and its use in working memory seem to differ substantially across individuals (e.g., Conway et al., 2002 ; Kane et al., 2004 ; Cowan et al., 2005 , 2006b ), as well as improving with development in childhood ( Cowan et al., 2005 , 2006b ) and declining in old age ( Naveh-Benjamin et al., 2007 ; Stoltzfus et al., 1996 ; Cowan et al., 2006c ).

Acknowledgment

This work was completed with the assistance of NIH Grant R01 HD-21338.

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Science project, short term memory.

Grade Level: 5th - 8th; Type: Psychology

To test the efficiency of short term memory.

The purpose of this experiment is to determine how many things a person can hold in their short term or active memory at once.

Research Questions

• What is the difference between short term and long term memory?
• Are short term and long term memories stored in different places in the brain?
• What is the role of the working memory?
• What tools do people use to increase the capacity and duration of the short term memory?
• How do people use chunking to increase the efficiency of the short term memory?

The process of transferring information from the short term to the long term memory is a complicated one. Often, this transfer takes multiple attempts and requires a significant amount of concentration and attention. Though many students studying for a test will devote considerable time and energy to memorizing new information, some students choose to “cram” for a test at the last minute. While this make help in rare cases, the majority of people cannot transfer information from their short term memory to their long term memory quickly. Furthermore, most people can only hold between five and nine bits of information in their short term memory, which leaves room for only a few key terms or equations right before the test. Studying the efficiency of short term memory can help us learn what the limitations of this form of memory are and also how to overcome those limitations.

• 20 or more subjects
• Displays with 20 numbers, letters, or objects printed on them

Experimental Procedure :

• Find a number of people willing to participate in your study.
• Have your subjects sit down in desks.
• Have your subjects record their age, gender and any other information you wish to collect on their paper. It is not necessary to collect the names of your subjects.
• Explain the process of the study to your subjects. Tell them that they will be shown a series of numbers, letters and pictures and that they are to list as many of these as they can. Tell them not to make guesses, but to only list the things they remember.
• Display a list of numbers, such as the one below. You can use an overhead projector, an Elmo or even a piece of poster board.
• Leave the numbers up for 10 seconds.
• Have your subjects record as many as they can remember.
• Give your subjects a one minute break to clear their memories.
• Display a list of letters, such as the one below. You can use an overhead projector, an Elmo or even a piece of poster board.
• Leave the letters up for 10 seconds.
• Display a series of simple pictures of common objects. Clip art is acceptable. You can use an overhead projector, an Elmo or even a piece of poster board.
• Leave the pictures up for 10 seconds.
• Have your subjects record as many as they can remember. They can use a word or two to describe the pictures they remember.
• Collect the papers from your subjects and compare the results.

7   19   86    3   55   17   43   26   97   11   2   74   56   93   12   84   33   1   19   52  

P   L   F    E   T   U   B   W   M   X   Z   Q   K   O   S   R   C   N   B   D  

Terms/Concepts: Short term memory; Long term memory; Active memory; Working memory; Phonological loop; Visuospacial sketchpad; Visual short term memory; Memory span; Chunking

References:

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How Short-Term Memory Works

• Transfer to Long-Term Memory
• Short-Term Memory Loss

Frequently Asked Questions

Short-term memory is the capacity to store a small amount of information in the mind and keep it readily available for a short period of time. It is also known as primary or active memory.

Short-term memory is essential for daily functioning, which is why experiencing short-term memory loss can be frustrating and even debilitating.

• Short-term memory is very brief . When short-term memories are not rehearsed or actively maintained, they last mere seconds.
• Short-term memory is limited . It is commonly suggested that short-term memory can hold only seven items at once, plus or minus two.

How Long Is Short-Term Memory For?

Most of the information kept in short-term memory will be stored for approximately 20 to 30 seconds, or even less. Some information can last in short-term memory for up to a minute, but most information spontaneously decays quite quickly, unless you use rehearsal strategies such as saying the information aloud or mentally repeating it.

