Color names, color categories, and color-cued visual search: sometimes, color perception is not categorical.

The relation between colors and their names is a classic case study for investigating the Sapir-Whorf hypothesis that categorical perception is imposed on perception by language. Here, we investigate the Sapir-Whorf prediction that visual search for a green target presented among blue distractors (or vice versa) should be faster than search for a green target presented among distractors of a different color of green (or for a blue target among different blue distractors). A. L. Gilbert, T. Regier, P. Kay, and R. B. Ivry (2006) reported that this Sapir-Whorf effect is restricted to the right visual field (RVF), because the major brain language centers are in the left cerebral hemisphere. We found no categorical effect at the Green-Blue color boundary and no categorical effect restricted to the RVF. Scaling of perceived color differences by Maximum Likelihood Difference Scaling (MLDS) also showed no categorical effect, including no effect specific to the RVF. Two models fit the data: a color difference model based on MLDS and a standard opponent-colors model of color discrimination based on the spectral sensitivities of the cones. Neither of these models nor any of our data suggested categorical perception of colors at the Green-Blue boundary, in either visual field.

Are discrimination thresholds a valid measure of variance for judgments of slant from texture?

There have been many experiments reported in the literature that have employed discrimination procedures to estimate the variance of observers' slant judgments from texture and binocular disparity, both individually and in combination. The research described in the present article identifies two serious methodological flaws in these studies. Although discrimination thresholds can be influenced by the variance of observers' slant estimates, they can also be affected by systematic biases in observers' judgments, and the presence of 2D cues that are irrelevant to the perception of slant. A series of five experiments is reported to show that: (1) the slants of surfaces specified by texture gradients can be systematically underestimated; (2) surfaces specified by texture gradients appear significantly less slanted than equivalent surfaces specified by binocular disparity; (3) the difference in bias between observers' slant judgments from stereo and texture may be more important than their relative variance in determining how these cues are weighted when presented in combination; (4) observers may be less sensitive to variations in apparent slant from texture than they are to variations in 2D cues that are unrelated to the perception of slant; and (5) these 2D cues may be the primary source of information for discriminating images of textured surfaces. These findings provide strong evidence that the results of prior discrimination studies have been misinterpreted because of the confounding effects of bias and/or 2D cues, and that this has resulted in several questionable conclusions that have been broadly accepted within the field.