ONLINE BRAIN POTENTIAL CORRELATES OF RIGHT PERIETAL PATIENTS ATTENTIONAL DEFICIT

EEG potentials evoked by cues and targets were recorded in Posner's vi sual cueing task from 10 patients with lesions of the right parietal c ortex and from age-matched healthy subjects. The patients' Nl componen t evoked by left-side cues was reduced at the right-parietal recording site, suggesting a general impairment in processing left-side visual input. As usual, patients' keypress responses were delayed when left t argets were preceded by right cues. There were two correlates of this delay in the patients' EEG potentials evoked by the critical combinati on of right cue/left target: their mean amplitude 160-280 ms after tar get onset ('Nd') was less negative than with other combinations of cue and target, and the following frontal P3000 was enhanced. The Nd redu ction seems to be an on-line measure of patients' momentary decrease o f attention for the left hemifield, while the frontal P300 might refle ct the patients' attempts at reorienting. In conclusion, different com ponents were sensitive to different aspects of the patients' disorder, suggesting the utility of this approach for developing detailed hypot heses on the mechanisms of attentional deficits involved in visual ext inction and neglect.