However, the information in short-term memory is also highly susceptible to interference . Any new information that enters short-term memory will quickly displace old information . Similar items in the environment can also interfere with short-term memories.

For example, you might have a harder time remembering someone's name if you're in a crowded, noisy room, or if you were thinking of what to say to the person rather than paying attention to their name.

While many short-term memories are quickly forgotten, attending to this information allows it to continue the next stage — long-term memory .

The amount of information that can be stored in short-term memory can vary. In 1956, in an influential paper titled "The Magical Number Seven, Plus or Minus Two," psychologist George Miller suggested that people can store between five and nine items in short-term memory.

More recent research suggests that people are capable of storing approximately four chunks or pieces of information in short-term memory.

For example, imagine that you are trying to remember a phone number. The other person rattles off the 10-digit phone number, and you make a quick mental note. Moments later you realize that you have already forgotten the number. Without rehearsing or continuing to repeat the number until it is committed to memory, the information is quickly lost from short-term memory.

Short-Term vs. Working Memory

Some researchers argue that working memory and short-term memory significantly overlap, and may even be the same thing. The distinction is that working memory refers to the ability to use, manipulate, and apply memory for a period of time (for example, recalling a set of instructions as you complete a task), while short-term memory refers only to the temporary storage of information in memory.

The Baddeley-Hitch model of working memory suggests that there are two components of working memory: a place where you store visual and spatial information (visuospatial scratchpad), and a place where you record auditory information (phonological loop). In addition, the model suggests there is a "central executive" that controls and mediates these two components as well as processes information, directs attention , sets goals, and makes decisions .

How Short-Term Memory Becomes Long-Term Memory

Memory researchers often use what is referred to as the three-store model to conceptualize human memory. This model suggests that memory consists of three basic stores— sensory , short-term, and long-term—and that each of these can be distinguished based on storage capacity and duration.

While long-term memory has a seemingly unlimited capacity that lasts years, short-term memory is relatively brief and limited. Short-term memory is limited in both capacity and duration. In order for a memory to be retained, it needs to be transferred from short-term stores into long-term memory. The exact mechanisms for how this happens remain controversial and not well understood.

The classic model, known as the Atkinson-Shiffrin model or multi-modal model, suggested that all short-term memories were automatically placed in long-term memory after a certain amount of time.

More recently, researchers have proposed that some mental editing takes place and that only particular memories are selected for long-term retention. Factors such as time and interference can affect how information in encoded in memory.

The information-processing view of memory suggests that human memory works much like a computer. In this model, information first enters short-term memory (a temporary holding store for recent events) and then some of this information is transferred into long-term memory (a relatively permanent store), much like information on a computer being placed on a hard disk.

Some researchers, however, dispute the idea that there are separate stores for short-term and long-term memories at all.

Maintenance Rehearsal

Maintenance rehearsal (or rehearsal) can help move memories from short-term to long-term memory. For example, you might use this approach when studying materials for an exam. Instead of just reviewing the information once or twice, you might go over your notes repeatedly until the critical information is committed to memory.

Chunking is one memorization technique that can facilitate the transfer of information into long-term memory. This approach involves organizing information into more easily learned groups, phrases, words, or numbers.

For example, it will take a large amount of effort to memorize the following number: 65,495,328,463. However, it will be easier to remember if it is chunked into the following: 6549 532 8463.

Easily remembered mnemonic phrases, abbreviations, or rhymes can help move short-term memories into long-term storage. A few common examples include:

• ROY G BIV : An acronym that represents the first letter of each color of the rainbow—red, orange, yellow, green, blue, indigo, violet
• I before E, except after C : A rhyme used to remember the spelling of common words
• Thirty days hath September... : A poem used to remember how many days are in each month

Another mnemonic strategy, which dates back to around 500 BCE, is the method of loci. The method of loci involves mentally placing the items you are trying to learn or remember around a room—such as on the sofa, next to a plant, or on the window seat. To trigger your memory, you then visualize yourself going to each location, triggering your recall for that information.

