School of Languages and Linguistics - Research Publications
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ItemNo Preview AvailableAcoustic analysis of the effects of sustained wakefulness on speech(ACOUSTICAL SOC AMER AMER INST PHYSICS, 2010-12)Exposing healthy adults to extended periods of wakefulness is known to induce changes in psychomotor functioning [Maruff et al. (2005). J. Sleep Res. 14, 21-27]. The effect of fatigue on speech is less well understood. To date, no studies have examined the pitch and timing of neurologically healthy individuals over 24 h of sustained wakefulness. Therefore, speech samples were systematically acquired (e.g., every 4 h) from 18 healthy adults over 24 h. Stimuli included automated and extemporaneous speech tasks, sustained vowel, and a read passage. Measures of timing, frequency and spectral energy were derived acoustically using PRAAT and significant changes were observed on all tasks. The effect of fatigue on speech was found to be strongest just before dawn (after 22 h). Specifically, total speech time, mean pause length, and total signal time all increased as a function of increasing levels of fatigue on the reading tasks; percentage pause and mean pause length decreased on the counting task; F4 variation decreased on the sustained vowel tasks /a:/; and alpha ratio increased on the extemporaneous speech tasks. These findings suggest that acoustic methodologies provide objective data on central nervous system functioning and that changes in speech production occur in healthy adults after just 24 h of sustained wakefulness.
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ItemNo Preview AvailableReliability, stability, and sensitivity to change and impairment in acoustic measures of timing and frequency(Elsevier Inc., 2011)Assessment of the voice for supporting classifications of central nervous system (CNS) impairment requires a different practical, methodological, and statistical framework compared with assessment of the voice to guide decisions about change in the CNS. In experimental terms, an understanding of the stability and sensitivity to change of an assessment protocol is required to guide decisions about CNS change. Five experiments (N=70) were conducted using a set of commonly used stimuli (eg, sustained vowel, reading, extemporaneous speech) and easily acquired measures (eg, f0–f4, percent pause). Stability of these measures was examined through their repeated application in healthy adults over brief and intermediate retest intervals (ie, 30 seconds, 2 hours, and 1 week). Those measures found to be stable were then challenged using an experimental model that reliably changes voice acoustic properties (ie, the Lombard effect). Finally, adults with an established CNS-related motor speech disorder (dysarthria) were compared with healthy controls. Of the 61 acoustic variables studied, 36 showed good stability over all three stability experiments (eg, number of pauses, total speech time, speech rate, f0–f4). Of the measures with good stability, a number of frequency measures showed a change in response to increased vocal effort resulting from the Lombard effect challenge. Furthermore, several timing measures significantly separated the control and motor speech impairment groups. Measures with high levels of stability within healthy adults, and those that show sensitivity to change and impairment may prove effective for monitoring changes in CNS functioning.
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ItemThe acoustic characteristics of diphthongs in Indian English(Wiley, 2010-01-01)This paper presents the results of an acoustic analysis of English diphthongs produced by three L1 speakers of Hindi and four L1 speakers of Punjabi. Formant trajectories of rising and falling diphthongs (i.e., vowels where there is a clear rising or falling trajectory through the F1/F2 vowel space) were analysed in a corpus of citation-form words. In line with previous research, the diphthong inventory included six different diphthongs and a long monophthongal vowel [OI] in place of/partial derivative U/in GOAT; however, none of the speakers produced a full set of diphthong vowels. In addition, the/eI/diphthong, as in FACE, and the/U partial derivative/diphthong, as in TOUR, had both monophthongal and diphthongal realizations depending on the speaker. Overall, there was a great deal of variation in diphthong realization across the corpus but L1 appeared to be a relevant factor. Punjabi speakers showed a wider range of phonetic realizations for some of the vowels, and were more likely to produce long monophthongs rather than diphthongs. The results also highlight differences in the phonetic characteristics of several diphthongs between the speakers of two language backgrounds. The results of this study therefore contribute to the debate on the phonemic representation of IE vowels by taking into account different L1 influence (i.e., Hindi or Punjabi).