Medial versus lateral hyperstriatal lesions in pigeons: effects on autoshaping, non-matching-to-sample and spatial discrimination learning at short and long intertrial intervals.

Three experiments contrasted the effects of medial and lateral hyperstriatal lesions in pigeons. Expt. 1 found that both types of lesion obtained slower acquisition of autoshaping, compared to unoperated controls. No group differences in maintained rate of autoshaped responding were found. Expt. 2 found that lateral but not medial lesions disrupted choice performance in a non-matching-to-sample (NMTS) task, in which initial preference was for the correct stimulus; birds with lateral lesions responded more slowly to the sample stimulus than did birds with medial lesions. Expt. 3 found that medial but not lateral lesions disrupted both acquisition and reversal of a spatial discrimination at a long, but not at a short intertrial interval (ITI). Medial lesions damage primarily the hyperstriatum accessorium and lateral lesions, the hyperstriatum ventrale; but no significant correlations between the extent of damage to either of these structures and severity of behavioural disruption were obtained. Implications of these findings for theoretical accounts of hyperstriatal involvement in learning processes are discussed.