Abstract
Recent reports have suggested that lesions of the superior colliculus may impair the orienting or scanning movements of the head that are thought to serve a key function in visual discrimination. In the present investigation computer-video “actograms” were used to quantify the head movements of freely moving hamsters performing a simultaneous visual discrimination. Hamsters with collicular lesions did not differ from the controls in their head movement spectra, but there was a significant reduction in the incidence of the pauses in locomotion during which these movements are made. Intact animals showed slower and irregular progression interspersed with pauses during which they made scanning movements, whereas collicular hamsters made straighter runs. Although the rate of learning of lesioned hamsters was not impaired, our data strongly suggest that they used different orienting and learning strategies. When tested for the effects of novel stimuli, unrelated to the task, normal hamsters reacted strongly with active exploratory scanning movements, but collicular animals did not, although qualitative changes in their behaviour suggested that the novel stimuli were not being ignored.
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