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Sae Kaneko, Stuart Anstis; Contours can inhibit flash-enhanced simultaneous contrast. Journal of Vision 2013;13(15):T16. doi: 10.1167/13.15.16.
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A gray test disk looks apparently brighter on a black surround, and apparently darker on a white surround (simultaneous contrast). We have found (Kaneko & Murakami, 2012) that this simultaneous contrast is greatly enhanced by flashing the stimulus up only briefly (“flash-enhanced contrast”). We now report a new effect of an outline circle that suppresses this flash-enhanced contrast.
If the preceding or following uniform gray field presents an outline circle, congruent with the test disk, this disk now shows virtually no flashed contrast, but appears to remain mid-gray. Even an Ehrenstein subjective circle, made from several radii occluded by an ‘invisible’ disk, could reduce the flashed contrast. We have two theories: 1, ‘Disk Longevity’: the visual system takes the outline circle as a continuation of the gray disk over time, thus effectively increasing its duration. 2, ‘Masking’ : the outline circle masks or hides the existence of the gray disk. The real outline circle also reduces the visibility of the disk, although the reduction is not perfect and subjects can still detect the disk location very accurately. However an Ehrenstein circle has little or no effect on disk visibility. Therefore we believe that simple masking cannot explain the reduced flashed contrast. We propose that without the circles present, the visual system constructs a light or dark disk from the light/dark edge information available during the brief flash. The real or Ehrenstein circle interferes with this construction process.
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