Memory Consolidation

Memory consolidation is the process in which the brain converts short-term memories into long-term ones. Rehearsing or recalling information over and over again creates structural changes in the brain that strengthen neural networks. The repeated firing of two neurons makes it more likely that they will repeat that firing again in the future.

What Is Considered Short-Term Memory Loss?

For most of us, it's pretty common to experience an episode of memory loss occasionally. This can look like missing a monthly payment, forgetting the date, losing our keys, or having trouble finding the right word to use from time to time.

If you feel like you're constantly forgetting things, it can be irritating, frustrating, and frightening. Short-term memory loss may even make you worried that your brain is too reliant on devices like your smartphone rather than your memory to recall information.

What Is Short-Term Memory a Symptom of?

Mild memory loss doesn't always indicate a problem, and certain memory changes are a normal part of aging. Short-term memory loss can also be caused by other, non-permanent factors , including:

• Alcohol or drug use
• Medication side effects
• Sleep deprivation

If you are concerned about memory lapses or any other brain changes, talk to your healthcare provider. They can give you a thorough exam to determine what might be causing your symptoms and recommend lifestyle changes, strategies, or treatments to improve your short-term memory .

Short-term memory plays a vital role in shaping our ability to function in the world around us, but it is limited in terms of both capacity and duration. Disease and injury as well as increasing reliance on smartphones can also have an influence on the ability to store short-term memories. As researchers continue to learn more about factors that influence memory, new ways of enhancing and protecting short-term memory may emerge.

There are many potential causes of short-term memory loss, and many of them are reversible. Memory loss may be a side effect of medication (or a combination of medications). It can occur after a head injury or as a result of vitamin B-12 deficiency. Hypothyroidism (an underactive thyroid gland) can affect memory. So can stress, anxiety, depression, and alcohol use. Or, memory loss could be a symptom of a serious condition, such as dementia or a brain tumor.

Maintenance rehearsal is a way to preserve information in long-term memory. It might mean repeating or otherwise accessing information that is stored in long-term memory to make sure that you retain it.

Living a healthy lifestyle may help preserve and improve memory. That means getting regular physical activity, eating a healthy diet, limiting alcohol and drug use, and sleeping well.

It's also important to keep your brain active. Regular social interactions, along with cognitive activities like word games and learning new skills, may help keep memory issues at bay.

You can also use techniques like mnemonics, rehearsal, chunking, and organizational strategies (such as taking notes and using phone alarms) to help support your memory.

Cowan N. What are the differences between long-term, short-term, and working memory? .  Prog Brain Res . 2008;169:323-338. doi:10.1016/S0079-6123(07)00020-9

Miller GA. The magical number seven plus or minus two: Some limits on our capacity for processing information . Psychol Rev . 1956;63(2):81–97.

Atkinson RC, Shiffrin RM. The control processes of short-term memory . Institute for Mathematical Studies in the Social Sciences, Stanford University.

Kelley P, Evans MDR, Kelley J. Making memories: Why time matters .  Front Hum Neurosci . 2018;12:400. doi:10.3389/fnhum.2018.00400

Chai WJ, Abd Hamid AI, Abdullah JM. Working memory from the psychological and neurosciences perspectives: A review .  Front Psychol . 2018;9:401. doi:10.3389/fpsyg.2018.00401

Zlotnik G, Vansintjan A. Memory: An extended definition .  Front Psychol . 2019;10:2523. doi:10.3389/fpsyg.2019.02523

Adams EJ, Nguyen AT, Cowan N. Theories of working memory: Differences in definition, degree of modularity, role of attention, and purpose .  Lang Speech Hear Serv Sch . 2018;49(3):340-355. doi:10.1044/2018_LSHSS-17-0114

Legge ELG, Madan CR, Ng ET, Caplan JB. Building a memory palace in minutes: Equivalent memory performance using virtual versus conventional environments with the Method of Loci . Acta Psychol (Amst) . 2012;141(3):380-390. doi:10.1016/j.actpsy.2012.09.002

National Institute on Aging. Do memory problems always mean Alzheimer's disease? .

Mayo Clinic. Memory loss: When to seek help .

