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Kentaro Miyamoto, Ikuya Murakami; Perceptual filling-in on a natural blind spot influences pupillary light reflex. Journal of Vision 2008;8(6):726. doi: 10.1167/8.6.726.
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Perceptual filling-in is induced when a light stimulus covers the retinal part (optic disk) corresponding to the blind spot. In this situation, the perceived surface seems to continue uniformly inside the blind spot and therefore the percept is larger than the area of actual stimulation confined outside the border. On the other hand, abrupt light stimulation causes reflexive contraction of the pupil, and the amount of reflex is known to change proportionately with light intensity. We aimed to see whether the pupillary light reflex in response to abrupt stimulus onset at the blind spot is based on the physical stimulation area or the perceived surface area as a result of filling-in.; A white disk stimulus twice as large as the blind spot of the right eye was displayed for 80 ms either on the blind spot or on its two adjacent areas. The amount of pupil contraction was measured. As a result, almost the same amounts of reflex were observed in all the conditions despite the fact that actual retinal stimulation is smaller (50% in area) when the stimulus was on the blind spot. Moreover, no reflex was observed when only the inside of the blind spot was illuminated. These results reveal that the perceived figural area formed through the process of perceptual filling-in affects pupillary light reflex. In a control condition, a white annular stimulus of the same size as the blind spot was displayed at the position exactly surrounding it. In parallel with pupil-size measurement, participants were requested to judge whether the stimulus shape was a completely filled disk or an incomplete one. Even though the annulus was indistinguishable from the disk, the amount of light reflex to the annulus was less than the reflex to the disk, suggesting involvement of some high-sensitivity mechanisms for light reflex.
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