The effect of native language and bilingualism on multimodal perception in speech: A study of audio-aerotactile integrationa).

Previous studies of speech perception revealed that tactile sensation can be integrated into the perception of stop consonants. It remains uncertain whether such multisensory integration can be shaped by linguistic experience, such as the listener's native language(s). This study investigates audio-aerotactile integration in phoneme perception for English and French monolinguals as well as English-French bilingual listeners. Six step voice onset time continua of alveolar (/da/-/ta/) and labial (/ba/-/pa/) stops constructed from both English and French end points were presented to listeners who performed a forced-choice identification task. Air puffs were synchronized to syllable onset and randomly applied to the back of the hand. Results show that stimuli with an air puff elicited more "voiceless" responses for the /da/-/ta/ continuum by both English and French listeners. This suggests that audio-aerotactile integration can occur even though the French listeners did not have an aspiration/non-aspiration contrast in their native language. Furthermore, bilingual speakers showed larger air puff effects compared to monolinguals in both languages, perhaps due to bilinguals' heightened receptiveness to multimodal information in speech.

Production of the English /ɹ/ by Mandarin-English Bilingual Speakers.

Rhotic sounds are some of the most challenging sounds for L2 learners to acquire. This study investigates the production of English rhotic sounds by Mandarin-English bilinguals with two English proficiency levels. The production of the English /ɹ/ by 17 Mandarin-English bilinguals was examined with ultrasound imaging and compared with the production of native English speakers. The ultrasound data show that bilinguals can produce native-like bunched and retroflex gestures, but the distributional pattern of tongue shapes in various contexts differs from that of native speakers. Acoustically, the English /ɹ/ produced by bilinguals had a higher F3 and F3-F2, as well as some frication noise in prevocalic /ɹ/, features similar to the Mandarin /ɹ/. Mandarin-English bilinguals did produce language-specific phonetic realizations for the English and Mandarin /ɹ/s. There was a positive correlation between language proficiency and English-specific characteristics of /ɹ/ by Mandarin-English bilinguals in both articulation and acoustics. Phonetic similarities facilitated rather than hindered L2 speech learning in production: Mandarin-English bilinguals showed better performance in producing the English /ɹ/ allophones that were more similar to the Mandarin /ɹ/ (syllabic and postvocalic /ɹ/s) than producing the English /ɹ/ allophone that was less similar to the Mandarin /ɹ/ (prevocalic /ɹ/). This study contributes to our understanding of the mechanism of speech production in late bilinguals.

Direct neural coding of speech: Reconsideration of Whalen et al. (2006) (L).

Previous brain imaging results indicated that speech perception proceeded independently of the auditory primitives that are the product of primary auditory cortex [Whalen, Benson, Richardson, Swainson, Clark, Lai, Mencl, Fulbright, Constable, and Liberman (2006). J. Acoust. Soc. Am. 119, 575-581]. Recent evidence using electrocorticography [Hamilton, Oganian, Hall, and Chang (2021). Cell 184, 4626-4639] indicates that there is a more direct connection from subcortical regions to cortical speech regions than previous studies had shown. Although the mechanism differs, the Hamilton, Oganian, Hall, and Chang result supports the original conclusion even more strongly: Speech perception does not rely on the analysis of primitives from auditory analysis. Rather, the speech signal is processed as speech from the beginning.

Assessing accuracy of resonances obtained with reassigned spectrograms from the "ground truth" of physical vocal tract models.

The reassigned spectrogram (RS) has emerged as the most accurate way to infer vocal tract resonances from the acoustic signal [Shadle, Nam, and Whalen (2016). "Comparing measurement errors for formants in synthetic and natural vowels," J. Acoust. Soc. Am. 139(2), 713-727]. To date, validating its accuracy has depended on formant synthesis for ground truth values of these resonances. Synthesis is easily controlled, but it has many intrinsic assumptions that do not necessarily accurately realize the acoustics in the way that physical resonances would. Here, we show that physical models of the vocal tract with derivable resonance values allow a separate approach to the ground truth, with a different range of limitations. Our three-dimensional printed vocal tract models were excited by white noise, allowing an accurate determination of the resonance frequencies. Then, sources with a range of fundamental frequencies were implemented, allowing a direct assessment of whether RS avoided the systematic bias towards the nearest strong harmonic to which other analysis techniques are prone. RS was indeed accurate at fundamental frequencies up to 300 Hz; above that, accuracy was somewhat reduced. Future directions include testing mechanical models with the dimensions of children's vocal tracts and making RS more broadly useful by automating the detection of resonances.

