Detection of visual stimuli in far periphery by rats: possible role of superior colliculus.

Previous work has been shown that rats with lesions of the superior colliculus fail to respond to distracting visual stimuli presented in the peripheral field while the animals are running towards a central stimulus. To assess how far this peripheral neglect is due to an attentional deficit, rats were trained before operation to obtain reward by running towards either peripheral or central lights that were presented when the animals' heads were stationary in a known position. Response to stimuli presented 120 deg from the midline was severely impaired after removal of the superior colliculus: the animals behaved as if they had difficulty in detecting the onset of the light. In contrast, response to stimuli 40 deg from midline was unaffected. Control lesions of striate cortex did not significantly impair performance at any position. The finding that collicular animals were impaired at responding to stimuli in the far periphery, that were not irrelevant distractors but instead predicted reward, suggests that one component of the visual neglect produced by damage to the superior colliculus in rats may be a sensory deficit in the far peripheral field. In addition, comparison with previous results indicates that training to attend to visual stimuli in more central regions does improve performance, as would be expected if the deficit were an attentional one. It is therefore argued that collicular neglect in rats should be regarded as a multicomponent impairment.