Visual discrimination and spatial localization deficits after lesions of the tectofugal pathway in pigeons.

Abstract

21 White Carneaux pigeons (Columba livia)were trained on two identification tasks (intensity and pattern discriminations) and on two location tasks (right-left and four-key discriminations). Following training, lesions were placed in the optic tectum, or in nucleus rotundus or the nuclei isthmi, ascending and descending projections of the tectum, respectively. Large tectal lesions produced severe impairments on all tasks. The subjects were unable to relearn the identification tasks and, although able to relearn the location tasks, had great difficulty in locating the keys. The severity of deficits produced among subjects with lesions of nucleus rotundus depended on both lesion size and the extent to which the lesion infringed on the principal optic nucleus of the thalamus (OPT). Small rotundus lesions produced almost no impairment on any task. Larger lesions without OPT involvement produced impairment on identification tasks and differentially affected performance on location tasks. Large lesions of rotundus and OPT produced impairments on all tasks. The size of deficits produced among subjects with lesions of the nuclei isthmi were a function of the completeness of the lesion and did not depend on the extent of damage to other structures in the tectal core. Two control subjects showed unexpected impairment on the identification tasks which seemed to be related to damage to nucleus triangularis in the thalamus. Results of the research are compared with mammalian data.