Neural Changes in Children With Residual Speech Sound Disorder After Ultrasound Biofeedback Speech Therapy.

PURPOSE: Children with residual speech sound disorders (RSSD) have shown differences in neural function for speech production, as compared to their typical peers; however, information about how these differences may change over time and relative to speech therapy is needed. To address this gap, we used functional magnetic resonance imaging (fMRI) to examine functional activation and connectivity on adaptations of the syllable repetition task (SRT-Early Sounds and SRT-Late Sounds) in children with RSSD before and after a speech therapy program. METHOD: Sixteen children with RSSD completed an fMRI experiment before (Time 1) and after (Time 2) a speech therapy program with ultrasound visual feedback for /ɹ/ misarticulation. Progress in therapy was measured via perceptual ratings of productions of untreated /ɹ/ word probes. To control for practice effects and developmental change in patterns of activation and connectivity, 17 children with typical speech development (TD) completed the fMRI at Time 1 and Time 2. Functional activation was analyzed using a region-of-interest approach and functional connectivity was analyzed using a seed-to-voxel approach. RESULTS: Children with RSSD showed a range of responses to therapy. After correcting for multiple comparisons, we did not observe any statistically significant cross-sectional differences or longitudinal changes in functional activation. A negative relationship between therapy effect size and functional activation in the left visual association cortex was on the SRT-Late Sounds after therapy, but it did not survive correction for multiple comparisons. Significant longitudinal changes in functional connectivity were observed for the RSSD group on SRT-Early Sounds and SRT-Late Sounds, as well as for the TD group on the SRT-Early Sounds. RSSD and TD groups showed connectivity differences near the left insula on the SRT-Late Sounds at Time 2. CONCLUSION: RSSD and treatment with ultrasound visual feedback may thus be associated with neural differences in speech motor and visual association processes recruited for speech production.

Comparing metrics for quantification of children's tongue shape complexity using ultrasound imaging.

Speech sound disorders can pose a challenge to communication in children that may persist into adulthood. As some speech sounds are known to require differential control of anterior versus posterior regions of the tongue body, valid measurement of the degree of differentiation of a given tongue shape has the potential to shed light on development of motor skill in typical and disordered speakers. The current study sought to compare the success of multiple techniques in quantifying tongue shape complexity as an index of degree of lingual differentiation in child and adult speakers. Using a pre-existing data set of ultrasound images of tongue shapes from adult speakers producing a variety of phonemes, we compared the extent to which three metrics of tongue shape complexity differed across phonemes/phoneme classes that were expected to differ in articulatory complexity. We then repeated this process with ultrasound tongue shapes produced by a sample of young children. The results of these comparisons suggested that a modified curvature index and a metric representing the number of inflection points best reflected small changes in tongue shapes across individuals differing in vocal tract size. Ultimately, these metrics have the potential to reveal delays in motor skill in young children, which could inform assessment procedures and treatment decisions for children with speech delays and disorders.

Health effects of Indigenous language use and revitalization: a realist review.

