Shankar, Sunita2006-07-282006-07-2820002000http://hdl.handle.net/10012/576In a set of four experiments this study set out to replicate and extend the findings of Sun, Carey, & Goodale (1992) of the use of time-to-collision (t-t-c) in a visually guided task in Mongolian gerbils, and then investigated the effects of lesions to different cortical areas. In the first three experiments gerbils were trained to run in the dark toward a target on a computer screen. On some trials, the target changed in size as the animal ran toward it in such a way as to produce "virtual targets" that appeared closer than or farther away from the real target, if the animals were using t-t-c information. In Experiment 1, it was confirmed that gerbils use time-t-contact information to modulate their speed of running toward a target, but the results show that it is not the only source of information used. Experiment 2 established a cortical role in the use of time-to-collision as it was established that visual cortex lesions attenuate the ability of lesioned animals to use information from the visual target to guide their run. Control frontal cortex lesioned animals were able to use t-t-c information to modulate their deceleration, but their runs were different from those of shams. Experiment 3, showed that small radio frequency lesions, of either the primary visual cortex, or the lateral extrastriate regions of the visual cortex also affected the use of t-t-c. It is possible that the animals in Experiment 1 and the sham animals in Experiment 2 detected the target as moving in some trials, and the differences between sham and frontal lesioned animals seen in Experiment 2 may be reflected deficits in processing this object motion by the frontal lesioned animals. This hypothesis was tested with a changed protocol in Experiment 4, and while some trends in the predicted direction were seen, the results were not convincing enough to confirm the role that frontal and lateral extrastriate areas play in the processing of object motion, as compared to the processing of t-t-c information.application/pdf4349178 bytesapplication/pdfenCopyright: 2000, Shankar, Sunita. All rights reserved.Harvested from Collections CanadaDoctoral Thesis