Double dissociation of effects on learning of medial versus lateral hyperstriatal lesions in pigeons

Three experiments examined the effects of medial and lateral hyperstriatal lesions in two groups of pigeons. In Experiment 1, both hyperstriatal groups were impaired, relative to unoperated and operated control groups, in postoperative performance of preoperatively acquired serial reversal of both spatial and visual discriminations. The deficits of the two hyperstriatal groups appeared both quantitatively and qualitatively similar. Experiment 2 found that performance of spatial reversals was disrupted in the medial, but not in the lateral, hyperstriatal group by a long intertrial interval. Experiment 3 found that acquisition of simultaneous matching-to-sample was disrupted by lateral, but not by medial, hyperstriatal lesions; the lateral group also showed a lower rate of response to the sample stimulus than any of the other groups. Implications of these findings for current theories of hyperstriatal function are discussed.