DISSOCIABLE COGNITIVE AND NEURAL MECHANISMS OF UNILATERAL VISUAL NEGLECT

We administered two experimental tasks to 16 patients with neglect fol lowing unilateral right hemisphere strokes, designed to probe processi ng of information in the neglected left visual field. A semantic primi ng/lexical decision task examined implicit processing of stimuli prese nted to the neglected field, and a discrimination task required explic it recognition of the same stimuli. We grouped patients according to t hree patterns of performance: (1) poor discrimination in the left visu al field but intact priming, (2) normal priming and discrimination in both fields, and (3) normal priming but poor discrimination in both fi elds. Although patients in group 1 had posterior lesions, patients in groups 2 and 3 had extensive deep anterior lesions. These results sugg est that the clinical phenomenon of unilateral visual neglect can be t he surface manifestation of deficits in two different and interacting processes-attentional processes (group 1) and intentional processes (g roup 2)-or it may be a global attentional disturbance superimposed on these deficits (group 3).