Talk Announcement: Ed Awh

Dr. Ed Awh
Department of Psychology
University of Oregon, Institute of Neuroscience

Complexity, categories, and capacity in visual working memory

Monday, November 19, 2007
4:00pm
SSPA 2112

Abstract
Several paradigms have converged on a capacity limit of about 3-4
items in visual working memory. This limit exhibits robust
correlations with a broad range of intelligence measures, motivating
an interest in the basic determinants of memory capacity. For
example, performance in the change detection paradigm – a widely used
measure of capacity – declines as stimulus complexity increases. We
have found, however, that increased complexity is typically associated
with increased similarity between the potential sample and test items,
raising the possibility that change detection with complex objects was
limited by the resolution rather than by the number of items
represented in working memory. Indeed, when resolution-based errors
were minimized by reducing sample/test similarity, capacity estimates
for the most complex objects were equivalent to that for the simplest
objects (r = .84). This conclusion was also supported via
measurements of the CDA (contralateral delay activity) waveform, an
event-related potential waveform that provides an online measure of
the number of items maintained during the delay period. CDA amplitude
was equivalent for simple and complex objects. By contrast, a
separate measure of neural activity during the comparison stage of the
task was sensitive to object complexity, though uncorrelated with CDA
amplitude. Thus, visual working memory represents a fixed number of
objects, regardless of complexity. Importantly, analyses of
individual differences suggest that limits in the number and
resolution of representations in working memory represent distinct
aspects of memory ability. Finally, I will present further evidence
that this number/resolution dichotomy is useful for understanding how
perceptual expertise improves memory performance, the relationship
between memory ability and measures of fluid intelligence, and the
factors that influence mnemonic resolution in multi-item displays.