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Short-term memory

 
Sci-Tech Dictionary: short-term memory
 
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(′shört ′tərm ′mem·rē)

(psychology) Conscious, brief retention of information that is currently being processed in a person's mind.

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Dental Dictionary: short-term memory
 
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The ability to retain and recall recent events or experiences.

 
Sports Science and Medicine: short-term memory
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STM

According to the black-box model of memory, short-term memory is a component of the information-processing system in which new information must remain for a minimum of 20-30 s or the information will be lost. The STM acts as a link between the short-term sensory store (STS) and the long-term memory (LTM). The short-term memory is thought to be analogous to consciousness and has been described as the ‘work space’ where information from the STS and LTM can be brought together for processing.

 
Science Dictionary: short-term memory
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Retention of information that undergoes little processing or interpretation and can be recalled for only a few seconds. Short-term memory can retain about seven items.

  • A popular example of short-term memory is the ability to remember a seven-digit telephone number just long enough to dial a call. In most cases, unless the number is consciously repeated several times, it will be forgotten.

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    World of the Mind: short-term memory
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    Memory for what happened an hour ago or a year ago fulfils an obvious function in our lives. However, our capacity to store information for periods measured in seconds is equally if not more important to our integrity as human beings. This capacity is referred to as short-term memory (STM). Descartes asserted, 'I think, therefore I am'. It is equally true to say 'I think, therefore I have short-term memory'. Indeed any mental activity extended in time, including the production and comprehension of language, must involve STM. It is certainly fortunate that STM is robust and, unlike long-term memory, is seldom affected by old age, drugs, or brain damage.

    The most familiar fact about STM is the existence of the so-called span of immediate memory. A rough definition of the span is that it is the longest sequence of items that can be reproduced correctly following a single presentation. However, the same individual may manage a sequence of seven items on one occasion and make a mistake with a sequence of only five items on another. Accordingly, the span is in fact defined as that length of sequence for which the chance of correct reproduction is 50–50. The span has a number of interesting properties. Two are as follows. First, for items in random order, the span is about seven, plus or minus two. This is surprising in that the amount of information per item has little effect on the span. For example, the span for binary digits (0, 1) is only slightly longer than for decimal digits (the digits 0 to 9), although the latter contains over three times as much information. Second, within wide limits, the span is almost unaffected by the rate at which items are presented, and is therefore relatively independent of the time elapsing between the presentation of an item and its recall. These two facts are nicely explained by the so-called slot theory. On this theory, the span reflects the capacity of an information store in the brain with about seven 'slots'. Each slot is capable of storing a single item or unit. Once the store is full, new items can be stored only by displacing existing items. Variation in the span is attributed on this theory to the fact that a unit can sometimes comprise more than one item. For example, two or more digits can sometimes be recoded as a familiar number which can then be stored as a unit. Indeed, if an individual has an exceptional familiarity with numbers he may have a digit span of fifteen or more. However, recoding digits into familiar numbers cannot account for the digit span of 80 recently achieved by one individual after extensive practice, who reported using both recoding and a hierarchical grouping strategy. At best, therefore, the slot theory describes the mechanism which normally determines the span.

    Two other interesting facts force another qualification to the slot theory. The span is reduced if the items of the sequence sound similar. For example, the sequence B V T G P is more difficult than the sequence S K L R N. If reproduction of the sequence involves retrieving the items from separate slots, why should this be so? Similarly, the span is smaller for long words than for short words, which is puzzling if each word is a unit and occupies a separate slot. With visual presentation, the effects of similarity both of sound and of word length vanish if the subject is asked to count aloud during presentation of the sequence. (At the same time, the counting task somewhat reduces the span.) This suggests that normally there is subvocal rehearsal of earlier items during presentation of later items of the sequence and that such rehearsal contributes to the span as normally measured.

