Kathleen Hall

This dissertation examines how Mandarin-dominant Mandarin-English bilinguals use post-stop fundamental frequency (F0) in the production and perception of the stop voicing contrast in Mandarin and English. Their use of post-stop F0 is then compared with that of native English speakers. Additionally, the influence of cognitive load on the use of post-stop F0 is investigated. Along with cross-linguistic differences in the use of post-stop F0, this work foregrounds variability within participants and explores the production-perception interface on an individual level. A corpus study and a set of parallel online production and perception experiments were devised. The results from the corpus study indicated that post-stop F0 following aspirated stops was lower than that following unaspirated stops in Mandarin. However, the data from the production experiment, in which the bilinguals read aloud words typifying the voicing contrast in stops, suggested the opposite pattern in both Mandarin and English. Furthermore, the post-stop F0 difference in English was larger as compared to Mandarin, indicating that more production weight was assigned to post-stop F0 in English than in Mandarin. The data from the perception experiment, which featured a forced-choice task, showed that the bilinguals used post-stop F0 as a cue in perceiving stops in both English and Mandarin, with higher post-stop F0 leading to more aspirated/voiceless responses, but they allocated more weight to post-stop F0 when the audio stimuli were presented as English words than as Mandarin words. When the bilinguals' post-stop F0 weights for English were compared with those of native English speakers, however, an asymmetry was revealed: even though both groups shared similar production weights, English listeners still had a higher perceptual weight than the bilinguals. With respect to cognitive load, which was induced by a concurrent visual search task, it seemed to introduce more variability to the perceptual weights, but only for English listeners. Overall, these results argue for a dual function of F0 in cueing phonological voicing in stops and tones across modalities in Mandarin. Furthermore, they suggest a dynamic nature of the post-stop F0 cue, which adapts to different language contexts, though this adaptability is constrained by the first language.

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This dissertation compares the lexical tone perception abilities of two populations with different bilingual configurations: Cantonese-dominant adults who grew up in Hong Kong (referred to as homeland speakers), and English-dominant adults who grew up in a Cantonese-speaking household in Canada (heritage speakers). From infancy both were exposed to Cantonese as a first language in terms of chronological order; however, after the onset of schooling, each became dominant in the majority language of their respective society. Given this background, this study investigates whether heritage speakers' perception of lexical tones of a non-dominant first language (Cantonese) exhibits cross-language effects from a dominant second language (English) that does not have a contrastive dimension of tone. A series of perception experiments was conducted using the word identification paradigm. Eight types of audio stimuli were presented to homeland and heritage speakers (N=34 per group), each of which represented a specific configuration of four variables: whether the acoustic signal contained segmental and tonal information, whether the target word was isolated or embedded in a carrier sentence with semantic context, and whether the meaning of the target word was congruous with the carrier sentence. In each trial, participants saw pictures of the target word and minimally contrastive tonal competitors, and were instructed to choose the picture that represented what they heard.Major findings of this study were: (1) among the eight stimulus types, the accuracy gap between the two groups was the biggest when the stimuli were low-pass-filtered monosyllables with no segmental information or semantic context, which suggests that homeland speakers have a significantly greater ability to identify tonally contrastive words by solely relying on tonal information. (2) Both groups showed confusion of overlapping subsets of tone pairs, but heritage speakers had a higher error percentage, which indicates a quantitative but not qualitative difference between the two groups. (3) When the target word was semantically incongruous with the carrier sentence, homeland speakers outperformed heritage speakers by attending to acoustic information, while heritage speakers relied on semantic information relatively more often. In other words, the two groups used different listening strategies in tone identification.

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