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.

Object perception
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.

Conscious awareness
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.

Visual memory
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.