Orienting behavior by rats with visual cortical and subcortical lesions.

The effect of visual cortical and subcortical lesions on orienting behavior was assessed bu examining the rats' ability to interrupt an ongoing response and perform appropriate head and postural adjustments to repeatedly presented auditory or apparently moving visual stimuli. Large lesions of the entire superior colliculus (SC) or the deep layers of the SC did not result in visual agnosia or the inability to perform the motor responses involved in orienting. Rather, the orienting response simply ws not emitted to visual stimuli that the intact rat treated as less salient, but was to those it treated as more salient. Lesions of either the superficial layers of the SC or visual cortex also did not completely prevent orienting to very salient, apparently moving visual stimuli, but did produce changes in the number of responses made to such stimuli and in the occurrence of other components of orienting behavior. It was suggested that the SC and visual cortex play a modulatory role in orienting behavior and that stimulus characteristics must be considered in the development of neuronal models of orienting behavior.