View source for Visual short-term memory

In the study of [[visual perception|vision]], '''visual short-term memory''' ('''VSTM''') is one of three broad memory systems including [[iconic memory]] and [[long-term memory]]. VSTM is a type of [[short-term memory]], but one limited to information within the visual domain.

The term VSTM refers in a theory-neutral manner to the non-permanent storage of visual information over an extended period of time.<ref>{{Cite journal |last1=Buss |first1=Aaron T. |last2=Ross-Sheehy |first2=Shannon |last3=Reynolds |first3=Greg D. |date=2018-10-01 |title=Visual working memory in early development: a developmental cognitive neuroscience perspective |journal=Journal of Neurophysiology |volume=120 |issue=4 |pages=1472–1483 |doi=10.1152/jn.00087.2018 |pmid=29897858 |s2cid=49189631 |issn=0022-3077|doi-access=free }}</ref> The [[visuospatial sketchpad]] is a VSTM subcomponent within the theoretical model of [[working memory]] proposed by Alan Baddeley; in which it is argued that a working memory aids in mental tasks like planning and comparison.<ref>{{Cite journal |last1=Buss |first1=Aaron T. |last2=Ross-Sheehy |first2=Shannon |last3=Reynolds |first3=Greg D. |date=2018-10-01 |title=Visual working memory in early development: a developmental cognitive neuroscience perspective |journal=Journal of Neurophysiology |volume=120 |issue=4 |pages=1472–1483 |doi=10.1152/jn.00087.2018 |pmid=29897858 |s2cid=49189631 |issn=0022-3077|doi-access=free }}</ref><ref>{{Cite journal |last=Logie |first=Robert |date=1988-04-01 |title=Working memory, Alan Baddeley, Oxford University Press, Oxford 1986. No. of pages: 289. Price £30.00 (Hardback), ISBN 0 19 852116 2 |url=https://onlinelibrary.wiley.com/doi/10.1002/acp.2350020209 |journal=Applied Cognitive Psychology |language=en |volume=2 |issue=2 |pages=166–168 |doi=10.1002/acp.2350020209|url-access=subscription }}</ref> Whereas iconic memories are fragile, decay rapidly, and are unable to be actively maintained, visual short-term memories are robust to subsequent stimuli and last over many seconds. VSTM is distinguished from long-term memory, on the other hand, primarily by its very limited capacity.<ref>{{Cite journal |last1=Buss |first1=Aaron T. |last2=Ross-Sheehy |first2=Shannon |last3=Reynolds |first3=Greg D. |date=2018-10-01 |title=Visual working memory in early development: a developmental cognitive neuroscience perspective |journal=Journal of Neurophysiology |volume=120 |issue=4 |pages=1472–1483 |doi=10.1152/jn.00087.2018 |pmid=29897858 |s2cid=49189631 |issn=0022-3077|doi-access=free }}</ref><ref>{{Citation |last1=Baddeley |first1=Alan D. |title=Working Memory |date=1974-01-01 |url=https://www.sciencedirect.com/science/article/pii/S0079742108604521 |volume=8 |pages=47–89 |editor-last=Bower |editor-first=Gordon H. |publisher=Academic Press |language=en |doi=10.1016/s0079-7421(08)60452-1 |access-date=2022-05-16 |last2=Hitch |first2=Graham|series=Psychology of Learning and Motivation |isbn=9780125433082 |url-access=subscription }}</ref>

