CEREBRAL CONTROL OF DIRECTED VISUAL ATTENTION AND ORIENTING SACCADES

Abstract

The object of this experiment was to identify the contribution of the frontal and parietal lobes to the control of visual attention and volutary saccades. A symbolic spatial cue (arrow) was used to indicate validly or invalidly the location of a visual target located to the left or right of the cue. Manual reaction time and reaction time to initiate a saccade to the target were measured. Patients with damage to the left frontal lobe (n = 6), right frontal lobe (n = 7) and right parietal lobe (n = 7) were compared with normal control subjects (n = 20). A sex difference was found for the right cerebral hemisphere patients in the manual reaction time data. Right parietal males and right frontal females showed an overall elevation in manual reaction time, reflecting an inability to maintain a normal level of visual arousal and/or motor activation. Conversely, right frontal males and right parietal females were not influenced significantly by cue validity, suggesting that they were unable to direct visual attention in a covert manner. All subjects showed a normal effect of cue validity on saccade reaction time. Thus the cortical areas studied do not appear to be necessary for directing visual attention with a saccade. Cue validity, however, affected saccade amplitude, especially in the left visual field of patients with right hemisphere damage. The cue validity effect depended both on the sex of the subject and the anterior/posterior location of damage in the right hemisphere. Damage to the right frontal lobe resulted in an ‘under’ reaction to the spatial cues, especially in the male patients. Saccades were smaller than normal following the valid cues, but larger than normal following the invalid cues. The effect was opposite following damage to the right parietal lobe. In this case, saccade amplitude reflected an ‘over’ reaction to the spatial cues, especially in the female patients. Saccades were larger than normal following valid cues and smaller than normal following invalid cues.