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Memory Stages: Encoding Storage and Retrieval

Saul McLeod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

Learn about our Editorial Process

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

On This Page:

“Memory is the process of maintaining information over time.” (Matlin, 2005) “Memory is the means by which we draw on our past experiences in order to use this information in the present’ (Sternberg, 1999).

Memory is the term given to the structures and processes involved in the storage and subsequent retrieval of information.

Memory is essential to all our lives. Without a memory of the past, we cannot operate in the present or think about the future. We would not be able to remember what we did yesterday, what we have done today, or what we plan to do tomorrow.  Without memory, we could not learn anything.

Memory is involved in processing vast amounts of information. This information takes many different forms, e.g., images, sounds, or meaning.

For psychologists, the term memory covers three important aspects of information processing :

Memory Encoding

When information comes into our memory system (from sensory input), it needs to be changed into a form that the system can cope with so that it can be stored.

Think of this as similar to changing your money into a different currency when you travel from one country to another.  For example, a word that is seen (in a book) may be stored if it is changed (encoded) into a sound or a meaning (i.e., semantic processing).

There are three main ways in which information can be encoded (changed):

1. Visual (picture) 2. Acoustic (sound) 3. Semantic (meaning)

For example, how do you remember a telephone number you have looked up in the phone book?  If you can see it, then you are using visual coding, but if you are repeating it to yourself, you are using acoustic coding (by sound).

Evidence suggests that this is the principle coding system in short-term memory (STM) is acoustic coding.  When a person is presented with a list of numbers and letters, they will try to hold them in STM by rehearsing them (verbally).

Rehearsal is a verbal process regardless of whether the list of items is presented acoustically (someone reads them out), or visually (on a sheet of paper).

The principle encoding system in long-term memory (LTM) appears to be semantic coding (by meaning).  However, information in LTM can also be coded both visually and acoustically.

Memory Storage

This concerns the nature of memory stores, i.e., where the information is stored, how long the memory lasts (duration), how much can be stored at any time (capacity) and what kind of information is held.

The way we store information affects the way we retrieve it.  There has been a significant amount of research regarding the differences between Short Term Memory (STM ) and Long Term Memory (LTM).

Most adults can store between 5 and 9 items in their short-term memory.  Miller (1956) put this idea forward, and he called it the magic number 7.  He thought that short-term memory capacity was 7 (plus or minus 2) items because it only had a certain number of “slots” in which items could be stored.

However, Miller didn’t specify the amount of information that can be held in each slot.  Indeed, if we can “chunk” information together, we can store a lot more information in our short-term memory.  In contrast, the capacity of LTM is thought to be unlimited.

Information can only be stored for a brief duration in STM (0-30 seconds), but LTM can last a lifetime.

Memory Retrieval

This refers to getting information out of storage.  If we can’t remember something, it may be because we are unable to retrieve it.  When we are asked to retrieve something from memory, the differences between STM and LTM become very clear.

STM is stored and retrieved sequentially.  For example, if a group of participants is given a list of words to remember and then asked to recall the fourth word on the list, participants go through the list in the order they heard it in order to retrieve the information.

LTM is stored and retrieved by association.  This is why you can remember what you went upstairs for if you go back to the room where you first thought about it.

Organizing information can help aid retrieval.  You can organize information in sequences (such as alphabetically, by size, or by time).  Imagine a patient being discharged from a hospital whose treatment involved taking various pills at various times, changing their dressing, and doing exercises.

If the doctor gives these instructions in the order that they must be carried out throughout the day (i.e., in the sequence of time), this will help the patient remember them.

Criticisms of Memory Experiments

A large part of the research on memory is based on experiments conducted in laboratories.  Those who take part in the experiments – the participants – are asked to perform tasks such as recalling lists of words and numbers.

Both the setting – the laboratory – and the tasks are a long way from everyday life.  In many cases, the setting is artificial, and the tasks are fairly meaningless.  Does this matter?

Psychologists use the term ecological validity to refer to the extent to which the findings of research studies can be generalized to other settings.  An experiment has high ecological validity if its findings can be generalized, that is, applied or extended to settings outside the laboratory.

