INTERHEMISPHERIC INHIBITION AND VISUAL PATTERN DETECTION

Abstract

Two experiments were performed in order to examine the quality of visual activity, specifically pattern detection in perimetrically intact hemivisual fields of hemiamblyopic individuals. The first experiment was directed at establishing a baseline of pattern detection performance for non-neurologically impaired individuals. Two developmentally distinct groups (5 old, 5 young) were tachistoscopically presented three shapes either left or right of a fixation spot in either the upper or lower visual quadrants. Threshold was evaluated by a modified method of limits technique, and defined as the minimum exposure duration needed for correct detection 66 percent of the time. Results obtained indicated that the age of the subject significantly affected pattern detection. Also, threshold attainment for all subjects was not affected by the visual field in which the stimulus was presented, but was affected by the quadrant position and size of the stimulus.;The second experiment examined the quality of form detection in intact hemivisual fields of hemiamblyopic individuals. Three groups (10 brain damaged hemivisually imparied, 10 brain damaged non-visually impaired, 5 old normals) were evaluated as in the first experiment. It was hypothesized that hemivisually impaired subjects would exhibit elevated thresholds for form detection in their intact hemivisual field as a result of interhemispheric inhibition. Results obtained indicated that the intact hemivisual fields of hemiamblyopic subjects exhibited significantly elevated thresholds for form detection as compared to results obtained for all other groups. It was demonstrated that brain damage without visual impairment does not significantly elevate threshold above the performance for the established age norms of older normal subjects. Further, as demonstrated in the first experiment, the quadrant position as well as stimulus size, independent of group examined, significantly elevate threshold above the performance for the established age norms of older normal subjects. Further, as demonstrated in the first experiment, the quadrant position as well as stimulus size, independent of group examined, significantly affected form detection. Based on these results, it was concluded that a decrease in sensitivity for form detection exists in the visual field ipsilateral to the damaged hemisphere. It was proposed that the decrease in sensitivity resulted due to unilateral lesions involving visual mechanisms, exerting interhemispheric modality specific inhibition.