Abstract: It has been well documented that color perception exhibits the characteristics of categorical perception such that participants’ performance is better when discriminating stimuli across color category boundaries than within the same color category. However, it is unclear whether the effect of categorical perception on color perception is in fact a perceptual phenomenon. Most of the evidence for the categorical perception of color was derived from tasks that considerably involved working memory; therefore, it is possible that the categorical effect results from the involvement of verbal labeling in working memory rather than being a pure perceptual phenomenon. Thus, it is important to provide tests that separate the perceptual process from verbal memory. The present study extended the research of Franklin (2005) and Gilbert et al. (2006) by incorporating the two experimental paradigms and aimed to identify whether categorical perception of color occurs in the perceptual stage of the task.
A 2 (interference tasks: no interference vs. verbal interference) × 2 (color stimuli: within category vs. between categories) × 2 (visual field: left visual field vs. right visual field) within-subject design was implemented in the present study. Eighteen participants (19~22 years old) were tested. First, each participant’s blue–green lexical boundary was determined. Subsequently, they were required to perform a target detection task. Each stimulus display consisted of one color square on a different background color. The color square was randomly presented on one of the 12 locations around the fixation point. The participants were required to respond to the stimulus by pressing one of the two keys after detecting whether the color square appeared on the left-hand side or the right-hand side of the stimulus display.
The result indicated that the reaction times in the between categories condition were much faster than those in the within category condition; this suggested that categorical perception does affect color perception. Moreover, this effect was unaffected by the verbal-interference task. Further, for both the left and right visual fields, there were significant effects of categorical perception; however, there was no significant difference in the magnitude of the effect between left and right visual fields.
These results suggest that the categorical perception of color occurs during the perceptual stage. Meanwhile, since the effect of categorical perception on color perception was found in both the left and right visual fields and the difference between the effects was not at a significant level, the results are consistent with the notion that there is no significant difference between the left and right hemispheres on color perception.

Key words: categorical perception, language label, compression effect, expansion effect