Christina Kuo

Vowel reduction across tasks for male speakers of American Englisha)

This study examined acoustic variation of vowels within speakers across speech tasks. The overarching goal of the study was to understand within-speaker variation as one index of the range of normal speech motor behavior for American English vowels. Ten male speakers of American English performed four speech tasks including citation form sentence reading with a clear-speech style (clear-speech), citation form sentence reading (citation), passage reading (reading), and conversational speech (conversation). Eight monophthong vowels in a variety of consonant contexts were studied. Clear-speech was operationally defined as the reference point for describing variation. Acoustic measures associated with the conventions of vowel targets were obtained and examined. These included temporal midpoint formant frequencies for the first three formants (F1, F2, and F3) and the derived Euclidean distances in the F1-F2 and F2-F3 planes. Results indicated that reduction toward the center of the F1-F2 and F2-F3 planes increased in magnitude across the tasks in the order of clear-speech, citation, reading, and conversation. The cross-task variation was comparable for all speakers despite fine-grained individual differences. The characteristics of systematic within-speaker acoustic variation across tasks have potential implications for the understanding of the mechanisms of speech motor control and motor speech disorders.

Vowel contrasts relative to schwa across tasks: Preliminary findings for Parkinson’s disease

The purpose of this study is to quantify acoustic contrasts of vowels in relation to the mid-central unrounded vowel schwa produced by speakers with Parkinson’s disease (PD) in different speaking tasks. The study is motivated by a hypothesis that schwa may serve as a speaker-specific reference for vowel contrasts given its associated anatomical properties of a neutral vocal tract. For the present study, a speaker-specific reference schwa is identified from averaged first and second formant (F1 and F2) frequencies of unstressed article “a” productions in citation form. Two questions are addressed. First, can speaking-task related changes in vowel contrasts be expressed by vowel-schwa distances in the acoustic space consistently across speakers? Second, do characteristics of schwa-referenced vowel contrasts differ for speakers with PD and healthy speakers? F1 and F2 frequencies of schwa and vowels /i/, /a/, and /u/ in three tasks including clear-speech, sentence reading, and passage reading are examined. Th...

Vowel contrasts relative to schwa: Effects of utterance-level fundamental frequency

The purpose of this study is to characterize the potential effects of utterance-level fundamental frequency (F0) on the acoustic contrasts of vowels as expressed relative to the mid-central vowel schwa. This is a follow-up to a previous study [Kuo, J. Acoust. Soc. Am. 141, 3840 (2017)] based on a hypothesis of schwa as a speaker-defined reference for vowel contrasts. The hypothesized reference schwa is made up of the averaged first and second formant (F1 and F2) frequencies from many tokens of schwa produced by a given speaker. Motivated by the potential interactions among F0, spectral sampling, and articulation, the present study evaluates the effects, if any, of utterance-level F0 on vowel contrasts relative to schwa. Utterance-level F0 is measured for breath groups at the sentence level. Vowel contrasts are expressed as the Euclidean distances between vowels and the reference schwa in the F1-F2 space. Specifically, two questions are of interest. First, are the Euclidean distances between vowels and the...

American English schwa characteristics in the context of vowel reduction

The mid-central unrounded vowel schwa has been understood as a vocalic produced with a uniform cross-sectional area of the vocal tract that is correlated with formant frequencies occupying the center of the acoustic vowel space. As such, schwas have also been associated with reduced vowels. Vowel reduction occurs in a variety of contexts and factors, and it is commonly described as centralization toward the middle of the vowel space or a migration of formant frequencies toward those associated with a tube of uniform cross-sectional areas. Nonetheless, little is known regarding the extent to which reduced vowels approximate schwa values. The purpose of this study was to establish a within-speaker reference of schwa in the context of vowel reduction. Two questions were addressed. First, do the acoustic characteristics of schwa correspond to the centroid of vowel space? Second, how do schwa values compare to those of reduced vowels? Formant frequencies of vowels in citation and connected speech tasks were co...

The relationship between fundamental frequency and within-speaker vowel reduction

The contribution(s) of fundamental frequency (F0) to vowel production has potential theoretical and clinical implications. The sufficient contrast hypothesis [Diehl et al., J. Phon. 24, 187–208 (1996)] suggests that a high F0 is associated with effects of spectral undersampling, and thus may require more exaggerated formant frequencies to maintain the perceptual distinctiveness of vowels. Nonetheless, studies on the interplay between F0 and vowel acoustics would appear inconclusive [Byrd, J. Acoust. Soc. Am. 92, 593–596 (1992)] [Weirich & Simpson, J. Acoust. Soc. Am. 134, 2965–2974 (2013)]. This study evaluated the sufficient contrast hypothesis as a within-speaker mechanism, with an overarching hypothesis that formant frequency exaggeration associated with spectral undersampling, if any, occurs within a given production system (i.e., speaker). To this end, formant frequencies of vowels and F0 were obtained for the same speaker across different speaking tasks. Within speaker, it was hypothesized that vowel formant frequencies as well as F0 change across tasks. More importantly, average F0 is hypothesized to be negatively correlated with the degree of vowel formant frequency reduction within-speaker across tasks. That is, a vowel system produced with a higher F0 would be less prone to reduction because the spectral peaks are better defined. The contribution(s) of fundamental frequency (F0) to vowel production has potential theoretical and clinical implications. The sufficient contrast hypothesis [Diehl et al., J. Phon. 24, 187–208 (1996)] suggests that a high F0 is associated with effects of spectral undersampling, and thus may require more exaggerated formant frequencies to maintain the perceptual distinctiveness of vowels. Nonetheless, studies on the interplay between F0 and vowel acoustics would appear inconclusive [Byrd, J. Acoust. Soc. Am. 92, 593–596 (1992)] [Weirich & Simpson, J. Acoust. Soc. Am. 134, 2965–2974 (2013)]. This study evaluated the sufficient contrast hypothesis as a within-speaker mechanism, with an overarching hypothesis that formant frequency exaggeration associated with spectral undersampling, if any, occurs within a given production system (i.e., speaker). To this end, formant frequencies of vowels and F0 were obtained for the same speaker across different speaking tasks. Within speaker, it was hypothesized that vowe...

