CCN talk June 7, 2016

Michael McCloskey

Department of Cognitive Science, Krieger School of Arts and Sciences at Johns Hopkins

Title: Category-Specific Impairment of Visual Awareness

Time: 4:00-5:00

Place: Moore Hall, Room 202

Abstract

I describe a remarkable impairment of visual perception and its implications for understanding visual awareness. RFS, a 61-year old geologist with cortical atrophy, is selectively impaired in perceiving and comprehending digits (e.g., 5, 8): When shown a digit, he reports seeing an uninterpretable jumble of contours ("like spaghetti"), and is unable to identify or copy the digit. In contrast RFS is intact in perceiving and comprehending word numbers (e.g., seven) and Roman numerals, and his mathematical skills are excellent when tested without digits. RFS is also intact in perceiving and identifying most letter and other symbols (e.g., #), although he reports some perceptual distortion for certain letters. Digits, in addition to being misperceived themselves, distort RFS's perception of other visual stimuli in the spatial or temporal vicinity. For example, RFS was entirely unable to identify pictures enclosed within digits, but was 100% correct when the enclosing characters were letters. In two ERP studies RFS viewed faces and words enclosed within digits. These stimuli gave rise to normal electrophysiological responses (N170 for faces, P300 for words), despite RFS's complete lack of awareness for either the faces or the words. I suggest that RFS's impairment involves disordered feedback from domain-specific recognition processes to earlier levels of representation. Finally, I consider the implications of this account for understanding relationships between perceptual recognition and perceptual awareness.

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