Lexical tones have presented great difficulties for second language learners whose native language is non-tonal. A number of recent studies suggest categorical-like perception of lexical tones by native Mandarin speakers. Can native speakers of non-tonal languages acquire categorical representations of lexical tones? Are there any differences between L1 and L2 tone perceptions? This study investigates brain responses to lexical tone categorization for three groups of adult listeners: 1) native English speakers who had no exposure to Mandarin before age 17, but took advanced Mandarin courses as adults; 2) naive English speakers; and 3) native Mandarin speakers. Two tonal continua were derived from natural speech through interpolation within two tonal contrasts (Tone 1/Tone 4; Tone 2/Tone 3). Firstly, category boundaries were examined through classic identification and discrimination tasks. Secondly, high-density electroencephalography (EEG) was used to record brain responses while participants listened to tones in two oddball paradigms: across-category and within-category. If perception of lexical tones is categorical, cross-category deviants are expected to elicit larger ERP responses (specifically, mismatch negativity (MMN) and P300) than within-category deviants. Both behavioral and ERP results indicate that lexical tones are perceived categorically by native Chinese speakers but not by inexperienced English speakers. Although English learners of Chinese demonstrated categorical perception in behavioral tasks, their ERP response did not differ between within- and across-category conditions, however, significantly greater P300 responses were observed. Acoustic cues and characteristics of L2 phonological learning in adulthood are discussed.
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