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Michael McCloskey, Teresa Schubert, David Rothlein, Brenda Rapp, Jason Brandt, Xi Sheng; Feedback from Domain-Specific Visual Recognition Processes: Evidence from Selective Digit Metamorphopsia. Journal of Vision 2012;12(9):434. doi: 10.1167/12.9.434.
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© ARVO (1962-2015); The Authors (2016-present)
RFS, a 61-year-old geologist with cortical atrophy that may reflect early-stage cortico-basal degeneration, is selectively impaired in perceiving and comprehending the Arabic digits 2-9. Presented with a digit in this range, he reports seeing an uninterpretable jumble of contours ("like spaghetti"), and is unable to identify, copy, or even trace the digit. In contrast RFS is intact in processing the digits 0 and 1. Furthermore, he accurately perceives and comprehends number words (e.g., seven) and Roman numerals, and his mathematical skills are excellent when tested without Arabic numerals. Processing is also intact for most letters and other symbols (e.g., #), although RFS reports mild perceptual distortion for a subset of letters (M, N, R, S, Z). Remarkably, the digits 2-9 are not only misperceived, but also 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, or overlaid by, digits in the 2-9 range, but was 100% correct when the enclosing or overlaying characters were 0s, 1s, or letters. The digits 2-9 also impaired identification of subsequent stimuli. A pre-mask of digits or # symbols was presented for 2 s, followed after a variable ISI by a target letter. RFS was severely impaired in identifying the letter at ISIs of 1 s or less, but only when the pre-mask consisted of digits in the 2-9 range. We interpret RFS's impairment in terms of feedback from domain-specific recognition processes. We propose that in RFS a malfunctioning digit-recognition process not only fails to identify digits in the range 2-9, but also sends disordered--and disruptive--feedback to earlier perceptual levels of representation. Finally, we suggest that phenomena from other domains can be explained in similar terms (e.g., selective prosopometamorphopsias in which faces appear flattened, melted, or otherwise distorted).
Meeting abstract presented at VSS 2012
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