Effects of visual cortex lesions following recovery from monocular deprivation in the cat.

Six monocularly deprived (MD) and four normal cats were trained monocularly on two-choice form and pattern discriminations. MD cats trained through the initially deprived eye were able to learn the discriminations; however, they required many more trials than normals. Retention tests showed that MD cats have nearly perfect retention of the discriminations over periods of up to 4 months. With retention intervals of 6 months or longer, there is a tendency for the MD cats to show an initial drop in performance, particularly on more difficult discriminations. However, criterion performance typically was attained with considerable savings, indicating good retention even over these extended intervals. Following the preoperative training and retention testing, the cats received one of the three types of visual cortex lesions. Two MD cats received total visual cortex removal (areas 17, 18, and 19). This produced a complete postoperative loss of the discriminations with continued chance performance over 800--1000 trials. Two MD cats and two normal cats received removal of the monocular segment of area 17, with the central visual field projection region of area 17 and all of areas 18 and 19 remaining intact. This produced no loss of the discriminations in either normal or MD cats beyond what is expected on the basis of normal forgetting. Two MD cats and two normal cats received removal of areas 18, 19, and the central 5--10 deg. of the visual field projection in area 17. Postoperative retention was somewhat variable for both normal and MD cats. However, subsequent acquisition of the discriminations by both normal and MD cats was in sharp contrast to the prolonged deficits produced by total visual cortex lesions. These results indicate that one or more of visual cortical areas 17, 18, and 19 are involved in the recovery of visual discrimination capacities in MD cats. However, the monocular segment of striate cortex does not appear to be specially involved in this ability, as has been suggested by previous investigations. Possible mechanisms for the recovered visual capacities in MD cats are considered.