BACKGROUND: Indigenous populations across the world are more likely to suffer from poor health outcomes when compared to other racial and ethnic groups. Although these disparities have many sources, one protective factor that has become increasingly apparent is the continued use and/or revitalization of traditional Indigenous lifeways: Indigenous language in particular. This realist review is aimed at bringing together the literature that addresses effects of language use and revitalization on mental and physical health. METHODS: Purposive bibliographic searches on Scopus were conducted to identify relevant publications, further augmented by forward citation chaining. Included publications (qualitative and quantitative) described health outcomes for groups of Indigenous people who either did or did not learn and/or use their ancestral language. The geographical area studied was restricted to the Americas, Australia or New Zealand. Publications that were not written in English, Spanish, French, Portuguese or German were excluded. A realist approach was followed to identify positive, neutral or negative effects of language use and/or acquisition on health, with both qualitative and quantitative measures considered. RESULTS: The bibliographic search yielded a total of 3508 possible publications of which 130 publications were included in the realist analysis. The largest proportion of the outcomes addressed in the studies (62.1%) reported positive effects. Neutral outcomes accounted for 16.6% of the reported effects. Negative effects (21.4%) were often qualified by such issues as possible cultural use of tobacco, testing educational outcomes in a student's second language, and correlation with socioeconomic status (SES), health access, or social determinants of health; it is of note that the positive correlations with language use just as frequently occurred with these issues as the negative correlations did. CONCLUSIONS: Language use and revitalization emerge as protective factors in the health of Indigenous populations. Benefits of language programs in tribal and other settings should be considered a cost-effective way of improving outcomes in multiple domains.

Formants are easy to measure; resonances, not so much: Lessons from Klatt (1986).

Formants in speech signals are easily identified, largely because formants are defined to be local maxima in the wideband sound spectrum. Sadly, this is not what is of most interest in analyzing speech; instead, resonances of the vocal tract are of interest, and they are much harder to measure. Klatt [(1986). in Proceedings of the Montreal Satellite Symposium on Speech Recognition, 12th International Congress on Acoustics, edited by P. Mermelstein (Canadian Acoustical Society, Montreal), pp. 5-7] showed that estimates of resonances are biased by harmonics while the human ear is not. Several analysis techniques placed the formant closer to a strong harmonic than to the center of the resonance. This "harmonic attraction" can persist with newer algorithms and in hand measurements, and systematic errors can persist even in large corpora. Research has shown that the reassigned spectrogram is less subject to these errors than linear predictive coding and similar measures, but it has not been satisfactorily automated, making its wider use unrealistic. Pending better techniques, the recommendations are (1) acknowledge limitations of current analyses regarding influence of F0 and limits on granularity, (2) report settings more fully, (3) justify settings chosen, and (4) examine the pattern of F0 vs F1 for possible harmonic bias.

Congruent aero-tactile stimuli bias perception of voicing continua.

Multimodal integration is the formation of a coherent percept from different sensory inputs such as vision, audition, and somatosensation. Most research on multimodal integration in speech perception has focused on audio-visual integration. In recent years, audio-tactile integration has also been investigated, and it has been established that puffs of air applied to the skin and timed with listening tasks shift the perception of voicing by naive listeners. The current study has replicated and extended these findings by testing the effect of air puffs on gradations of voice onset time along a continuum rather than the voiced and voiceless endpoints of the original work. Three continua were tested: bilabial ("pa/ba"), velar ("ka/ga"), and a vowel continuum ("head/hid") used as a control. The presence of air puffs was found to significantly increase the likelihood of choosing voiceless responses for the two VOT continua but had no effect on choices for the vowel continuum. Analysis of response times revealed that the presence of air puffs lengthened responses for intermediate (ambiguous) stimuli and shortened them for endpoint (non-ambiguous) stimuli. The slowest response times were observed for the intermediate steps for all three continua, but for the bilabial continuum this effect interacted with the presence of air puffs: responses were slower in the presence of air puffs, and faster in their absence. This suggests that during integration auditory and aero-tactile inputs are weighted differently by the perceptual system, with the latter exerting greater influence in those cases where the auditory cues for voicing are ambiguous.

Baseline Stimulability Predicts Patterns of Response to Traditional and Ultrasound Biofeedback Treatment for Residual Speech Sound Disorder.

