Recent experiments in neurophysiology have begun to examine the active nature of our perceptual experience. One area of research focuses on the impact of eye movements on visual perception. With each eye movement, a new image is presented to the brain, yet our perception is that the world remains stable. This phenomenon, termed spatial constancy, depends on a convergence of information about our eye movements with sensory information from the visual system. Neurons in the lateral intraparietal cortex (LIP) contribute to the construction of an internal representation of space that is updated or remapped with each eye movement.
Although the basic phenomenon of remapping has been described, many questions remain unanswered. Here we describe two experiments designed to gain a greater understanding of spatial updating in the primate brain. First, we hypothesized that spatial updating would be equally robust throughout the visual field. We tested this by monitoring the activity of neurons in LIP while varying the direction over which a stimulus trace must be updated. We found that individual neurons remap stimulus traces in multiple directions, though the strength of the remapped response is variable. Across the population of LIP neurons, remapping is effectively independent of saccade direction. These findings indicate that the activity of LIP neurons can contribute to the maintenance of spatial constancy throughout the visual field.
Second, to begin to understand the circuitry underlying remapping, we studied a special case: when a stimulus must be updated from one visual hemifield to the other. We hypothesized that the forebrain commissures provide the primary route for this across-hemifield remapping. We tested this by comparing the signal related to within- and across-hemifield remapping. We predicted that in split-brain monkeys, across-hemifield remapping would be abolished while within-hemifield remapping would remain robust. Surprisingly, we found that in split-brain monkeys, LIP neurons can remap stimulus traces across hemifields, though this signal is weaker than that associated with within-hemifield remapping. This finding implies that while the forebrain commissures are likely to be the primary route for the interhemispheric transfer of visual information, they are not the only route available. This indicates that a distributed network of brain regions supports spatial updating.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-11082004-172529 |
| Date | 31 January 2005 |
| Creators | Heiser, Laura Madeline |
| Contributors | Daniel Simons, Carol Colby, Tai Sing Lee, Carl Olson, Anthony Grace, Tatiana Pasternak |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-11082004-172529/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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