    Since the slot theory postulates a special store for STM, by implication there must be a different store for long-term memory (LTM). Evidence for a two-store view of memory comes from memory pathology. Amnesia due to brain damage can take one of two forms. In the common form, STM is intact but LTM, in the sense of the ability to form new permanent memories, is impaired. In a rare form, which has only been identified quite recently, the reverse is found, with LTM intact but STM impaired. Clearly independent impairment of STM and LTM is highly consonant with the two-store theory. However, recent theory tends to postulate not one but several stores for the temporary storage of information. Indeed, evidence from the study of patients with impaired STM suggests that there are separate temporary stores for auditory speech sounds and for non-verbal sounds.

    Other evidence has been interpreted as showing that there are also temporary stores associated with touch and vision, although information from the latter fades in less than a second. There is also the possibility that the brain has temporary stores concerned with making responses. In the case of speech, for example, such a store might hold in readiness the codes for articulating several words and would substantially assist the smooth production of speech. Accordingly, the span of immediate memory (and STM generally) may reflect the output of one or more temporary stores, depending on circumstances. The common characteristic of these postulated stores is that each is of limited capacity and new information displaces old information. The slot theory of the span therefore seems too simple, although the facts it explains need to be accommodated in more complex accounts of the mechanisms underlying STM. If STM depends on specialized stores holding information over short intervals of time, the question arises of how information reaches the store responsible for LTM. One possibility is that there is a process of information transfer from these stores to the LTM store. If so, this process is presumably successful for only a proportion of the information entering the temporary stores, since we forget more than we remember. A second possibility is that information enters the LTM store directly at the time of perception, although at a slower rate than it enters the temporary stores. On this hypothesis, STM as we observe it may depend both on information retrieved from temporary stores and on information retrieved from the LTM store. At present, there is no decisive evidence favouring either possibility. Indeed, some theorists prefer to view memory as a single complex system. For example, the different properties of STM and LTM can be held to reflect, not the operation of different stores, but factors affecting the ease of retrieving stored information. This sort of theory is not implausible in view of the fact that problems associated with the retrieval of information from a storage system often impose major constraints on efficiency. However, the detailed facts about STM do seem to favour the view that specialized temporary stores are involved. Ideally, there would be physiological evidence to show how many stores underlie memory, but at present the evidence is indirect and difficult to interpret.

    (Published 1987)

    See chunking; information theory; memory: biological basis; memory and context.

    — John Brown

      Bibliography
    • Andrade, J., Baddeley, A. D., and Hitch, G. (2002). Working Memory in Perspective.
    • Baddeley, A. D. (1976). The Psychology of Memory.
    • Ericsson, K. A., Chase, W. G., and Faloon, S. (1980). 'Acquisition of a memory skill'. Science, 208/1.
    • Gathercole, S. (2001). Short-Term and Working Memory.

     
    Wikipedia: Short-term memory
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    Short-term memory (sometimes referred to as "primary memory" or "active memory") refers to the capacity for holding a small amount of information in mind in an active, readily available state for a short period of time. The duration of short-term memory (when rehearsal or active maintenance is prevented) is believed to be in the order of seconds. Estimates of short-term memory capacity limits vary from about 4 to about 9 items, depending upon the experimental design used to estimate capacity. A commonly-cited capacity is 7±2 elements. In contrast, long-term memory indefinitely stores a seemingly unlimited amount of information.

    Contents

    Existence of a separate store

    A classical model of memory developed in the 1960s assumed that all memories pass from a short-term to a long-term store after a small period of time. This model is referred to as the "modal model" and has been most famously detailed by Shiffrin.[1] The exact mechanisms by which this transfer takes place, whether all or only some memories are retained permanently, and indeed the existence of a genuine distinction between the two stores, remain controversial topics among experts.

    One form of evidence, cited in favor of the separate existence of a short-term store comes from anterograde amnesia, the inability to learn new facts and episodes. Patients with this form of amnesia, have intact ability to retain small amounts of information over short time scales (up to 30 seconds) but are dramatically impaired in their ability to form longer-term memories (a famous example is patient HM). This is interpreted as showing that the short-term store is spared from amnesia. A memory can remain in your short term memory bank for a total of 20 seconds.