==Overview==

The introduction of [[stimulation|stimuli]] which were hard to verbalize, and unlikely to be held in [[long-term memory]], revolutionized the study of VSTM in the early 1970s.<ref name="Cermak 1971">{{cite journal |doi=10.3758/BF03329095|title=Short-term recognition memory for complex free-form figures |journal=Psychonomic Science |volume=25|issue=4|pages=209–211|year=1971|last1=Cermak|first1=Gregory W.|doi-access=free}}</ref><ref name="Phillips 1974">{{cite journal | last1 = Phillips | first1 = W.A. | year = 1974 | title = On the distinction between sensory storage and short-term visual memory | journal = Perception & Psychophysics | volume = 16 | issue = 2| pages = 283–290 | doi = 10.3758/bf03203943 | doi-access = free }}</ref><ref name="Phillips 1971">{{cite journal | last1 = Phillips | first1 = W.A. | last2 = Baddeley | first2 = A.D. | year = 1971 | title = Reaction time and short-term visual memory | journal = Psychonomic Science | volume = 22 | issue = 2| pages = 73–74 | doi = 10.3758/bf03332500 | doi-access = free }}</ref> The basic experimental technique used required observers to indicate whether two matrices,<ref name="Phillips 1974"/><ref name="Phillips 1971"/> or figures,<ref name="Cermak 1971"/> separated by a short temporal interval, were the same. The finding that observers were able to report that a change had occurred, at levels significantly above chance, indicated that they were able to encode aspect of the first stimulus in a purely visual store, at least for the period until the presentation of the second stimulus. However, as the stimuli used were complex, and the nature of the change relatively uncontrolled, these experiments left open various questions, such as:
#whether only a subset of the perceptual dimensions comprising a visual stimulus are stored (e.g., spatial frequency, luminance, or contrast)
#whether perceptual dimensions are maintained in VSTM with greater fidelity than others
#the nature by which these dimensions are encoded (i.e., are perceptual dimensions encoded within separate, parallel channels, or are all perceptual dimensions stored as a single bound entity within VSTM?).

==Set-size effects==
Much effort has been dedicated to investigating the capacity limits of VSTM. In a typical change-detection task, observers are presented with two arrays, composed of a number of stimuli. The two arrays are separated by a short temporal interval, and the task of observers is to decide if the first and second arrays are identical, or whether one item differs across the two displays.{{efn|e.g., {{harvnb |Luck |Vogel |1997}}.}} Performance is critically dependent on the number of items in the array. While performance is generally almost perfect for arrays of one or two items, correct responses invariably decline in a monotonic fashion as more items are added. Different theoretical models have been put forward to explain limits on VSTM storage, and distinguishing between them remains an active area of research.

==Models of capacity limits==

===Slot models===
A prominent class of model proposes that observers are limited by the total number of items which can be encoded, either because the capacity of VSTM itself is limited.{{efn|e.g., {{harvnb |Cowan |2001}}; {{harvnb |Luck |Vogel |1997}}; {{harvnb |Pashler |1988}}.}} This type of model has obvious similarities to urn models used in probability theory.{{efn|See, for example, {{harvnb |Mendenhall |1967}}.{{Full citation needed|date=May 2022}}<!-- There are a number of works by people named Mendenhall published in 1967. -->}} In essence, an urn model assumes that VSTM is restricted in storage capacity to only a few items, ''k'' (often estimated to lie in the range of three-to-five in adults, though fewer in children<ref>{{cite journal | last1 = Riggs | first1 = K.J. | last2 = McTaggart | first2 = J. | last3 = Simpson | first3 = A. | year = 2006 | title = Changes in the capacity of visual working memory in 5- to 10-year-olds | journal = Journal of Experimental Child Psychology | volume = 95 | issue = 1| pages = 18–26 | doi = 10.1016/j.jecp.2006.03.009 | pmid = 16678845 }}</ref>). The probability that a suprathreshold change will be detected is simply the probability that the change element is encoded in VSTM (i.e., ''k''/''N''). This capacity limit has been linked to the posterior parietal cortex, the activity of which initially increases with the number of stimuli in the arrays, but saturates at higher set-sizes.<ref>{{cite journal |doi=10.1038/nature02466 |pmid=15085133 |title=Capacity limit of visual short-term memory in human posterior parietal cortex |journal=Nature |volume=428 |issue=6984 |pages=751–754 |year=2004 |last1=Todd |first1=J. Jay |last2=Marois |first2=René |bibcode=2004Natur.428..751T |s2cid=4415712}}</ref> Although urn models are used commonly to describe performance limitations in VSTM,{{efn|e.g., {{harvnb |Luck |Vogel |1997}}; {{harvnb |Pashler |1988}}; {{harvnb |Sperling |1960}}.}} it is only recently that the actual structure of items stored has been considered. Luck and colleagues have reported a series of experiments designed specifically to elucidate the structure of information held in VSTM.<ref>{{cite journal | last1 = Luck | first1 = S.J. | last2 = Vogel | first2 = E.K. | year = 1997 | title = The capacity of visual working memory for features and conjunctions | journal = Nature | volume = 390 | issue = 6657| pages = 279–281 | doi = 10.1038/36846 | pmid = 9384378 | bibcode = 1997Natur.390..279L | s2cid = 205025290 }}</ref> This work provides evidence that items stored in VSTM are coherent objects, and not the more elementary features of which those objects are composed.

