Single neurons in several cortical areas in monkeys update visual information in conjunction with eye movements. This remapping of stimulus representations is thought to contribute to spatial constancy. The central hypothesis here is that spatial updating also occurs in humans and that it can be visualized with functional MRI.
In Chapter 2, we describe experiments in which we tested the role of human parietal cortex in spatial updating. We scanned subjects during a task that involved remapping of visual signals across hemifields. This task is directly analogous to the single-step saccade task used to test spatial updating in monkeys. We observed an initial response in the hemisphere contralateral to the visual stimulus, followed by a remapped response in the hemisphere ipsilateral to the stimulus. Our results demonstrate that updating of visual information occurs in human parietal cortex and can be visualized with fMRI.
The experiments in Chapter 2 show that updated visual responses have a characteristic latency and response shape. Chapter 3 describes a statistical model for estimating these parameters. The method is based on a nonlinear, fully Bayesian, hierarchical model that decomposes the fMRI time series data into baseline, smooth drift, activation signal, and noise. This chapter shows that this model performs well relative to commonly-used general linear models.
In Chapter 4, we use the statistical method described in Chapter 3 to test for the presence of spatial updating activity in human extrastriate visual cortex. We identified the borders of several retinotopically defined visual areas in the occipital lobe. We then tested for spatial updating using the single step saccade task. We found a roughly monotonic relationship between the strength of updating activity and position in the visual area hierarchy. We observed the strongest responses in area V4, and the weakest response in V1. We conclude that updating is not restricted to brain regions involved primarily in attention and the generation of eye movements, but rather, is present in occipital lobe visual areas as well.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-12052005-001608 |
| Date | 20 March 2006 |
| Creators | Merriam, Elisha P. |
| Contributors | Marlene Behrmann, Ph.D., Mark D'Esposito, M.D., Christopher R. Genovese, Ph.D., Carl R. Olson, Ph.D., Seong-Gi Kim, Ph.D., Carol L. Colby, Ph.D. |
| 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-12052005-001608/ |
| 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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