Stimulus sampling and the use of distal visual cues in rats with lesions of the superior colliculus.

Rats with bilateral ablation of the superior colliculus (SC) were compared with sham-operated rats in two experiments. In the first, it was found that discrimination performance deteriorated as a function of S-R separation, to a similar extent in both groups. In this experiment, unlike earlier ones which found a deficit, the separation was introduced in a horizontal direction. In the second experiment, spatial orientation in the Morris Swimming Pool was found to be impaired in the SC rats both when the target platform was visible and when invisible. During their presence on the platform, these rats also engaged less often in upward orienting movements, although horizontal movements were of normal frequency. It is proposed (i) that there is an anisotropy in the SC's control of orienting head and eye movements in rats, and (ii) that the swimming pool deficit may be due to an impairment of ambient vision.