The term VSTM refers in a theory-neutral manner to the non-permanent storage of visual information over an extended period of time.
However, as the stimuli used were complex, and the nature of the change relatively uncontrolled, these experiments left open various questions, such as: Much effort has been dedicated to investigating the capacity limits of VSTM.
Different theoretical models have been put forward to explain limits on VSTM storage, and distinguishing between them remains an active area of research.
[c] 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[9]).
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.
[10] Although urn models are used commonly to describe performance limitations in VSTM,[d] it is only recently that the actual structure of items stored has been considered.
In their 2004 experiments, they varied color, spatial frequency, and orientation of objects stored in VSTM using a signal detection theory approach.
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).
[12] 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.
Second, while Magnussen, Greenlee, and Thomas[18][full citation needed] 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.
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.