Abstract: Speech perception focuses on the mapping between properties of the acoustic signals and linguistic elements such as phonemes. One of the most important features of speech perception is the phenomenon known as categorical perception (CP) that the continuous sensory inputs are coded categorically. CP has an important influence on the developmental time course of speech perception. Although a large amount of research on CP has been conducted in English and other languages, CP (especially its developmental course) in Chinese has been barely studied. Chinese is a tonal language with some specific phonetic characteristics, such as strong aspiration with long positive voice onset time (VOT) and lexical tones characterized by syllable-level f0 contours. However, the questions such as whether the perception of VOT and lexical tones in Chinese is categorical and how they develop with age are still unaddressed. Using the stimuli of VOT and tone continua created by Klatt, the present two studies investigated CP of VOT and lexical tones in Chinese and their developmental course.
Using the classical identification and discrimination paradigm, study 1 investigated the perception of Chinese lexical tone continua and VOT continua in adults. The study was comprised of 4 experiments which included identification and discrimination of VOT and tone respectively. Stimuli were presented to 20 adult subjects in each experiment. The results demonstrated that the perceptions of VOT and lexical tones are both categorical for Chinese adults.
Study 2 further investigated the developmental course of Chinese phonetic categorization across lexical tone and VOT continua. The experimental design of this study is a 2 (entity stimuli: VOT, lexical tone) by 4 (age: 5ys, 6ys, 7ys, adults) mixed experiment design. The former was a within-subject factor, while the latter was a between-subject one. Results from Study 2 revealed that six-year-old children already acquired adult-like lexical tone CP competence, but even 7-year-old children were not as good as adults when doing CP of VOT tasks. Therefore, it is proposed that CP of lexical tones is acquired earlier than CP of VOT in Chinese. Further analysis of the correlation between the 2 phonological characteristics showed that they are not correlated with each other. Thus, it is suggested that these two phonetic characteristics are distinct and go through different developmental courses. CP of lexical tone seems to be a phonetic characteristic that is easier to acquire than CP of VOT in Chinese.
In conclusion, the findings demonstrated that: (1) the perceptions of both VOT and lexical tones in Chinese are typically categorical for adults; (2) there are different developmental courses for CP of lexical tones and VOT in Chinese. According to the theory proposed by Burnham, we conclude that the Chinese lexical tone is a “robust” contrast and is categorically perceived in early childhood; in contrast, VOT is a “fragile” contrast that requires more time to develop.

Key words: Category Perception, Voice Onset Time (VOT), lexical tones, developmental course