Goldfish were trained to perform visual intensity and pattern discriminations. Three groups of fish had bilateral ablation of the caudal optic tectum, a fourth consisted of unoperated controls and a fifth group consisted of sham-operated controls. The fish were tested after various postoperative intervals ranging from 19 to 147 days. The lesions produced modest deficits in intensity discrimination irrespective of postoperative interval. The fish that began training on the pattern discrimination after 14-18 postoperative days showed no improvement in performance. Fish that began training after 39 postoperative days showed improvements in performance after about 65 postoperative days. The group that began training 158-160 postoperative days showed steady and persistent improvements in discrimination performance. The results suggest that improvements in pattern vision after partial tectal ablation follow the same time course as compression of the retinotectal map after partial ablation of the tectum.