Visual intensity and pattern discrimination deficits after lesions of ectostriatum in pigeons^†

Eighteen pigeons were trained to discriminate between visual stimuli that differed in either intensity or pattern. Bilateral, electrolytic lesions were made in ectostriatum or the lateral neostriatum. Pigeons with ectostriatum lesions had severe post-operative performance deficits. The magnitude of the deficit and the amount of post-operative retraining necessary to restore the birds to pre-operative performance levels varied directly with the amount of bilateral destruction of ectostriatum. Pigeons with little or no involvement of ectostriatum showed little or no change in discrimination performance post-operatively. Similarities between morphological and functional organization of the reptilian, avian and mammalian visual systems are discussed.