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Teresa Schubert, David Rothlein, Trevor Brothers, Kerry LeDoux, Barry Gordon, Michael McCloskey; High-level visual processing despite lack of awareness: Evidence from event-related potentials in a case of selective metamorphopsia. Journal of Vision 2013;13(9):1106. doi: 10.1167/13.9.1106.
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© ARVO (1962-2015); The Authors (2016-present)
We report a patient, RFS, with a category-specific metamorphopsia for Arabic digits. MRI shows parietal atrophy; concurrent motor and memory deficits support a diagnosis of cortico-basal degeneration. RFS’s recognition, writing, and mental imagery of Arabic digits are dramatically impaired, yet semantic knowledge of number quantities is intact. Digit forms are perceived as grossly distorted and the digits distort other stimuli (e.g., faces or words) in the spatial or temporal vicinity, rendering RFS unaware of their identity or form. For example, RFS cannot report whether a stimulus embedded in a large 8 is an intact or scrambled face. We probed whether stimuli embedded in digits are processed despite RFS’s inability to perceive them. Results from three event-related potential (ERP) experiments indicate that the identity of stimuli embedded in large digits are processed despite RFS’s distorted perceptual experience. First, faces embedded in digits elicited a reliable N170 response (relative to scrambled faces), indicating visual processing sufficient to distinguish faces from scrambled faces. Second, target words embedded in digits elicited a reliable P300 response (relative to non-target words). Finally, a reliable N400 response was elicited in response to incongruency between an auditory word and a written word embedded in a digit. These findings support the hypothesis that word stimuli presented over digits are processed to the level of amodal lexical representations without conscious awareness. The results are consistent with theories of conscious awareness which posit obligatory feedback/recurrent processing underlying coherent visual percepts.
Meeting abstract presented at VSS 2013
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