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Richard N Aslin, Robert A Jacobs, Peter W Battaglia; Depth-dependent contrast gain-control. Journal of Vision 2003;3(9):49. doi: 10.1167/3.9.49.
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© ARVO (1962-2015); The Authors (2016-present)
The brain has evolved mechanisms of adaptive contrast gain-control to compensate for variations in retinal contrast (or receptor sensitivity) that are present despite a uniform stimulus contrast. Retinally localized increments or decrements in contrast undergo rapid adaptation, resulting in contrast constancy across the visual field. We extend this contrast adaptation to the third dimension by introducing a retinally localized decrement in contrast that is present only in a near or far depth plane. Subjects fixated a small cross that moved smoothly across a sine wave grating (2 c/d, 60% contrast). The grating was viewed stereoscopically and depicted a near and a far surface, side-by-side, containing disparity, texture, and perspective cues, with a sharp depth gradient in between. A patch of the grating (2-D Gaussian, 3 deg diameter), located 7 deg below the fixation cross, contained a region of contrast decrement (from 60% to 0%). This region of contrast decrement was present only when the fixation cross was on the near or the far surface. Thus, if that region of the retina underwent depth-dependent contrast adaptation, contrast gain should increase after extended viewing, but only for the depth surface that was adapted. Subjects were adapted for 3 min as the fixation cross oscillated across both the near and far surfaces. A contrast matching task assessed contrast adaptation at the near surface and at the far surface, with the standard Gabor patch located 7 deg above the fixation cross and the comparison Gabor patch located 7 deg below the fixation cross, coincident with the location of the Gaussian contrast decrement. Results indicated that contrast gain increased for the adapted retinal location, but only for test trials presented at the near (or far) surface that contained the contrast decrement. These results suggest that contrast gain-control has an adaptive mechanism that is sensitive to and conditioned upon the depth of the adapted surface.
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