Posterior Cortical Atrophy: The role of simultanagnosia in deficits of face perception
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Date
2012-03-21
Authors
Locheed, Keri
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Abstract
When viewing a face, healthy individuals tend to fixate on upper regions, particularly the eyes,
which provide important configural information about the spatial layout of the face. In contrast,
individuals with face blindness (prosopagnosia) rely more on local features – particularly the
mouth. Presented here is an examination of face perception deficits in individuals with Posterior
Cortical Atrophy (PCA). PCA is a rare progressive neurodegenerative disorder that is
characterized by atrophy in occipito-parietal and occipito-temporal areas. PCA primarily affects
higher visual processing, while memory, reasoning, and insight remain relatively intact.
Common among individuals with PCA is simultanagnosia, an inability to perceive more than one
object or detail simultaneously. One might consider simultanagnosia the most extreme form of a
feature-based approach. In a series of investigations, individuals with PCA and their healthy
control participants completed a same/different discrimination task in which images of faces
were presented as cue-target pairs. Eye-tracking equipment (Experiment 1) and the newly
developed Viewing window paradigm (Experiment 2) were used to investigate scanning patterns
when faces were presented in full view, and through a restricted viewing aperture, respectively.
In contrast to previous prosopagnosia research, individuals with PCA each produced unique scan
paths that focused on one aspect of the face. Individuals with PCA tended to focus on areas of
high-contrast but many of these areas were not diagnostically useful, suggesting that they were
having difficulty processing the face even at a featural level. These results suggest a role of
simultanagnosia in the scan patterns of PCA patients that is not reflective of ‘typical’
prosopagnosia, and instead points to simultanagnosia, sometimes matched with basic perceptual
impairments, as a significant contributor to the face perception deficits seen in PCA.
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Keywords
posterior cortical atrophy, simultanagnosia, face perception