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Abstract:
Although decades of research have indicated that
approximately 7 items can be stored in verbal working memory, the
storage capacity of
visual
working memory has not yet been established for simple,
suprathreshold features or for conjunctions of features. In this
study, we examined the capacity of visual working memory in a
successive-comparison paradigm in which subjects viewed two
stimulus arrays on each trial, separated by a 900-ms delay, and
then indicated whether the two arrays were identical or differed in
terms of a single feature. The accuracy of this discrimination was
assessed as a function of the number of items in the stimulus array
to determine how many items could be accurately retained in working
memory. The results indicated that subjects could retain
information about only 4 colors or orientations in visual working
memory at one time. However, they could retain both the color
and
the orientation of 4 objects, indicating that visual working
memory stores integrated objects rather than individual features.
Indeed, objects defined by a conjunction of 4 features could be
retained in working memory just as well as single-feature objects,
allowing 16 individual features to be retained when distributed
across 4 objects. In addition, objects defined by two colors could
be retained in working memory just as easily as objects defined by
a single color. These results can be explained by a mechanism that
binds features together in working memory by means of correlated
neural firing.
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