    Other evidence comes from experimental studies showing that some manipulations (e.g., a distractor task, such as repeatedly subtracting a single-digit number from a larger number following learning) impair memory for the 3 to 5 most recently learned words of a list (presumably still held in short-term memory), while leaving recall for words from earlier in the list (presumably stored in long-term memory) unaffected; other manipulations (e.g., semantic similarity of the words) affect only memory for earlier list words,[2] but do not affect memory for the last few words in a list. These results show that different factors affect short term recall (disruption of rehearsal) and long-term recall (semantic similarity). Together, these findings show that long-term memory and short-term memory can vary independently of each other.

    Not all researchers agree that short-term and long-term memory are separate systems. Some theorists propose that memory is unitary over all time scales, from milliseconds to years[3]. Support for the unitary memory hypothesis comes from the fact that it has been difficult to demarcate a clear boundary between short-term and long-term memory. For instance, Tarnow shows that the recall probability vs. latency curve is a straight line from 6 to 600 seconds, with the probability of failure to recall only saturating after 600 seconds [4]. If there were really two different memory stores operating in this time frame, one could expect a discontinuity in this curve. Other research has shown that the detailed pattern of recall errors looks remarkably similar for recall of a list immediately after learning (presumably from short-term memory) and recall after 24 hours (necessarily from long-term memory)[5]

    Biological Basis

    It is proposed that short term memory is prolonged firing of neurons which depletes the Readily Releasable Pool (RRP) of neurotransmitter vesicles at presynaptic terminals[6]. The pattern of depleted presynaptic terminals represents the long term memory trace and the depletion itself is the short term memory. After the firing has slowed down, endocytosis causes short term memory to decay. If the endocytosis is allowed to finish (the memory is not activated again), the pattern of exhausted postsynaptic terminals becomes invisible and the short term memory disappears. The long term memory remains as the metastable pattern of the neuronal excitations.

    Broadbent's filter theory

    Broadbent's theories of selective attention and short-term memory were developed as digital computers were beginning to become available to the academic community, and were among the first to use computer analogies to make a serious contribution to the analysis of human cognition. They were combined to form what became known as the "single channel hypothesis". His Filter Model proposed that the physical characteristics (e.g., pitch, loudness) of an auditorily presented message were used to focus attention to only a single message. Broadbent's Filter model is referred to as an early selection model because irrelevant messages are filtered out before the stimulus information is processed for meaning. These and other theories were brought together in his 1958 book "Perception and Communication" which remains one of the classic texts of cognitive psychology[7].

    Broadbent's theory accounts for a theoretical filter device, which is located in between the incoming sensory register and the short-term memory storage. His theory is based upon the multi-storage paradigm of William James(1890) and later the Atkinson & Shiffrin's 'multi-store' memory model (1968). This filter functions together with a buffer, and enables the subject to handle two kinds of stimuli, presented at the same time. One of the inputs is allowed through the filter, while the other is waiting in the buffer for later processing. The filter prevents overloading of the limited capacity mechanism beyond the filter, which is the short-term memory[8]. It is based on the famous cocktail party problem of the British scientist Colin Cherry, who is trying to explain how we are able to focus our attention towards the stimuli which we find most interesting.[9]Broadbent comes up with the theory based on data from an experiment where three pairs of different digits are presented simultaneously, three digits in one ear and three in the other. Most participants recalled the digits ear by ear, rather than pair by pair. Thus, if 496 were presented to one ear and 852 to the other, the recall would be 496852 rather than 489562.