Diphthong formant transitions in four speaking tasks.

Diphthongs have been demonstrated to have longer durations and to involve more extensive articulatory gestures, reflected as larger frequency changes, when compared to monophthongs [Lehiste, I., and Peterson, G. E., J. Acoust. Soc. Am. 33, 268–277 (1961); Holbrook, A. and Fairbanks, G., J. Speech Hear. Res. 5, 38–58 (1962)]. However, limited work has documented the nature of diphthong variability. This study describes and examines diphthong formant transitions in the speech production of ten healthy male native speakers of American English, with Wisconsin dialects, to identify and evaluate the pattern, if any, of diphthong variability in four speaking tasks: conversational speech, story reading, sentence in citation form, sentence in clear speech. The study is motivated by the phenomenon of vowel reduction [Lindblom, J. Acoust. Soc. Am. 35, 1773–1781 (1963)], which has been documented widely for monophthongs, as well as speaking rate‐induced changes in diphthong formant transitions [Gay, T., J. Acoust. So...

Transition characteristics in speakers with dysarthria and in healthy controls: Part IV: Additional data on vital capacity transitions and stroke patients.

Formant transitions are known to provide important cues for speech perception, sound identification, and inferences to articulatory behavior. This study describes and examines three types of formant transitions [consonant‐vowel (CV), vowel‐consonant (VC), and diphthong transitions] in four groups of speakers: healthy, ALS, Parkinson’s disease, and stroke. This is an extension from previous work by Weismer et al. [J. Acoust. Soc. Am. 121, 3135 (2007)] and Weismer et al. [J. Acoust. Soc. Am. 124, 2558 (2008)], who showed shallower slopes for CV and diphthong transitions in persons with dysarthria (ALS and PD). To better understand the characteristics of the different transition types in healthy and disordered populations, two questions are addressed here. First, are CV transitions associated with dysarthria different from those in healthy speakers in a way comparable to the observed differences in diphthong transitions? Second, do VC transitions show the same normal characteristics, and are the differences ...

Speaker variability when producing repeated syllables and across speech tasks.

Target theory [Lindblom, J. Acoust. Soc. Am. 35, 1773–1781 (1963)] of vowel perception and production suggests that vowels have unique and characteristic articulatory and acoustic events that constitute the canonical forms (“targets”) of vowels. However, speakers do not always achieve these targets. There exists substantial variability in speech within a speaker and across speakers. Some of the challenges in understanding speech production lie in variability resulting from various factors including speaker identity, prosody, rate, and speech task. Because of the lack of data permitting good statistical estimates of target events, the following experiments were performed. First, within‐speaker variations in consonant‐vowel (CV) and vowel‐consonant transitions in three monosyllabic words (dock, knock, and shock) during a sentence reading repetition task are evaluated for two speakers. Second, acoustic vowel targets in /h/‐vowel‐/d/ or‐/t/ and selected consonant contexts (CV‐/d/ or‐/t/) are studied in the sp...

Transition characteristics in speakers with dysarthria and in healthy controls: Part III: liquids and glides.

In two previous reports [Weismer, Kuo, & Chung, J. Acoust. Soc. Am. 121, 3135 (2007); Kuo and Weismer, J. Acoust. Soc. Am. 124, 2558 (2008)] the transition characteristics of speakers with dysarthria, secondary to Parkinson disease and amyotrophic lateral sclerosis (ALS), were compared to transition characteristics of healthy controls. The previous reports described the characteristics of obstruent‐vowel [Weismer >etal/> (2007)] and diphthong [Kuo and Weismer (2008)] transitions extracted from an extended passage reading. Our hypothesis was that distributional analyses would show the CV, obstruent‐vowel transitions to be less affected by the neurological disease as compared to diphthong transitions. The hypothesis was not supported by the data, which showed both types of transitions to be slower and less extensive than in healthy controls. The present report completes this analysis with documentation of transition characteristics of liquids and glides. Our expectation is that liquid and glide transition t...

Consonant‐vowel and diphthong transitions in the speech of persons with dysarthria and of healthy controls.

Formant transitions have been of interest to researchers for their contribution to speech perception, sound identification, and inferences to articulatory behavior. In previous work diphthong transitions have been shown to be sensitive to speech motor control deficits found in dysarthria; comparable data regarding transitions between obstruents (i.e., consonants) and vowels are not available. Here consonant‐vowel (CV) and diphthong transitions in speakers with dysarthria and in healthy controls are examined to understand whether the effects for diphthong transitions observed in speakers with dysarthria—reduced extent and slope and occasionally lengthened duration—are present for CV transitions. The first part of this study extends work by Weismer et al. [J. Acoust. Soc. Am. 121, 3135 (2007)], who reported a tendency for shallower CV transitions in speakers with dysarthria when compared to healthy controls, but only for syllables where C=dorsal. Given the limited number of dorsal CV transitions in the prev...