Effects of pretectal lesions on rats wearing light-diffusing occluders.

The study provides behavioral evidence that the pretectal region of the subcortical visual system primarily mediates responses to diffuse rather than to patterned light stimuli: pretectal lesions induced greater transoperative deficits in performance of a light-dark discrimination task for rats wearing light-diffusing occluders than for non-occluded animals. Pretectal lesions also produced less transoperative disruption in animals trained to perform a pattern discrimination task (horizontal vs. vertical stripes). These results are precisely the opposite of those which follow ablation of visual cortex.