Mandarin tone perception in Mandarin learners

Abstract

Mandarin tone perception is difficult for non-tonal language speakers. A fundamental issue in Mandarin learners is how well they are able to process lexical tones. To investigate the tone perception in Mandarin words, this research examined the effects of noise in native Mandarin speakers and Mandarin learners at acoustic and phonological/lexical levels through a behavioral study, and the neural mechanism underlying tone perception at phonological and lexical levels using an event-related potential (ERP) study.

In the behavioral study, the lexical tone perception ability was investigated in quiet and noise conditions, i.e., quiet, -15, -10, -5, and 0 dB signal-to-noise ratios (S/Ns). Performance was measured using a Mandarin Tone Identification Test at acoustic and phonological/lexical levels. There was a ceiling effect of performance across the four tones for both groups in quiet and at 0 dB S/N conditions. At -10 dB S/N, for both groups, tone 3 was found to be the easiest, tone 4 became the hardest, and tone 1/tone 3 was the easiest contrast to identify, suggesting a critical role of tone duration for tone processing in noise. The examination of accuracy and reaction time showed that noise could reduce tone perception performance by the two groups to a similar degree at not only the acoustic level but also the phonological/lexical level. However, it took Mandarin learners – but not native speakers – longer to identify correct tones at phonological/lexical level compared to when they were evaluated at -10 dB S/N, suggesting that non-native speakers use phonological/lexical cues in noise less efficiently than native speakers.

The difficulty of tone perception embedded in words for Mandarin learners may arise from any perceptual levels, acoustic, phonological or lexical levels. Therefore, ERP studies using mismatch negativity (MMN), phonological mapping negativity (PMN) and N400 were performed to evaluate processing of Mandarin tones at these perceptual levels, and to reveal the neural mechanisms underlying Mandarin tone perception. Results showed that MMN was significantly right hemisphere lateralized in Mandarin learners but symmetric in native speakers. This suggested that the processing of lexical tones at the phonological level has yet to fully develop in Mandarin learners. PMN was elicited using a picture-word matching task, and significantly elicited by the mismatch between the perceived lexical tones and expected lexical tones in native speakers, but not Mandarin learners. These results suggested that Mandarin learners mainly rely on acoustic processing for lexical tone perception but not phonological processing like native speakers. Although PMN was not elicited in tonal mismatch in Mandarin learners, N400 was elicited in the same condition, suggesting phonological processing and lexical processing could be dissociable in Mandarin learners. Evaluation of tone contrast discrimination ERP studies further supported these findings.

In sum, in unfavorable noise condition, we found that Mandarin learners performed worse than native Mandarin speakers on phonological/lexical tone perception. The neural mechanism leading to the difference between the two groups is likely to be that Mandarin learners mainly rely on general auditory processing whereas native speakers rely more on phonological processing for lexical tone perception.