Effects of unilateral temporal lobe removals in man on tachistoscopic recognition in the left and right visual fields

Abstract

Thirteen patients with right temporal lobe removals, ten with left temporal lobe removals, and forty-four normal subjects were compared on tachistoscopic recognition in the left and right visual fields. Result and conclusions were as follows: 1. (1) When a group of four letters was presented in either the left field or the right in random succession, both operated groups were impaired relative to the normal subjects in both visual fields; furthermore, each operated group tended to show a relatively greater impairment in the field contralateral to the removal. The severity of the recognition loss was found to be unrelated to the presence or severity of upper quadrantic visual field defects. The results are interpreted as supporting the view that extrageniculo-striate mechanisms within both right and left temporal lobes facilitate visual perception, and that each makes its contribution to vision by interacting mainly with the visual system of the same hemisphere. 2. (2) When two groups of four letters were presented simultaneously (with one in the left field and one in the right), the right temporal group again showed impairment in both visual fields, but the left temporal group now showed impairment only on the right. A second difference in the effects of left and right temporal removals was revealed by a correlational analysis: under conditions of succesive presentation, the left temporal group showed a nearly perfect correlation between recognition in the two fields, whereas the right temporal group showed a non-significant correlation. An attempt was made to relate these differences in the effects of left and right temporal removals to previous findings of “dominance” of the right temporal lobe for visual perception. 3. (3) One aspect of perceptual performance which was not affected by the removals was the gradient of recognition for the several letter positions within a field. These gradients were found to differ between the two fields for the normal subjects and patients alike, and it was suggested that the differential gradients might account for the overall differences in recognition between left and right field which have previously been reported for normal subjects.