Factors Determining the Degree of Visual Defieit Following Ablation of the Inferotemporal Neocortex

Abstract

Based on instrumental conditioned avoidance responses, the effect of difficulty of visual task and that of the number of preoperative post-criterional trials as overtraining were studied on the degree of visual impairment following bilateral ablation of the neocortex in gyrus temporalis inferior and polus temporalis. Eleven dogs were trained on either a more difficult problem a or an easier problem β, concerning discrimination of flickering rate. Each dog was then given either 900 or 460 post-criterional trials as overtraining. Following bilateral inferotemporal ablation, the dogs were retrained to the criterional level on the same problem as before operation. The data obtained indicate that (1) the more difficult the discrimination tasks, the greater the relearning scores, (2) the greater the number of trials as overtraining, the less the relearning scores and (3) the visual performance of the preoperatively learned discrimination was not affected in the control dogs which received bilateral ablation of gyrus ectosylvius or unilateral removal of the inferotemporal lobe. It is obvious from the above findings that both factors, overtraining and difficulty of tasks, are important in evaluating the effect of ablation of the inferotemporal lobe on the visual deficit. We wish to thank Prof. K. Motokawa for his invaluable discussion and suggestion throughout the course of the experiment and the preparation of the manuscript.