Perception of Tones for Mandarin Speakers: Evidence from Behavioral and Brain fMRI Experiments

105

The dissertation presents two studies on the perception of fundamental frequency (F0) contours of Mandarin tones by native speakers of Mandarin Chinese. One study measures the subjects’ behavioral responses, including latency and accuracy, and the other uses functional magnetic resonance imaging (fMRI) methodology to investigate the association of specific brain regions with the perception of Mandarin tones. The behavioral study adopted a 2x2x2 factorial design to investigate the effects of linguistic context (sinewave pitches vs. lexical tones), and F0 contour contrasts (familiar vs. unfamiliar) on the performance of discrimination tasks (auditory vs. category) in a same/different paradigm. The present study observed that F0 contours of Mandarin tones are not perceived the same by the native listeners of Mandarin in the speech (i.e., lexical tone) vs. non-speech context (i.e., sinewave pitches) when the effects of task types and familiarity with F0 contour contrasts are taken into account. The subjects performed better in sinewave pitches than in lexical tones in two conditions: (1) in the category discrimination of familiar contour contrasts, and (2) in the auditory (non-categorical) discrimination of unfamiliar contour contrasts, while in the other conditions, the perception of sinewave pitches and lexical tones did not show significant difference. These results imply that the perception of F0 contours of Mandarin tones is a function of task, familiarity, and speech context. The brain fMRI experiment investigated the association of Mandarin fundamental frequency (F0) contour perception with the superior temporal gyrus (STG) and the inferior frontal gyrus (IFG) when tones were input from the right ear. Adopted in this study are two types of auditory stimuli: sinewave pitches (SW) and lexical tones (LX). LX refers to tones with, and SW, tones without, vocalic information. The brain fMRI experiment observed that LX perception, compared with SW perception, had additional activations at the left IFG and more noticeable activations at the right IFG. The additional activations at the left IFG imply association with the perception of vocalic information of LX. Despite the differences, SW and LX perception shared common activations at the left STG and the right IFG, suggesting that vocalic information plays no key role in tonal perception. The involvement of the left STG supports the phonemic feature of Mandarin tones. The present investigation reveals that solely the left STG of the brain cannot achieve the processing of Mandarin tones, and the role of the right IFG cannot be ignored.