Abstract
Categorical perception of color has conventionally been demonstrated as bringing advantage to the discrimination of equally spaced colors that belong to different lexical categories. The perceptual expansion of distance between categorically separable pairs and compression of that between categorically identical pairs have widely been demonstrated by quicker and more reliable detection of a unicolor image from lexically discrete backgrounds than term-sharing ones. Meanwhile, categorical effects that enhance performance in within-category condition have not been documented. The current study, however, found that comparing the degree of color contrasts inside two bicolor images is significantly faster and more accurate if the contrasting colors belonged to a single color term. This within-category advantage suggests that nondiscrete variation of hue inside one color category aids contrast judgment task while discrete lexical boundary impairs it. Consonant with the previous studies which document left-hemisphere dominance in categorical perception, the novel example of categorical effect was expressed only in the right visual field. Furthermore, significantly shorter reaction time was required for males than for females to make contrast judgment for a low contrast stimulus, but not for a high contrast target, suggesting possible gender difference in perceiving color contrast.