Effects of lesions of the optic tectum on the ability of turtles to locate food stimuli.

In a previous experiment, it was demonstrated that the removal of portions of the optic tectum in a turtle, Podocnemis unifilis, impaired its ability to perform a horizontal vs. vertical line discrimination task. To further elucidate the nature of this deficit, turtles (P. unifilis) were operantly conditioned to locate a food object at varying positions in an aquarium. Preoperatively, all of the animals approach a food object in a direct manner. Animals with a bilateral lesion of the optic tectum approach the food object in an indirect manner. One animal, with a unilateral lesion approached the food object in both an indirect and a direct manner depending on the position of the object in the visual field.