    Relationship with working memory

    The relationship between short-term memory and working memory is described differently by various theories, but it is generally acknowledged that the two concepts are distinct. Working memory is a theoretical framework that refers to structures and processes used for temporarily storing and manipulating information. As such, working memory might also be referred to as working attention. Short-term memory generally refers, in a theory-neutral manner, to the short-term storage of information, and it does not entail the manipulation or organization of material held in memory. Thus while there are short-term memory components to working memory models, the concept of short-term memory is distinct from these more hypothetical concepts. Within Baddeley's influential 1986 model of working memory there are two short-term storage mechanisms: the phonological loop and the visuospatial sketchpad. Most of the research referred to here involves the phonological loop, because most of the work done on short-term memory has used verbal material. In recent years, however, there has been a surge in research on visual short term memory[10], and also increasing work on spatial short term memory[11]

    Duration of short-term memory

    The limited duration of short-term memory immediately suggests that its contents spontaneously decay over time. The decay assumption is part of many theories of short-term memory, most notably Baddeley's model of working memory. The decay assumption is usually paired with the idea of rapid covert rehearsal: In order to overcome the limitation of short-term memory, and retain information for longer, information must be periodically repeated, or rehearsed — either by articulating it out loud, or by mentally simulating such articulation. In this way, the information will re-enter the short-term store and be retained for a further period.

    Several researchers, however, dispute that spontaneous decay plays any significant role in forgetting over the short term [12][13], and the evidence is far from conclusive[14].

    Authors doubting that decay causes forgetting from short-term memory often offer as an alternative some form of interference: When several elements (such as digits, words, or pictures) are held in short term memory simultaneously, their representations compete with each other for recall, or degrade each other. Thereby, new content gradually pushes out older content, unless the older content is actively protected against interference by rehearsal or by directing attention to it[15].

    Capacity of short-term memory

    Whatever the cause or causes of forgetting over the short term may be, there is consensus that it severely limits the amount of new information that we can retain over brief periods of time. This limit is referred to as the finite capacity of short-term memory. The capacity of short-term memory is often called memory span, in reference to a common procedure of measuring it. In a memory span test, the experimenter presents lists of items (e.g. digits or words) of increasing length. An individual's span is determined as the longest list length that he or she can recall correctly in the given order on at least half of all trials.

    In an early and highly influential article, The Magical Number Seven, Plus or Minus Two,[16] the psychologist George Miller suggested that human short-term memory has a forward memory span of approximately seven items plus or minus two. More recent research has shown that this "magical number seven" is roughly accurate for college students recalling lists of digits, but memory span varies widely with populations tested and with material used. For example, the ability to recall words in order depends on a number of characteristics of these words: fewer words can be recalled when the words have longer spoken duration; this is known as the word-length effect,[17] or when their speech sounds are similar to each other; this is called the phonological similarity effect.[18] More words can be recalled when the words are highly familiar or occur frequently in the language.[19] Recall performance is also better when all of the words in a list are taken from a single semantic category (such as sports) than when the words are taken from different categories.[20] According to the available evidence, the best overall estimate of short-term memory is about four pieces or "chunks" of information.[21]

    Chunking

    Chunking is the process with which we can expand our ability to remember things in the short term. Chunking is also a process by which a person organizes material into meaningful groups. Although the average person may only retain about four different units in short-term memory, chunking can greatly increase a person's recall capacity. For example, in recalling a phone number, the person could chunk the digits into three groups: first, the area code (such as 215), then a three-digit chunk (123) and lastly a four-digit chunk (4567). This method of remembering phone numbers is far more effective than attempting to remember a string of 10 digits.

    Practice and the usage of existing information in long-term memory can lead to additional improvements in one's ability to use chunking. In one testing session, an All-American cross-country runner was able to recall a string of 79 digits after hearing them only once by chunking them into different running times (e.g. the first four numbers were 1518, a three-mile time.)[22]

