Won Mok Shim

Massachusetts Institute of Technology

The human visual system is constantly confronted with an overwhelming amount of
information, only part of which can be processed in complete detail. What sets this limit in our
cognitive processing? In this talk I will examine two cognitive mechanisms which are highly
limited in capacity - attentive tracking and visual working memory - using psychophysical and
brain imaging methods. Conventional wisdom says that attention is limited in the number of
foci, and working memory is limited in slots, with the number of slots inversely related to object
complexity. I will show evidence from our studies that these views need to be revised.
More specifically, these studies suggest: 1) Capacity limitation from attentive tracking originates
not only from a number of locations, but also from factors such as spacing among
multiple attentional foci and speed of the target and distractors. These two factors are
dissociated in the fronto-parietal attention network. 2) Complex objects do not always exhaust
visual working memory more quickly than simple objects when memory-to-test
similarity is matched.