Monocularly trained 11 adult split-brain cats with unilateral ablation of pretectum and/or superior colliculus in flux and form discriminations. When the midbrain lesions involved both colliculus and pretectum, there was a severe impairment in learning pattern discriminations using the eye on the lesion side. In those cases with the lesions chiefly in the colliculus or in pretectum, the deficit was present but less marked. When these same discriminations were taught before the midbrain lesion, no loss in retention was found postoperatively. (78 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)