The project will test the hypothesis that there are two separate attention processes mediated by posterior association cortex: One which conjoins visual features in the process of object recognition, an a second which selects objects for action. In addition the studies will investigate whether these two processes are independent and, if so, identify the neural substrate underlying each. Most of the research will involve experiments that test the attentional abilities of patients with lesions of posterior association cortex. One series of experiments will investigate patients with clinical extinction to determine the degree to which simple visual features are processed in the unattended field in comparison to the ipsilesional field. It is predicted that processing of simple features in the contralesional field will be comparable to that for features in the ipsilesional field, and that the deficit in extinction will reflect primarily a failure to transfer the percept to the action system. A second series of studies will test patients without clinical extinction in a task to examine illusory conjunctions, a phenomenon in which information from different objects is erroneously combined. It is predicted that these patients will show a deficit in feature integration in the contralesional field.
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