Sixty albino rats with unilaterallesions of striate cortex, unilateral orbital enucleations, or sham operations were trained on black-white and horizontal-vertical discriminations, with order of problem presentation counterbalanced. Mastery of the initially acquired discrimination greatly enhanced acquisition of the second; however, the previously reported enhancement of acquisition associated with unilateral striate ablation proved to be of limited generality: it occurred only during initiallearning of the horizontal-vertical problem.

No abstract

In the wake of several studies that have cast doubt upon the effectiveness of contact eye covers in restricting vision, we performed a series of five experiments to the end of achieving reversible blinding of the albino rat. The data of Experiment 1 indicated that the contact eye cover can be as effective as a rubber cup in restricting visual input. In Experiment 2, animals that were fitted binocularly with opaque eye covers performed as if blind on a task involving acquisition of pattern discrimination. In Experiment 3, binocular coverage with the opaque eye cover resulted in chance performance across 300 trials of a previously acquired pattern-discrimination habit. In Experiment 4, the base diameter of the eye cover was found to be a critical factor: Performance of a previously acquired brightness discrimination was reduced to chance levels by contact eye covers that approximated 7.0 mm in diameter. In Experiment 5, a smaller eye cover (6·mm diam) had no effect in limiting the visually evoked electrocortical response of the albino rat, while an eye cover of 7.2-mm diam produced a reliable attenuation of the response. The collective results indicate that appropriately fabricated contact eye covers are a viable means of restricting visual input and may justifiably be considered contactoccluders.

Small, unilateral cortical lesions were placed in either medial-anterior, lateral-anterior, or posterior cortex of 20 male, Sprague-Dawley, albino rats. In addition, unilateral sham operations were performed on 8 rats from the same stock. All subjects had been trained prior to surgery with diametrically opposed visual habits mediated by opposite cerebral hemispheres. The opposing habits were, insofar as possible, evenly matched prior to surgery. After surgery, lesioned hemispheres, regardless of locus of lesion, were slower in acquiring the habit they mediated, than were unlesioned hemispheres. Further, unlesioned hemispheres dominated in test trials in which subjects chose one of the two cue doors with both eyes open. These findings confirm that the "interocularly conflicting discrimination" baseline detects a role of extrastriate cortex in mediation of pattern discrimination habits. They further indicated that losses occur without regard to the various locations of lesion employed.

6 albino rats were trained under appetitive motivation to perform diametrically opposed visual discriminations of pattern via opposite eyes. Small lesions were subsequently placed unilaterally in anterior neocortex. Following a period of post-surgical recovery, subjects were re-trained on the diammetrically opposed discriminations in alternating 10-trial blocks. Every subject made more post-surgical errors on the discrimination mediated by the eye contralateral to the lesion. Since albino rats have virtually complete decussation of the visual system, this indicates selective impairment in mediation of performance of pattern discrimination in the part of the lesioned hemispheres. Thus, findings previously obtained in studies involving aversive motivation are general to appetitively motivated tasks.