===Noise models===
An alternative framework has more been put forward by [[Patrick Wilken|Wilken]] and Ma who suggest that apparent capacity limitations in VSTM are caused by a monotonic decline in the quality of the internal representations stored (i.e., monotonic increase in noise) as a function of set-size. In this conception capacity limitations in memory are not caused by a limit on the number of things that can be encoded, but by a decline in the quality of the representation of each thing as more things are added to memory. In their 2004 experiments, they varied color, spatial frequency, and orientation of objects stored in VSTM using a signal detection theory approach.{{efn|See also the closely related work by {{harvnb|Palmer|1990}}.}} The participants were asked to report differences between the visual stimuli presented to them in consecutive order. The investigators found that different stimuli were encoded independently and in parallel, and that the major factor limiting report performance was [[neuronal noise]] (which is a function of visual set-size).<ref name="Wilken 2004">{{cite journal | last1 = Wilken | first1 = P. | last2 = Ma | first2 = W.J. | year = 2004 | title = A detection theory account of change detection | journal = J Vis | volume = 4 | issue = 12| pages = 1120–1135 | doi = 10.1167/4.12.11 | pmid = 15669916 | doi-access = free }}</ref><!-- Applies to the whole paragraph -->

Under this framework, the key limiting factor on working memory performance is the precision with which visual information can be stored, not the number of items that can be remembered.<ref name="Wilken 2004"/> Further evidence for this theory was obtained by Bays and Husain using a discrimination task. They showed that, unlike a "slot" model of VSTM, a signal-detection model could account both for discrimination performance in their study and previous results from change detection tasks.{{efn|e.g., {{harvnb |Luck |Vogel |1997}}.}} These authors proposed that VSTM is a flexible resource, shared out between elements of a visual scene—items that receive more resource are stored with greater precision. In support of this, they showed that increasing the salience of one item in a memory array led to that item being recalled with increased resolution, but at the cost of reducing resolution of storage for the other items in the display.<ref>{{cite journal | last1 = Bays | first1 = P.M. | last2 = Husain | first2 = M. | year = 2008 | title = Dynamic shifts of limited working memory resources in human vision | journal = Science | volume = 321 | issue = 5890| pages = 851–854 | doi = 10.1126/science.1158023 | pmc = 2532743 | pmid = 18687968 | bibcode = 2008Sci...321..851B }}</ref><!-- supports the statements from where it mentions Bays and Husain onwards -->

