Abstract:

Categorical perception (CP) effect indicates that people are faster and more accurately at discriminating between two colors from different categories than two colors from the same category, even when between- and within-category chromatic separation sizes are equated. CP effect is an important evidence for the controversy between Sapir-Whorf hypothesis and the Universal Evolution theory (UE). The Sapir-Whorf hypothesis holds that CP is language-driven. They found that CP is left-lateralized and is disrupted by verbal, but not by nonverbal interference task. Moreover, the language-driven CP also got support from cross-language researches and neurophysiological studies. However, the Universal Evolution theory (UE) holds that CP effect results from universal focal colors and is independent from language. The current study presented three experiments that replicated and extended the earlier studies by using the same task but different participants. We compared green-blue discrimination of Chinese Naxi ethnic who speaks Naxi language and Chinese Han ethnic who speaks Mandarin. The two ethnics have different semantic boundaries of green-blue.

There are three experiments in the current study. In experiment 1, Participants were given a visual search task that required them to detect a single target color among 11 identical distracters. The stimuli were two colors G1 and G2 from green category (Munsell 7.5G and 7.5BG) and two colors B1 and B2 from blue category (Munsell 2.5BG and 2.5B). Four colors formed a graded series from green to blue, with the green-blue boundary falling between G2 and B1. In the visual search task, each stimulus display consisted of a ring of colored squares surrounding a central fixation marker. All squares were of the same color except the target. Participants were asked to press “F” or “J” key as soon and correctly as possible to indicate whether the target was in the left or right side of the circle. Experiment 2 was to ensure that the difference between the two groups in experiment 1 was not due to the slow reaction of the Naxi people to all colors. In experiment 3 block 1, participants were asked to finish green-blue visual search task and nonverbal interference task at the same time, and visual search task and verbal interference task in block 2.

Reaction time and accuracy of the visual search task showed that: 1) It was more difficult for the Naxi speakers, who always use the same word to express green and blue, to discriminate green and blue than the Mandarin speakers; 2) The categorical perception (CP) effect was found both in Naxi and Mandarin speakers. CP of Naxi speakers is probably related to their using similar-color objects to describe different colors in green-blue category; 3) The CP of Naxi and Mandarin speakers are both significant in the right visual field (RVF) and the left visual field (LVF). Moreover, the CP in the LVF was disrupted by the secondary task that engaged spatial working memory. Both the CP in the LVF and the CP in the RVF was disrupted by the verbal interference task. These results indicate that the CP in the LVF is related to the fact that Naxi and Mandarin language activates the right hemisphere.

All the findings reported here provide a more complex possible explanation of CP. Firstly, Naxi speakers were significantly more difficult to discriminate green and blue than Mandarin speakers. It supports the Sapir-Whorf hypothesis that language affects color perception. Secondly, CP appeared notably both in Naxi speakers and Mandarin speakers. It showed the online language effect on color perception, and supported universal category perception as well. Thirdly, CP was found both in the RVF and LVF. Moreover, CP in the LVF was disrupted by the pattern-memory task, and CP in the LVF and RVF were both disrupted by the verbal task. The results support the perspective combining the Universal Evolution theory (UE) and the Sapir-Whorf hypothesis.

Key words: categorical perception, bilateral effects, Sapir-Whorf hypothesis, Naxi speakers, Mandarin speakers.