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dc.contributor.advisorEarl K. Miller.en_US
dc.contributor.authorFreedman, David J. (David Jordan), 1975-en_US
dc.contributor.otherMassachusetts Institute of Technology. Dept. of Brain and Cognitive Sciences.en_US
dc.date.accessioned2005-08-23T19:24:24Z
dc.date.available2005-08-23T19:24:24Z
dc.date.copyright2002en_US
dc.date.issued2002en_US
dc.identifier.urihttp://hdl.handle.net/1721.1/8352
dc.descriptionThesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2002.en_US
dc.descriptionIncludes bibliographical references.en_US
dc.description.abstractThe ability to group stimuli into meaningful categories is a fundamental cognitive process though little is known its neuronal basis. To address this issue, we trained monkeys to perform a categorization task in which they classified visual stimuli into well defined categories that were separated by a "category-boundary". We recorded from neurons in the prefrontal (PFC) and inferior temporal (ITC) cortices during task performance. This allowed the neuronal representation of category membership and stimulus shape to be independently examined. In the first experiment, monkeys were trained to classify the set of morphed stimuli into two categories, "cats" and "dogs". Recordings from the PFC of two monkeys revealed a large population of categorically tuned neurons. Their activity made sharp distinctions between categories, even for stimuli that were visually similar but from different classes. Likewise, these neurons responded similarly to stimuli from the same category even if they were visually dissimilar from one another. In the second experiment, one of the monkeys used in the first experiment was retrained to classify the same stimuli into three new categories. PFC recordings collected after the monkeys were retrained revealed that the population of neurons reflected the three new categories but not the previous (now irrelevant) two categories. In the third experiment, we recorded from neurons in the ITC while a monkey performed the two-category "cat" vs. "dog" task. There were several differences between ITC and PFC neuronal properties. Firstly, a greater proportion of ITC neurons were only stimulus selective but not category tuned.en_US
dc.description.abstract(cont.) Secondly, while many PFC neurons displayed category tuning that persisted into the memory delay, such tuning in the ITC was primarily observed during stimulus presentation. Thirdly, whereas many PFC neurons reflected the monkeys' decisions about whether a stimulus indicated a behavioral response, most ITC neurons conveyed information about the visual stimuli only, and not about the monkey's task-related decisions. In conclusion, our results suggest that neurons in the PFC and ITC can convey information about the category of visual stimuli. The differences in neuronal responses between the ITC and PFC support the hypothesis that the ITC plays an important role in object recognition and visual learning while the PFC is more involved in cognitive functions related to executive control.en_US
dc.description.statementofresponsibilityby David J. Freedman.en_US
dc.format.extent130 leavesen_US
dc.format.extent9288319 bytes
dc.format.extent9288077 bytes
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/pdf
dc.language.isoengen_US
dc.publisherMassachusetts Institute of Technologyen_US
dc.rightsM.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.en_US
dc.rights.urihttp://dspace.mit.edu/handle/1721.1/7582
dc.subjectBrain and Cognitive Sciences.en_US
dc.titleCategorical representation of visual stimuli in the primate prefrontal and inferior temporal corticesen_US
dc.typeThesisen_US
dc.description.degreePh.D.en_US
dc.contributor.departmentMassachusetts Institute of Technology. Dept. of Brain and Cognitive Sciences.en_US
dc.identifier.oclc50544119en_US


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