Hemispheric differences in the discrimination of line orientation

Normal, right-handed subjects trained to discriminate between rectangles oriented with their major axis along the vertical, the horizontal and the two intermediate directions, and presented to the right or left side of a fixation point, exhibited faster discriminative reactions (pressing of a key) to stimuli appearing in the right visual field. By contrast, two other groups of normal, right-handed subjects performing a similar reaction-time task with stimuli oriented along other directions (respectively, 30° and 45° from the vertical to the right and the left; 15°, 30°, 45° and 60° from the vertical) were faster in discriminating stimuli presented in the left visual field. These differences in performance for the two halves of the visual field are attributed to hemispheric differences in the discrimination of line orientation. The opposite hemispheric superiorities found with the different discriminations are in turn attributed to the use of verbal mediators in the discrimination preferred by the left hemisphere, and by the use of a non-verbal strategy in the discriminations preferred by the right hemisphere. © 1974.