It is often assumed that if an experiment is realistic or true-to-life, then there is a greater likelihood that its findings can be generalized.  If it is not realistic (if the laboratory setting and the tasks are artificial) then there is less likelihood that the findings can be generalized.  In this case, the experiment will have low ecological validity.

Many experiments designed to investigate memory have been criticized for having low ecological validity.  First, the laboratory is an artificial situation.  People are removed from their normal social settings and asked to take part in a psychological experiment.

They are directed by an “experimenter” and may be placed in the company of complete strangers.  For many people, this is a brand new experience, far removed from their everyday lives.  Will this setting affect their actions? Will they behave normally?

He was especially interested in the characteristics of people whom he considered to have achieved their potential as individuals.

Often, the tasks participants are asked to perform can appear artificial and meaningless.  Few, if any, people would attempt to memorize and recall a list of unconnected words in their daily lives.  And it is not clear how tasks such as this relate to the use of memory in everyday life.

The artificiality of many experiments has led some researchers to question whether their findings can be generalized to real life.  As a result, many memory experiments have been criticized for having low ecological validity.

Matlin, M. W. (2005). Cognition . Crawfordsville: John Wiley & Sons, Inc.

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.

Sternberg, R. J. (1999). Cognitive psychology (2 nd ed.) . Fort Worth, TX: Harcourt Brace College Publishers.

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Optimizing cnn-lstm for the localization of false data injection attacks in power systems.

1. Introduction

• A deep learning-based method for locating FDIAs in power systems is proposed, utilizing a CNN-LSTM classifier to locate the compromised bus or line.
• The method employs a GA to optimize various hyperparameters of the neural network, thereby achieving a model with superior positioning performance.
• The performance and practicality of the model are demonstrated through extensive experiments, and this method is compared with other advanced FDIA localization methods.

2. Power System State Estimation and False Data Injection Attack

2.1. state estimation and bad data detection, 2.2. false data injection attack, 3. methodology, 3.1. convolutional neural network model, 3.2. long short-term memory model, 3.3. genetic algorithm.

• Population initialization: a random initial population is generated, and individuals within the population are encoded.
• Fitness evaluation: the fitness of each individual is calculated, and individuals with low fitness are eliminated.
• Selection: based on fitness assessment, the individuals with high fitness are selected to participate in the reproduction of the next generation.
• Crossover: the selected individuals are paired according to a set crossover rate, and offspring are produced through crossover operations.
• Mutation: random variations are introduced in the genotype, simulating the process of biological mutation.
• Iteration and termination: the genetic operations are repeated until the termination condition is met, and the individual with the highest fitness is selected as the optimal solution to the problem.

3.4. FDIA Localization Method Based on GA-CNN-LSTM

4. simulation experiments, 4.1. simulation experiment settings, 4.2. evaluation index, 4.3. simulation results, 4.4. comparative experiments and analysis, 4.4.1. robustness comparison, 4.4.2. comparison with other detection methods, 4.4.3. comparison of the detection times, 5. discussion, 6. conclusions, author contributions, institutional review board statement, informed consent statement, data availability statement, acknowledgments, conflicts of interest.

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Share and Cite

Li, Z.; Xie, Y.; Ma, R.; Wei, Z. Optimizing CNN-LSTM for the Localization of False Data Injection Attacks in Power Systems. Appl. Sci. 2024 , 14 , 6865. https://doi.org/10.3390/app14166865

Li Z, Xie Y, Ma R, Wei Z. Optimizing CNN-LSTM for the Localization of False Data Injection Attacks in Power Systems. Applied Sciences . 2024; 14(16):6865. https://doi.org/10.3390/app14166865

Li, Zhuo, Yaobin Xie, Rongkuan Ma, and Zihan Wei. 2024. "Optimizing CNN-LSTM for the Localization of False Data Injection Attacks in Power Systems" Applied Sciences 14, no. 16: 6865. https://doi.org/10.3390/app14166865

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