    See also

    References

    Notes

    1. ^ Atkinson and Shiffrin, 1968
    2. ^ Davelaar, Goshen-Gottstein, Haarmann & Usher, 2005
    3. ^ Brown, G. D. A., Neath, I., & Chater, N. (2007). A ratio model of scale-invariant memory and identification. Psychological Review, 114, 539-576.
    4. ^ Tarnow, 2007
    5. ^ Nairne, J. S., & Dutta, A. (1992). Spatial and temporal uncertainty in long-term memory. Journal of Memory and Language, 31, 396-407.
    6. ^ Tarnow, Eugen (2008)
    7. ^ Broadbent, D. (1958). Perception and Communication. London: Pergamon Press.
    8. ^ Broadbent, D. (1958). Perception and Communication. London: Pergamon Press.
    9. ^ Cherry, E.C.(1958)Some experiments on the recognition of speech with one and two ears. Journal of the acoustical society of America,25,975-979
    10. ^ Luck, S. J., & Vogel, E. K. (1997). The capacity of visual working memory for features and conjunctions. Nature, 390, 279-281.
    11. ^ Parmentier, F. B. R., Elford, G., & Maybery, M. (2005). Transitional information in spatial serial memory: path characteristics affect recall performance. Journal of Experimental Psychology: Learning, Memory, and Cognition, 31, 412-427.
    12. ^ Lewandowsky, S., Duncan, M., & Brown, G. D. A. (2004). Time does not cause forgetting in short-term serial recall. Psychonomic Bulletin & Review, 11, 771-790.
    13. ^ Nairne, J. S. (2002). Remembering over the short-term: The case against the standard model. Annual Review of Psychology, 53, 53-81.
    14. ^ Jonides, J., Lewis, R. L., Nee, D. E., Lustig, C. A., Berman, M. G., & Moore, K. S. (2008). The mind and brain of short-term memory. Annual Review of Psychology, 59, 193-224.
    15. ^ Oberauer, K., & Kliegl, R. (2006). A formal model of capacity limits in working memory. Journal of Memory and Language, 55, 601-626.
    16. ^ Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63, 81-97.
    17. ^ Baddeley, Thomson & Buchanan, 1975
    18. ^ Conrad & Hull, 1964
    19. ^ Poirier & Saint-Aubin, 1996
    20. ^ Poirier & Saint-Aubin, 1995
    21. ^ Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behavioral and Brain Sciences, 24, 97-185.
    22. ^ Ericsson, Chase & Faloon, 1980

    Bibliography


    • Baddeley, A. D., Thomson, N., & Buchanan, M. (1975). Word length and the structure of short term memory. Journal of Verbal Learning and Verbal Behavior, 14, pp. 575–589.
    • Conrad, R., & Hull, A. J. (1964). Information, acoustic confusion and memory span. British Journal of Pychology, 55, pp. 429–432.
    • Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behavioral and Brain Sciences, 24, pp. 1–185.
    • Davelaar, E. J., Goshen-Gottstein, Y., A., A., Haarmann, H. J., & Usher, M. (2005): The demise of short-term memory revisited: empirical and computational investigation of recency effects. Psychological Review, 112, pp. 3–42.
    • Ericsson, K. A., Chase, W. G., & Faloon, S. (1980). Acquisition of a memory skill. Science, 208, pp. 1181–1182
    • Lehrl, S., & Fischer, B. (1988): The basic parameters of human information processing: their role in the determination of intelligence. Personality and individual Differences, 9, pp. 883–896. ([1])
    • Miller, G. (1956): "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information", Psychological Review, vol. 63 pp. 81–97 ([2])
    • Poirier, M., & Saint-Aubin, J. (1996). Immediate serial recall, word frequency, item identity and item position. Canadian Journal of Experimental Psychology, 50, pp. 408–412.
    • Poirier, M., & Saint-Aubin, J. (1995). Memory for related and unrelated words: Further evidence on the influence of semantic factors in immediate serial recall. Quarterly Journal of Experimental Psychology, 48A, pp. 384–404.
    • Schacter, D. L. (1997): Searching for Memory: The Brain, the Mind, and the Past. ISBN 0-465-07552-5.
    • Tarnow, Eugen (2005): The Short Term Memory Structure In State-Of-The Art Recall/Recognition Experiments of Rubin, Hinton and Wentzel. ([3])
    • Tarnow, Eugen (2008): Short Term Memory May Be the Depletion of the Readily Releasable Pool of Presynaptic Neurotransmitter Vesicles. ([4])

    External links

    v • d • e
    Neurophysiology - Memory
    Long-term memory
    Short-term memory
    Sensory memory

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