Delayed matching performance after visual Wulst lesions in pigeons.

Pigeons were trained preoperatively on a mixed delayed matching-to-sample (DMTS) task in which six different conditions were presented randomly; simultaneous matching, 0-, 1-, 2-, 4-, and 8-sec delays. Subjects that sustained extensive or complete damage to the visual Wulst and moderate damage to hyperstriatum ventrale showed a decrease in accuracy of performance to chance levels at all of the delay conditions as well as on simultaneous matching. After extensive retraining on the 0-sec-delay matching alone, performance on 0-sec-delay and simultaneous matching, presented in mixed DMTS, improved to between 70% and 90% correct. However, performance on delay conditions remained at chance level. All but one bird failed to show signs of postoperative improvement on delay problems in the course of the final testing. The data suggest that the conditional property of the task was a critical factor in the initial drop in accuracy on all of the presented problems. The relatively permanent loss of accuracy on all delay conditions is attributed mainly to the temporal separation of sample and comparison stimuli.