Effects of unilateral thalamic lesion upon interocular transfer of visual discrimination in pigeons. I. Lesion in the trained hemisphere (memory access deficits).

Two groups of pigeons received a unilateral thalamic lesion in the hemisphere contralateral to the eye used for monocular training of a line orientation discrimination. The first group was trained monocularly on the discrimination after the lesion, and the second group received the lesion after the birds were successfully trained on the discrimination task. Then both groups were trained on the same task with their previously untrained eye to examine interocular transfer of discrimination. Lesion in the nucleus rotundus before monocular discrimination retarded acquisition of the original monocular learning but did not cause deficits in interocular transfer, whereas the rotundal lesion after the monocular discrimination learning resulted in deficits in interocular transfer. These results suggest (1) the bird could learn monocular discrimination with the hemisphere ipsilateral to the viewing eye when the contralateral hemisphere was not accessable, and (2) the bird learned monocular discrimination with the hemisphere contralateral to the viewing eye when both hemispheres were intact. Lesion in OPT did not cause deficits in interocular transfer. This result suggests a crucial role of the tecto-fugal pathway in interocular transfer.