|Research in my lab is concerned
with visual attention, object perception and memory. We explore
the nature of the limits to human perception, the information-processing
that results in the perception of objects and events, and the
nature of the representations that underlie both conscious experience
and implicit memory, shown in perceptual priming. We mainly
use behavioral methods, but we are interested in relating our
findings to the brain. We study patients with brain damage,
and collaborate in studies using brain imaging or evoked responses.
Topics of research include the following:
Visual attention, search, and the "binding problem"
What kinds of information are available without focusing attention
when we are presented with multi-element arrays and what kinds
require focused attention? What variables control the deployment
of spatial attention? Physiological findings suggest that
the visual system sets up multiple specialized "maps"
coding different aspects of the scene; how then do we combine
information about the separate features of objects. Experimental
tasks include visual search, and divided attention paradigms
in which irrelevant stimuli evoke competing responses. A detailed
study of a patient with bilateral parietal lesions linked
his major deficits in spatial localization to the large number
of binding errors that he also makes.
We use novel shapes to probe the nature of the representations
that are formed in the absence of any matching representations
or prior knowledge. One project explores generalization from
specific learned orientations of novel objects to its three-dimensional
shape. We are also interested in the role of attention in
forming object representations, testing for example whether
attention is necessary for the perception of occlusion relations,
identity and meaning.
Global attention and perception of statistical properties
We are testing the hypothesis that when attention is spread
over sets of similar items, we automatically form representations
of their statistical properties, summarizing their mean color,
size, shape, direction of motion and so on, as well as the
variance of those properties. However, the detailed binding
is lost for items within the set. Feature analysis may also
rapidly give the gist of the scene, although focused attention
is needed to individuate the objects and specify the conjunctions
that are present.
We explore some conditions under which information is taken
in without being consciously accessible. For example, in a
phenomenon known as the "attentional blink", subjects
search for two targets in a stream of visual stimuli presented
successively at high rates, and appear to be blind to the
second of two targets when they have just detected the first.
Awareness can also be blocked in "repetition blindness":
a repeated stimulus in a rapid sequential stream is much less
likely to be seen than a nonrepeated one.
We study visual working memory for features and for binding
in conscious recall. Priming studies in my lab have shown
that detailed representations of unattended shapes are also
formed unconsciously and can last for weeks without any explicit
memory of them. We are studying the nature of these representations,
the conditions under which they are formed, and their relation
to explicit memories formed with attention. We also study
perceptual learning through the effects of repeated exposure
and practice in visual tasks.