SPATIAL NEGLECT AND MECHANISMS OF ATTENTION

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DESCRIPTION (Applicant's Abstract): The neglect syndrome constitutes a failure to report, respond or orient to novel or meaningful stimuli where the failure is not attributable to a pure sensory or motor deficit. Over 62,000 new patients per year evidence neglect. Patients with neglect do not profit from rehabilitation to the same degree as those without neglect. This is due, in part, to the fact that neglect is a heterogenous syndrome. Remediation strategies often treat neglect as a single presentation and fail to consider individual variation. In contrast, the treatment of aphasia is more efficacious as treatment strategies are predicated on performance subtypes. Studies in this proposal attempt to identify performance subtypes in neglect so that more appropriate treatment strategies can be developed. Performance subtypes will be associated with lesion location to elucidate the mechanisms of spatial attention. Although neglect encompasses a broad spectrum of deficits, it is primarily viewed as a disorder of attention. Performance subtypes within three domains of attentional processing sustained attention, attentional capacity and attentional orientation are investigated in this proposal. Patients with neglect are selected for study on the basis of lesion location. Sustained attention is defined by a subjects ability to fixate a target stimulus and simultaneously monitor stimuli in peripheral vision (i.e., an examination of the Troxler fading phenomenon). Sustained attention is predicted to be deficit following posterior cortical lesions, whereas, the ability to inhibit sustained attention will be deficit following anterior cortical lesions. Attentional capacity is defined by the patient's ability to attend to a whole stimulus. The size of the patient's error is used to measure attentional capacity. Anterior cortical lesions are predicted to produce limitations in attentional capacity that do not change according to the hemispatial location of the stimulus. Attentional orientation in neglect is defined by the spatial direction of the neglect error. Posterior cortical lesions are predicted to produce orientation biases that are fixed in one spatial dimension. Orientation biases following anterior lesions will vary according to stimulus location and directional cuing. 80 patients with neglect following unilateral, ischemic infarctions and 40 normal controls will be studied to test these hypotheses. These studies will increase knowledge regarding the localization of attentional operations. They will facilitate neglect rehabilitation through identifying subtypes of performance.