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Eye region processing : insights from acquired prosopagnosia

University of British Columbia

Face processing models propose a holistic representation of faces in the human brain. Additionally, behavioral studies in healthy individuals indicate a bias towards the eye region of faces, namely a Feature Salience Hierarchy. The exact mechanisms of this feature salience hierarchy are not known. Using behavioral face perception and neuroimaging experiments, we investigated the perceptual mechanisms and the neural correlates of the feature salience hierarchy, and the correlations of the human perceptual performance with the neural signal. Prosopagnosia studies also indicate an asymmetrical loss of the ability to deduce information from the eye region of faces. In a cohort of ten acquired prosopagnosia patients, we investigated and characterized the relationship between the structural brain damage and the behavioral face processing impairments. This dissertation examines the perceptual and neuroanatomical bases of the bias towards the eye region of a face in healthy individuals and the deviation from this bias in relation to the brain lesion locations in acquired prosopagnosia patients. Our findings confirm the dominance of the eyes in feature salience hierarchy in an adaptation aftereffects experiment. Investigation of the neuroanatomical correlates of the feature salience hierarchy shows that the activation pattern in Fusiform Face Area (FFA) correlates with the human perceptual performance, suggesting FFA’s involvement in the feature salience hierarchy demonstrated for the eye region of faces behaviorally. Examination of the eye region processing in prosopagnosia patients shows that both apperceptive and associative variants of prosopagnosia can cause eye region processing deficits, yet apperceptive prosopagnosia patients with inferior occipitotemporal cortex lesions have significantly more severe deficits in eye region processing. Face scanning patterns in a learning and memory task with unlimited viewing times demonstrate that both healthy and prosopagnosic individuals spend more time looking at the upper halves of faces while learning the faces, yet prosopagnosia patients spend significantly longer durations studying the faces. Our investigation of memory for half faces indicate that when presented in isolation, the upper and lower face halves do not have different contributions to face memory in healthy subjects. Prosopagnosia patients are similarly impaired in memory for upper and lower face halves.

Text

2014-08-07

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/49942

Neuroscience

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/