Cerebral Control of Voluntary Visual Attention, Directed with Or Without Orienting Saccades (Hemispatial Neglect, Right Hemisphere).

The objective of this dissertation was to clarify the contributions made by the frontal and parietal lobes to mechanisms of voluntary visual attention and orientation. 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) in two reaction time tasks that measured a subject's ability to shift attention to a stimulus with or without moving the eyes to it. Each used a symbolic, spatial cue (arrow) that either indicated the location of a visual target (valid cue) or did not (invalid cue). In Experiment I the subjects closed a manual switch in response to a stimulus while maintaining central fixation. In Experiment II they made a saccade to the stimulus. A significant difference in reaction time to the targets following the valid and invalid cues was used to assess the process of directed visual attention. The left frontal patients responded more slowly in Experiment I to the right visual field target than the left visual field target, suggesting that this region is necessary for maintaining a normal level of visual receptivity and /or manual responsivity to contralateral targets. Right parietal males and right frontal females showed an overall elevation in manual reaction time, reflecting an inability to maintain a normal level of overall visual receptivity and /or manual responsivity. Right frontal males and right parietal females showed no effect of cue validity in Experiment I, reflecting a deficit in covert, directed visual attention (i.e., made without observable orienting movements). These results indicated a double dissociation of function within the right hemisphere that differed between the sexes. In addition, the right frontal males and right parietal females showed an abnormal effect of cue validity on saccade amplitude (Exp. II). The nature of this saccade dysmetria differed depending on the lesion locus in the right hemisphere, suggesting that the frontal and parietal lobes contribute different functions to the process of selecting visual targets. Members of each sex may on the average use different strategies for target selection.PhDPsychobiologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161292/1/8702799.pd