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Patricia Winkler, Kyle C. McDermott, Gideon Caplovitz, Michael Webster; Figural Chasers. Journal of Vision 2011;11(11):1014. doi: https://doi.org/10.1167/11.11.1014.
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In the lilac chaser illusion (Jeremy Hinton, en.wikipedia.org/wiki/Lilac_chaser), splotches of color in the periphery fade to invisibility so that the negative afterimage when each splotch is removed becomes the most conspicuous feature. The illusion provides a compelling illustration of adaptation processes in color vision and how they influence color salience. We explored spatial variants of the illusion to test for comparable effects of adaptation on the salience of visual form. Stimuli consisted of a central image corresponding to a spatial norm (analogous to gray) surrounded by peripheral images that were spatially distorted (analogous to color contrast). The norms and distortions included geometric figures (circle vs. ellipses), edges and texture (focused vs. blurred or sharpened images), and faces (normal vs. configurally distorted), with each distorted figure briefly and sequentially replaced with the norm. Observers fixated the center image and then rated the appearance of the steady-state distorted images or the undistorted transient relative to the norm. For each, moderately distorted images in the periphery tended to take on the appearance of the central figure, while the physically matched transient appeared as a strong spatial aftereffect (e.g. so that the physical ellipses appeared more circular while the circle appeared as an ellipse with the opposite orientation). These percepts are consistent with an adaptation effect that renormalizes the appearance of the peripheral distortion so that it appears more neutral, but may also include an effect of foveal capture on the appearance of peripheral stimuli. The analogous aftereffects for color and form suggest that “Troxler-like” fading in the periphery may occur for many stimulus dimensions and that these adaptation effects may generally enhance the salience of novel stimuli by discounting responses to the prevailing stimulus.
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