Editing Visual short-term memory (section)

==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.