UBC Theses and Dissertations
A neurobehavioral investigation of orienting behavior Midgley, Glenda C.
Models of the neural basis of visually guided behavior suggest that the mammalian brain has two independent visual systems: one involved in pattern vision, and the other involved in orienting to visual stimuli. Orienting was measured in this series of studies by examining both the thirsty rat's ability to disrupt licking in response to the presentation of visual and auditory displays and the animal's head and postural responses to the displays. Habituation of orienting behavior with repeated presentation of a display, and dishabituation to the subsequent introduction of changes in it were also examined. The effect on this behavior of variously sized cortical and subcortical lesions of the visual system and the influence of extrinsic and intrinsic variables were assessed. The investigation revealed that lesions of the superior colliculus do not result in visual agnosia or the inability to perform the appropriate motor responses involved in orienting; rather, while the orienting response is available in the behavioral repertoire of the lesioned animal, it is not always emitted in response to the visual displays that the intact animals treat as less salient. The superior colliculus lesioned animals do orient to and localize visual displays which are more salient for the intact animal. Further, the deficit in orienting to the "less" salient stimulus displays can be reduced or eliminated by changing the degree of water deprivation prior to testing and they are capable of using this display as a signal of shock. Lesions restricted to a very small portion of the lateral edges of the deep layers of the superior colliculus and the dorsal tegmentum had the same consequences as superior colliculus lesions, while lesions which included only the superficial layers of the superior colliculus did not. Lesions of the striate and extrastriate cortex did not significantly affect orienting behavior. Rats with lesions of the superficial or deep layers of the superior colliculus and rats with lesions including area 7 of cortex as well as the striate and extrastriate cortex, did,however, habituate more quickly than intact animals to the repeated presentation of the visual displays, and generally did not dishabituate in response to the changes in the visual displays. These findings suggest a relationship-between the cortex, the superficial layers, and the deep layers of the superior colliculus and the ability of animals to shift attention within a stimulus modality. The deep layers of the superior colliculus may also be important for shifts of attention between stimulus modalities (Jane, Levey, & Carlson, 1972). Overall, these results were discussed with regard to a possible modulating role of the superior-colliculus and cortex in orienting behavior and in terms of the parameters of orienting which must be taken into account in the development of an adequate model of the neural basis of orienting behavior.
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