Acquisition of visual discrimination after nucleus rotundus lesions in pigeons

Abstract

Lesions of nucleus rotundus thalami of pigeons result in severe losses in the postoperative retention of visual intensity and pattern discriminations. The present experiment was an investigation of the effects of such lesions on postoperative acquisition. Five pigeons were pretrained to peck stimulus discs and obtain grain reward from a dispenser. Following this pretraining, bilateral lesions were made in nucleus rotundus. After recovery from surgery, the birds were given their first exposure to the stimuli. The performance of these birds was compared with the preoperative performance in the same discrimination task of 27 pigeons that were being trained concurrently in another experiment. The results indicate that nucleus rotundus lesions impair original learning as well as retention of established discrimination performances. Several possible explanations of the nature of the deficit are discussed.