Journal of Cognitive Neuroscience
The aim of the present study was to assess the relationship between overt and covert orienting of attention in visual neglect patients with parietal and fronto-parietal lesions. Two stimuli were presented at eccentricities of 8° or 20° to the left (LVF) or right (RVF) visual fields and the patient was required to maintain fixation on the central mark and to respond only manually upon the appearance of the stimulus. Neglect patients with fronto-parietal lesion showed a lack of oculomotor control and the presence of leftward eye movements without corresponding attentional shifts. Neglect patients with parietal lesions did not show this phenomenon. They rarely responded ocularly and manually to LVF stimuli, whereas they were unable to inhibit an automatic ocular orienting reaction towards RVF stimuli. When a RVF stimuli triggered both ocular and attentional shifts, the pattern of responses revealed a retinal eccentricity effect. Patients were more accurate to respond to stimuli located at 8° than 20°. In contrast, when a RVF stimuli triggered only attentional shifts, the results showed the attentional gradient effect (Iiidavas, 1990). Patients were more accu- rate to respond to stimuli located at 20° than 8°. Therefore, the results of the present study seem to suggest a functional dissociation of the mechanisms subserving attentional and gaze orienting and a differential role played by the frontal and parietal lobes in overt visual orienting.