Effects of inferotemporal cortex lesions on form-from-motion discrimination in monkeys

The inferotemporal cortex of primates plays a prominent role in the learning and retention of visual form discriminations. In this experiment we investigated the role of inferotemporal (IT) cortex in the discrimination of two-dimensional forms defined by motion cues. Six monkeys were trained to a criterion level of performance on two form-from-motion problems. Three of these animals received complete bilateral lesions of IT cortex, while the other three served as unoperated controls. All animals were then retrained to criterion to evaluate the effects of IT lesions on the retention of form-from-motion learning. Compared with the control group, the lesion group was significantly impaired on both problems. Following retention testing, we trained both groups of monkeys on two new form-from-motion problems to investigate the effects of IT lesions on acquisition rates for new learning. The lesion group performed well on the new problems; the learning rates of the operated and control groups were not significantly different. When forms were defined by luminance cues, monkeys with IT lesions, like those in previous studies, were impaired both for retention and for acquisition. These findings indicate that the anterograde effects of IT lesions on learning new form discriminations are less severe for forms defined by motion cues than for forms defined by luminance cues. However, the retrograde effects of IT lesions on retention are severe for forms defined by either cue.