Editing Visual short-term memory (section)

==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 -->