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Leedia A. Svec, Thomas Reiner, Michael A. Webster; Chromatic contrast and neural adjustments to blur. Journal of Vision 2002;2(7):140. doi: 10.1167/2.7.140.
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© ARVO (1962-2015); The Authors (2016-present)
The perceived focus of a luminance-varying image can be strongly affected by prior adaptation to blurred or sharpened images or by simultaneous contrast from blurred or sharpened surrounds. We examined whether comparable adjustments occur for patterns defined by chromatic contrast, for which spatial resolution is inherently lower. Stimuli included natural images, filtered noise, and simple edges that were varied either in luminance contrast, or in LvsM or SvsLM chromatic contrast. The image spectra were filtered by multiplying the original amplitude at each frequency (f) by f to power n, with n varied from −1 to +1 in small increments to form an array of images ranging from moderately blurred to sharpened. A 2AFC (“too blurred” vs. “too sharp”) staircase was used to vary the presented image in order to find the image that appeared best focused. Measurements were made before or after 3 minutes adaptation to blurred or sharpened images, or in the presence of blurred or sharpened surrounds formed by 8 adjacent images from the same array. Prior adaptation shifted the perceived focus of all patterns. For example, blurred adapting edges caused a test edge to appear sharper, or vice versa. These effects were selective for the color or luminance variations defining the pattern, but were weaker for color compared to luminance. Weak and color-selective spatial induction of blur also occurred for LvsM patterns, while little induction was observed from SvsLM surrounds. Moreover, blurred luminance surrounds could “capture” chromatic edges, causing physically focused color edges to appear blurred, even though the same surrounds caused a luminance test edge to appear sharper. Thus luminance surrounds had opposite effects on luminance and chromatic edges. These asymmetries suggest that the neural processes regulating blur perception may qualitatively differ for luminance and chromatic contrast.
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