Impairments of Visual Object Transforms in Monkeys

Monkeys were first trained on a series of standard, unchanging visual objects to obtain food reward. After reaching criterion on each subject, training with it continued but on 20 per cent of the trials the object was transformed in (1) size, (2) orientation, or in (3) its shadow configuration. Monkeys with lesions either of the inferotemporal cortex or the foveal prestriate region were impaired in identifying all three types of transforms as the rewarded object. They were also slightly impaired in continuing postcriterion high levels of performance on the nontransformed objects, but it was shown that the transform deficit was still present when this factor was partialled out. The groups with transform deficits were also impaired initially in their discrimination between solid cones of varying apical angle, although their final performance approached that of controls. The inferotemporal group, especially with the lesion placed anteriorly, had a deficit in their initial learning of the untransformed objects as well as in the retention of a preoperatively learned pattern discrimination; they were also deficient in selecting food objects from among an array of nonfood objects. No deficits were seen in animals with lesions of the parietal lobe or the fundus of the superior temporal sulcus in any task. The results and other relevant animal evidence are interpreted in terms of the view that the anterior temporal lobe is concerned with the storage of an object-centred prototype, necessary in turn for the attachment of positive or negative meaning, and the more posterior inferotemporal lesions with the addressing of view-centred visual information en route to the anterior regions. They are also consistent with the findings on the recognition of 'unusual views' made by Warrington and coworkers in patients with posterior lesions.