The nature of residual vision in cats having undergone serial lesions of various visual structures was investigated behaviorally. Following the section of the left optic tract, learning performance on brightness and pattern discrimination was normal; the additional lesion of all the known visual cortical areas of the right hemisphere greatly impaired retention and learning of pattern discriminations. When a corpus callosotomy was further performed, a paradoxical improvement in both the retention and learning of a pattern discrimination was observed. This hemispheric disconnexion, by interrupting the abnormal influences exerted by the lesioned side on the intact deafferented hemisphere, improved visual functions mediated by the latter.