==Psychophysical models==
Psychophysical experiments suggest that information is encoded in VSTM across multiple parallel channels, each channel associated with a particular perceptual attribute.<ref>{{cite journal | last1 = Magnussen | first1 = S | year = 2000 | title = Low-level memory processes in vision | journal = Trends in Neurosciences | volume = 23 | issue = 6| pages = 247–251 | doi = 10.1016/s0166-2236(00)01569-1 | pmid = 10838593 | s2cid = 16231057 }}</ref> Within this framework, a decrease in an observer's ability to detect a change with increasing set-size can be attributed to two different processes: 
#if decisions are made across different channels, decreases in performance are typically small, and consistent with decreases expected when making multiple independent decisions<ref name="Greenlee 1993">{{cite journal | last1 = Greenlee | first1 = M.W. | last2 = Thomas | first2 = J.P. | year = 1993 | title = Simultaneous discrimination of the spatial frequency and contrast of periodic stimuli | journal = Journal of the Optical Society of America A | volume = 10 | issue = 3| pages = 395–404 | doi = 10.1364/josaa.10.000395 | pmid = 8473947 | bibcode = 1993JOSAA..10..395G }}</ref><ref>{{cite journal | last1 = Vincent | first1 = A. | last2 = Regan | first2 = D. | year = 1995 | title = Parallel independent encoding of orientation, spatial frequency, and contrast | journal = Perception | volume = 24 | issue = 5| pages = 491–499 | doi = 10.1068/p240491 | pmid = 7567425 | s2cid = 25950156 }}</ref>
#if multiple decisions are made within the same channel, the decrease in performance is much greater than expected on the basis of increased decision-noise alone, and is attributed to interference caused by multiple decisions within the same perceptual channel.<ref>{{cite journal | last1 = Magnussen | first1 = S. | last2 = Greenlee | first2 = M.W. | year = 1997 | title = Competition and sharing of processing resources in visual discrimination | journal = Journal of Experimental Psychology: Human Perception and Performance | volume = 23 | issue = 6| pages = 1603–1616 | doi = 10.1037/0096-1523.23.6.1603 | pmid = 9425670 }}</ref>

However, the Greenlee-Thomas model<ref name="Greenlee 1993"/> suffers from two failings as a model for the effects of set-size in VSTM. First, it has only been empirically tested with displays composed of one or two elements. It has been shown repeatedly in various experimental paradigms that set-size effects differ for displays composed of a relatively small number of elements (i.e., 4 items or less), and those associated with larger displays (i.e., more than 4 items). The Greenlee-Thomas model offers no explanation for why this might be so. Second, while Magnussen, Greenlee, and Thomas<ref>{{harvnb |Magnussen |Greenlee |Thomas |1997}}</ref>{{Full citation needed|date=May 2022}}<!-- Can only find the paper by Magnussen and Greenlee in 1997 (cited already in this article), none by all three --> are able to use this model to predict that greater interference will be found when dual decisions are made within the same perceptual dimension, rather than across different perceptual dimensions, this prediction lacks quantitative rigor, and is unable to accurately anticipate the size of the threshold increase, or give a detailed explanation of its underlying causes.

In addition to the Greenlee-Thomas model, there are two other prominent approaches for describing set-size effects in VSTM. These two approaches can be referred to as sample size models,<ref>{{cite journal | last1 = Palmer | first1 = J | year = 1990 | title = Attentional limits on the perception and memory of visual information | journal = Journal of Experimental Psychology: Human Perception and Performance | volume = 16 | issue = 2| pages = 332–350 | doi = 10.1037/0096-1523.16.2.332 | pmid = 2142203 }}</ref> and urn models.{{efn|e.g., {{harvnb |Pashler |1988}}.}} They differ from the Greenlee-Thomas model by: 
#ascribing the root cause of set-size effects to a stage prior to decision making
#making no theoretical distinction between decisions made in the same, or across different, perceptual dimensions.

