Visual discrimination defects in cats with temporal or occipital decortications.

Performance on visual discrimination problems by seven control (C) cats, eight cats with lesions in the posterior temporal (PT) cortex, and eight with destruction of the central 3 degrees-20 degrees of the retina's projection to the marginal (M) gyrus was investigated as a function of three variables: discriminanda (objects and patterns, type of pattern), learning requirement (acquisition, transfer, retention), and stimulus-response contingency (simultaneous, successive, concurrent discrimination). Group PT was impaired on 7/11 initial learning and transfer tests and on 0/3 retention tests, with pattern stimuli; it was inferior to Group C on 1/7 object discrimination tasks. No discrimination contingency was more likely than the others to reveal a significant deficit in Group PT. Group M was not impaired relative to Group C on any individual discrimination task. However, it made significantly more total errors on seven discriminations between complex patterns (embedded or masked figures) than Group C. On three discriminations between simple patterns (unmasked figures), Group M made fewer errors than Group C. This pattern of loss is qualitatively similar to, but milder than, that observed in previous cats with M lesions, very probably because the present M lesions were relatively small. The findings indicate that M and PT ablations produce differential impairments in cats, a selective difficulty in differentiating complex patterns after M lesions and a nonselective disruption of pattern discrimination learning after PT lesions.