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Abstract:
Abstract: A critical element of visual perception and object
recognition is the brain's capacity to reconstruct contours not
physically present in the visual image itself. One method of
investigating these processes has involved the use of illusory
contour (IC) stimuli (e.g. Kanizsa, 1979). The processing of IC
stimuli has been extensively studied in animals with the general
finding that a population of cells in area V2 is highly sensitive
to such contours, as to a lesser extent are some cells in V1. It
would appear that the ability to respond to such illusory
boundaries is present at the earliest stages of cortical processing
and these findings seem to infer a bottom-up process that is
hard-wired into the earliest stages of the visual system. However,
human ERP studies have reported relatively late (>180ms)
effects, suggesting that this is a later higher-order effect. The
present study addressed this apparent discrepancy between the
animal and human literature. We recorded ERPs (64-channels) to IC
stimuli from 22 subjects. IC stimuli began to be processed
differently relative to control non-IC stimuli, at just 90-100ms as
evidenced by modulation during the falling phase of the visual P1
component over occipito-temporal scalp. Further, scalp current
density maps also suggest early involvement of parieto-occipital
cortices in IC processing.
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