Reversal learning in pigeons: effects of selective lesions of the Wulst.

The effects of bilateral lesions of individual laminae of the Wulst on reversal-learning performance in pigeons were evaluated. After surgery, the birds were trained to perform a simultaneous color discrimination. Once successful discrimination was achieved, the positive and negative stimuli were reversed, and the birds were again trained to criterion. Twenty such reversals were carried out. A multiple regression analysis indicated that those components of the Wulst that were critical for increasing the numbers of errors on each reversal were the laminae that receive the thalamofugal visual projections, that is, the nucleus intercalatus of the hyperstriatum accessorium and the hyperstriatum dorsale. Lesions in the other laminae of the Wulst (the hyperstriatum accessorium and the hyperstriatum intercalatus superior) had no effect on errors. There was no evidence of an increase in either perseverative errors or position habits in the birds with lesions, which suggested that the reversal deficits were not likely to be due to perseveration, attentional impairment, or inappropriate processing of spatial information. The deficit may have been produced by excessive interference between learning in a given session and learning in previous sessions.