Contribution of striate inputs to the visuospatial functions of parieto-preoccipital cortex in monkeys.

In Experiments 1 and 2, monkeys received 3-stage operations intended to serially disconnect parieto-preoccipital from striate cortex. At each stage (unilateral parieto-preoccipital removal, contralateral striate removal and posterior callosal transection) the monkeys were tested for retention of the landmark task, a visuospatial discrimination sensitive to the effects of bilateral parieto-preoccipital damage. To check the effectiveness of the disconnection, the monkeys were also tested after removal of the remaining parieto-preoccipital cortex. The results demonstrated that corticocortical inputs from striate cortex are crucial for the visuospatial functions of parieto-preoccipital cortex, just as they had been shown earlier to be crucial for the pattern discrimination functions of inferior temporal cortex. Relative to inferior temporal cortex, however, parieto-preoccipital cortex was found to be especially dependent on ipsilateral (as compared with contralateral) striate inputs. In Experiment 3, monkeys received bilateral lesions of either lateral on medial striate cortex and were tested on both a pattern discrimination task, to assess residual inferior temporal function, and the landmark task, to assess residual parieto-preoccipital function. The results indicated that the pattern discrimination functions of inferior temporal cortex are especially dependent on inputs from lateral striate cortex, whereas the visuospatial functions of parieto-preoccipital cortex are equally dependent on inputs from lateral and medial striate cortex. The relatively greater contribution to parieto-preoccipital than to inferior temporal cortex made by ipsilateral and medial striate inputs (representing contralateral and peripheral visual fields, respectively) can also be seen in the receptive field properties of parieto-preoccipital and inferior temporal neurons. The differences in the organization of striate inputs to these two cortical association areas presumably reflect differences in the processing required for spatial vs object vision.