Visual orientation and detection following lesions of the superior colliculus in rats

Rats with bilateral lesions of the superior colliculus (SC) or with sham operations were trained on a modified version of the running task of Goodale and Murison (1975). The rats were required to shuttle between two large boxes, one of which required a choice between 5 doors, the other having only 1 door. A flashing distractor light at the side of a box was subsequently presented on once-daily test trials. For half the rats of each group these tests were given at 1 month and for the others at 3 months post-operatively. In agreement with previous studies, the SC-lesioned rats showed an abolition of orienting reactions to the distractor. (This was so in both boxes, i.e. a lower attentional load in the running task failed to alleviate the SC lesion-induced deficit.) However, only in the early-tested rats did the lesion cause a loss of freezing response to the distractor. Since in the late-tested group the rats froze but did not orient, it is suggested that the orienting loss at least in their case cannot be attributed to a partial visual field defect.