The Effect of Inferotemporal Cortex Ablations on Eye Movements of Monkeys During Discrimination Training

Abstract

Two groups of monkeys, Grp. N, unoperated, and Grp. IT, with inferotemporal cortex ablations, were trained to view displays of the numerals ‘3’ and ‘8’ for the duration of a trial which ended in reinforcement for fixating the ‘8’ or non-reinforcement for the ‘3’. An adaptation of the Mackworth reflection eye movie camera apparatus recorded the location of visual fixations during a trial. Films of the first and fourth sessions of training were analyzed. Grp. N S's looked at the stimuli equally during Session 1 but by Session 4 had learned to preferentially observe the ‘8’. Grp. IT S's looked at the stimuli as frequently as Grp. N S'S but the ‘8’ and ‘3’ were observed equally often during both sessions. By Session 4 the strategies adopted by Grp. N (but not Grp. IT) were (a) increased lengths of fixation on the positive stimulus and (b) fewer shifts of the gaze off the total display. These results suggest that the mechanism disturbed by the inferotemporal cortex lesions involves central processing rather than observing behavior.