Date of Award

9-2003

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Supervisor

Professor D. Maurer

Abstract

I examined the role of early visual experience in the development of expert face processing by comparing individuals with normal visual histories to patients deprived of early visual experience because of congenital cataract. The patients were tested following treatment, and after several years of visual experience (at least 8 years), on three tasks that measured different aspects of face processing.

The first task measured face discrimination based on sensitivity to second-order relations (the spacing among facial features), and sensitivity to featural information (the shape of the features). The patients performed normally at discriminating faces based on featural processing, but were severely impaired at discriminating faces based on second-order relational processing (gluing the features into a gestalt). Unlike normal controls, the patients showed no evidence of encoding faces holistically. The third task measured face detection based on sensitivity to the first-order relations (i.e., two eyes above a nose and mouth): classifying two-tone Mooney stimuli as either face-like or not. The patients were as fast and accurate as normal controls at detecting Mooney faces.

Because the right hemisphere plays an important role in face processing, I also used Task 1 to test patients who were treated for early visual deprivation that affected mainly the left hemisphere or right hemisphere. Deprivation affecting mainly the right hemisphere cause impairment in second-order relational processing that was as severe as deprivation affecting both hemispheres. Deprivation affecting mainly the left hemisphere had no apparent effects on face processing.

Together these findings indicate that the normal development of certain aspects of face processing require visual experience during infancy. Early visual input to the right hemisphere may be especially important for setting up the neural circuitry that will become responsible for expert face processing.

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