==Intermediate visual store==
There is some evidence of an [[intermediate visual store]] with characteristics of both iconic memory and VSTM.<ref>{{cite journal |title=Are There Multiple Visual Short-Term Memory Stores? |journal=PLOS ONE|volume=3 |issue=2|pages=e1699 |doi=10.1371/journal.pone.0001699 |pmid=18301775|pmc=2246033 |year=2008 |last1=Sligte |first1=Ilja G.|last2=Scholte|first2=H. Steven|last3=Lamme|first3=Victor A. F.|bibcode=2008PLoSO...3.1699S |doi-access=free}}</ref> This intermediate store is proposed to have high capacity (up to 15 items) and prolonged memory trace duration (up to 4 seconds). It coexists with VSTM but unlike it visual stimuli can overwrite the contents of its visual store.<ref>{{cite journal | last1 = Pinto | first1 = Y. | last2 = Sligte | first2 = I.S. | last3 = Shapiro | first3 = K.L. | last4 = Lamme | first4 = V.A.F. | year = 2013 | title = Fragile Visual Short-Term Memory is an object-based and location-specific storage | journal = Psychonomic Bulletin & Review | volume = 20 | issue = 4| pages = 732–739 | doi = 10.3758/s13423-013-0393-4 | pmid = 23456410 | doi-access = free }}</ref> Further studies suggests an involvement of [[visual area V4]] in the retention of information about the color of the stimulus in visual working memory,<ref>{{cite journal |doi=10.1523/JNEUROSCI.0784-09.2009|pmid=19515911|pmc=6665414|title=V4 Activity Predicts the Strength of Visual Short-Term Memory Representations|journal=Journal of Neuroscience |volume=29 |issue=23 |pages=7432–7438|year=2009 |last1=Sligte |first1=I. G.|last2=Scholte|first2=H. S.|last3=Lamme|first3=V. A. F.}}</ref><ref name="Kozlovskiy2021">{{cite book |last1=Kozlovskiy |first1=Stanislav |last2=Rogachev |first2=Anton |chapter=How Areas of Ventral Visual Stream Interact when We Memorize Color and Shape Information |series=Advances in Intelligent Systems and Computing |title=Advances in Cognitive Research, Artificial Intelligence and Neuroinformatics |date=2021 |volume=1358 |issue=95–100 |pages=95–100 |doi=10.1007/978-3-030-71637-0_10 |chapter-url=https://link.springer.com/chapter/10.1007/978-3-030-71637-0_10 |publisher=Springer-Nature |isbn=978-3-030-71636-3 |s2cid=234902744 |issn=2194-5357}}</ref> and the role of the VO1 area for retaining information about its shape.<ref name="Kozlovskiy2021" /> It has been shown that in the VO2 region all characteristics of the stimulus retained in memory are combined into a holistic image.<ref name="Kozlovskiy2021" />

==The function of visual short-term memory representations==
VSTM is thought{{by whom|date=March 2019}} to be the visual component of the working memory system, and as such it is used as a buffer for temporary information storage during the process of naturally occurring tasks. But what naturally occurring tasks actually require VSTM? Most work on this issue has focused on the role of VSTM in bridging the sensory gaps caused by saccadic eye movements. These sudden shift of gaze typically occur 2–4 times per second, and vision is briefly suppressed while the eyes are moving. Thus, the visual input consists of a series of spatially shifted snapshots of the overall scene, separated by brief gaps. Over time, a rich and detailed long-term memory representation is constructed from these brief glimpses of the input, and VSTM is thought{{by whom|date=March 2019}} to bridge the gaps between these glimpses and to allow the relevant portions of one glimpse to be aligned with the relevant portions of the next glimpse. Both spatial and object VSTM systems may play important roles in the integration of information across eye movements. Eye movements are also affected by VSTM representations. The constructed representations held in VSTM can affect eye movements even when the task does not explicitly require eye movements: the direction of small [[microsaccade]]s point towards the location of objects in VSTM.<ref>{{cite journal |last1=Martinez-Conde |first1=S |last2=Alexander |first2=R |title=A gaze bias in the mind's eye |journal=Nature Human Behaviour |date=2019 |volume=3 |issue=5 |pages=424–425 |doi=10.1038/s41562-019-0546-1 |pmid=31089295 |s2cid=71148025 }}</ref>

==See also==
* [[Attention]]
* [[Attention versus memory in prefrontal cortex]]
* [[Change blindness]]
* [[Memory]]
* [[Perception]]

==Notes==
{{notelist}}

==References==
{{Reflist}}

===Sources===
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[[Category:Consciousness]]
[[Category:Vision]]
[[Category:Memory]]