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Bhavin R. Sheth, Shinsuke Shimojo; Color and orientation pop-outs differentially affect discrimination. Journal of Vision 2001;1(3):115. doi: 10.1167/1.3.115.
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Visual properties such as orientation, color and luminance are functionally similar in that each of them individually provide a basis for perceptual pop-out (Treisman & Gelade, 1980). Pop-outs are commonly believed to facilitate information processing in a variety of tasks such as detection (Bravo & Nakayama, 1992) and discrimination. Here, we show a special case in which all pop-outs do not facilitate discrimination. A 3 × 3 matrix of (vertically or horizontally) oriented grating patches is shown (followed by a matrix of plaid masks) either in the periphery (10 deg. eccentricity, 1 × 1 deg. area each, 180–300 ms duration) or in the fovea (0.5 × 0.5 deg. area each, 5 ms duration). The observer (n=5 throughout) discriminates the central target's color or orientation. If the target is a unique color, discrimination improves compared to a control in which all items are of the same color. Conversely, if the target's orientation is salient, discrimination does not improve but deteriorates compared to a no-orientation pop-out control. If luminance is substituted for color, the effect is similar. There are no attentional differences between conditions. Color does not pop out more than orientation. Phenomenologically, the data show real differences between so-called elementary visual properties (Nothdurft, 1993; Wolfe et al., 1993). Though counterintuitive, a greater degree of suppression by an orthogonally oriented surround as compared to an iso-oriented one and relatively little suppression of a uniquely colored stimulus by the surround can explain the data. This poses new challenges for physiology and computation (Fitzpatrick, 2000).
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