On-going Projects
Evidential value of voice quality acoustics in forensic voice comparison
Project summary
The task of forensic voice comparison typically involves the comparison of a known voice of the suspect with an unknown voice of the offender. In cases which involve speech recordings (e.g. hoax calls, ransom demands, threatening voice message, conversation with an accomplice), the comparison of voices can help the trier-of-fact (e.g. judge/jury) or investigating authorities (e.g. police) decide whether the two voices were produced by the same speaker or different individuals. A major goal of forensic voice comparison research is to identify features in speech which are useful for distinguishing voices. Voice quality (e.g. breathy/creaky/hoarse/nasalised voice) analysis by phoneticians has been reported to be useful for characterising speakers and widely conducted in forensic casework, but voice quality as forensic evidence has mostly been assessed subjectively by experts and reported in terms of categorical auditory labels. Across different fields of forensic comparison sciences, there has been increasing pressure from regulating bodies (e.g. US National Research Council and UK Law Commission) for forensic experts to shift from relying on subjective judgments to the quantitative assessment of the strength of the evidence using the likelihood ratio framework. This project explores the quantitative aspects of voice quality and involves likelihood-ratio analyses of voice quality acoustics in a bid to determine their evidential value. How voice quality acoustics may complement other speech features in speaker discrimination will also be examined.
Funding
- Early Career Scheme, Hong Kong Research Grants Council. (PI: Ricky Chan, HKD 450,000)
Interim outputs
- Chan, R. (2023). Evidential Value of Voice Quality Acoustics in Forensic Voice Comparison. Forensic Science International, 348, 111725.
- Chan, R. (2023). Speaker discriminatory power of voice quality acoustics under forensic conditions. Proceedings of the 20th International Congress of Phonetic Sciences. Prague, Czech Republic.
Why are lexical tones difficult to learn? Insights from incidental learning of tone-segment connections
Project summary
Tone languages (e.g. Cantonese, Mandarin, Thai) employ contrastive pitch patterns (i.e. lexical tones) to distinguish word meaning. Why L2 lexical tones are difficult to acquire, especially for learners with non-tone L1, has been a long-standing issue for researchers, language teachers and learners alike. While L2 sounds present different kinds of challenges to learners at the phonetic, phonological, and lexical levels, previous studies on L2 tone learning mostly focused on the phonetic level (e.g. L2 tone discrimination/identification), and and a few on the lexical level. However, the ability to perceive or discriminate different L2 tones explicitly does not entail the ability to encode pitch patterns as abstract tone categories at the syllable level, which is the pre-requisite of using abstract tone categories as lexical cues.
The project mainly investigates the role of 1) L1 prosodic system; 2) musical training; and 3) proficiency in a tone language on the forming novel abstract syllable-level tone categories (phonological level), via the incidental learning (i.e. without intention) of tone-segment mappings.
Funding
- Faculty of Arts and Social Sciences Research Fund, Lancaster University. (PI: Ricky Chan, GBP£2200)
- Small Project Funding, HKU. (PI: Janny Leung; Co-I: Ricky Chan, HKD 72,800)
Interim outputs
- Chan, R. & Leung, J. (2020). Why are lexical tones difficult to learn? Insights from the incidental learning of tone-segment connections. Studies in Second Language Acquisition, 42(1), 33-59.
- Chan, R. (2019). Difficulty in learning L2 tones: Insights from the incidental learning of tone-segment mappings. Proceedings of the 17th International Congress of Phonetic Sciences. Melbourne, Australia.
Tonal parameters for forensic speaker comparison
Project summary
This project examines speaker variability in the production of lexical tones and its implications for forensic voice comparison. Based on spectral and statistical analyses of controlled production data, it has been demonstrated that the dynamic contours of Cantonese and Mandarin citation tones and co-articulated tones exhibit significantly greater between-speaker variation than within-speaker variation across different speaking rates, tonal contexts, and voice levels. Further analysis reveals that tone inventory density has a clear effect on the degree of variation in tone coarticulation, potentially attributable to speakers’ effort to maintain perceptual contrast. The findings demonstrate that lexical tones may provide useful parameters for forensic voice comparison.
A further study explores the speaker-discriminatory performance of various approaches to tonal f0 parameterisation. Findings suggest that modelling surface tone f0 generally yields better results than modelling the underlying articulatory mechanism of tone production.
Funding
- Doris Zimmern HKU-Cambridge Hughes Hall Scholarships. (Ricky Chan, GBP 89,237)
- Cambridge Overseas Trust, University of Cambridge. (Ricky Chan, GBP 17,000)
- Fieldwork Funding, University of Cambridge. (Ricky Chan, GBP 5,700)
- The International Association for Forensic Phonetics and Acoustics (IAFPA) Research Grants. (Ricky Chan, GBP1,250)
Interim outputs
- Chan, R. & Wang, B. X. (submitted). Modelling lexical tones for speaker discrimination.
- Chan, R. (accepted). Tone languages. In F. Nolan, K. McDougall & T. Hudson (Eds), Oxford Handbook of Forensic Phonetics. Oxford University Press.
- Chan, R. (2020). Speaker discrimination: citation tones vs. coarticulated tones. Speech Communication, 117, 38-50.
- Chan, R. (2016). Speaker variability in the realization of lexical tones. International Journal of Speech, Language and the Law, 23(2), 195-214.
- Chan, R. (2015). Speaker variability in the production of coarticulated Tones. Proceedings of the 16th International Congress of Phonetic Sciences. Glasgow, UK.
Justice in China: Showing the way with forensic voice comparison
Project summary
Legal justice hinges on the quality of the forensic evaluation of evidence. This is
particularly true for forensic voice comparison (FVC) in China, where the scientific bases of methods and procedures are limited. A recent survey revealed a number of serious issues, notably 1) the lack of empirical validation of features analysed by FVC
practitioners; 2) potential overestimation of the strength of voice evidence when using
the current conclusion framework; and 3) the lack of specific strategies for mitigating
cognitive bias induced by exposure to task-irrelevant information. This project aims to
improve the quality of analysis in FVC cases in China by 1) empirically validating a number of speech features commonly used in FVC casework in Mandarin; and 2) exploring Chinese FVC practitioners’ perspectives on issues related to conclusion frameworks and cognitive bias.
Implicit learning of form-meaning connections: Evidence from eye tracking data
Project summary
Whether form-meaning connections can be learnt implicitly has important implications for theories of language processing and learning, but most relevant studies focused on participants’ awareness of their linguistic knowledge; the lack of awareness during the learning process has not yet been convincingly demonstrated. This project aims to determine whether real-time language learning can take place implicitly.
Funding
- Seed Fund for Basic Research for New Staff, University of Hong Kong. (PI: Ricky Chan, HKD 150,000)
- Faculty of Arts Start-up Grant, University of Hong Kong. (PI: Ricky Chan, HKD 180,000)
Effects of syllable structure on tonal coarticulation
Project summary
This project investigates how syllable structure may affect tonal alignment, tone trajectory, and tonal coarticulation in Cantonese.
Cross-linguistic study of prominence perception
Project summary
This international collaborative project uses the same procedure and stimuli to test prominence perception for speakers of typologically distinct and related varieties. In varying the prosodic properties of the languages tested, this study aims to tease apart the universal and the language-specific aspects of perceptual prominence.
Interim output
- Leemann, A., Kolly, M. J., Li, Y., Chan, R., Kwek, G. & Jesperson, A. (2016). Towards a typology of prominence perception: the role of duration. Proceedings of the 8th International Conference on Speech Prosody (SP2016). Boston, MA.
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