Categorical representation of visual stimuli in the primate prefrontal and inferior temporal cortices

The 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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Brain and Cognitive Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Freedman, David J. (David Jordan), 1975-

Advisor dc:contributor.advisor

• Earl K. Miller.

• Brain and Cognitive Sciences.

Statement dc:rights

• M.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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8352

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8352