PURPOSE: This study aimed to identify predictors of response to treatment for residual speech sound disorder (RSSD) affecting English rhotics. Progress was tracked during an initial phase of traditional motor-based treatment and a longer phase of treatment incorporating ultrasound biofeedback. Based on previous literature, we focused on baseline stimulability and sensory acuity as predictors of interest. METHOD: Thirty-three individuals aged 9-15 years with residual distortions of /ɹ/ received a course of individual intervention comprising 1 week of intensive traditional treatment and 9 weeks of ultrasound biofeedback treatment. Stimulability for /ɹ/ was probed prior to treatment, after the traditional treatment phase, and after the end of all treatment. Accuracy of /ɹ/ production in each probe was assessed with an acoustic measure: normalized third formant (F3)-second formant (F2) distance. Model-based clustering analysis was applied to these acoustic measures to identify different average trajectories of progress over the course of treatment. The resulting clusters were compared with respect to acuity in auditory and somatosensory domains. RESULTS: All but four individuals were judged to exhibit a clinically significant response to the combined course of treatment. Two major clusters were identified. The "low stimulability" cluster was characterized by very low accuracy at baseline, minimal response to traditional treatment, and strong response to ultrasound biofeedback. The "high stimulability" group was more accurate at baseline and made significant gains in both traditional and ultrasound biofeedback phases of treatment. The clusters did not differ with respect to sensory acuity. CONCLUSIONS: This research accords with clinical intuition in finding that individuals who are more stimulable at baseline are more likely to respond to traditional intervention, whereas less stimulable individuals may derive greater relative benefit from biofeedback. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.20422236.

Characterizing sensorimotor profiles in children with residual speech sound disorder: a pilot study.

PURPOSE: Children with speech errors who have reduced motor skill may be more likely to develop residual errors associated with lifelong challenges. Drawing on models of speech production that highlight the role of somatosensory acuity in updating motor plans, this pilot study explored the relationship between motor skill and speech accuracy, and between somatosensory acuity and motor skill in children. Understanding the connections among sensorimotor measures and speech outcomes may offer insight into how somatosensation and motor skill cooperate during speech production, which could inform treatment decisions for this population. METHOD: Twenty-five children (ages 9-14) produced syllables in an /ɹ/ stimulability task before and after an ultrasound biofeedback treatment program targeting rhotics. We first tested whether motor skill (as measured by two ultrasound-based metrics of tongue shape complexity) predicted acoustically measured accuracy (the normalized difference between the second and third formant frequencies). We then tested whether somatosensory acuity (as measured by an oral stereognosis task) predicted motor skill, while controlling for auditory acuity. RESULTS: One measure of tongue shape complexity was a significant predictor of accuracy, such that higher tongue shape complexity was associated with lower accuracy at pre-treatment but higher accuracy at post-treatment. Based on the same measure, children with better somatosensory acuity produced /ɹ/ tongue shapes that were more complex, but this relationship was only present at post-treatment. CONCLUSION: The predicted relationships among somatosensory acuity, motor skill, and acoustically measured /ɹ/ production accuracy were observed after treatment, but unexpectedly did not hold before treatment. The surprising finding that greater tongue shape complexity was associated with lower accuracy at pre-treatment highlights the importance of evaluating tongue shape patterns (e.g., using ultrasound) prior to treatment, and has the potential to suggest that children with high tongue shape complexity at pre-treatment may be good candidates for ultrasound-based treatment.

Phonetic Documentation in Three Collections: Topics and Evolution.

Phonetic aspects of many languages have been documented, though the breadth and focus of such documentation varies substantially. In this survey, phonetic aspects (here called "categories") that are typically reported were assessed in three English-language collections-the Illustrations of the IPA, articles from the Journal of Phonetics, and papers from the Ladefoged/Maddieson Sounds of the World's Languages (SOWL) documentation project. Categories were defined for consonants (e.g., Voice Onset Time (VOT) and frication spectrum; 10 in total), vowels (e.g., formants and duration; 7 total) and suprasegmentals (e.g., stress and distinctive vowel length, 6 total). The Illustrations, due to their brevity, had, on average, limited coverage of the selected categories (12% of the 23 categories). Journal of Phonetics articles were typically theoretically motivated, but 64 had sufficient measurements to count as phonetic documentation; these also covered 12% of the categories. The SOWL studies, designed to cover as much of the phonetic structure as feasible in an article-length treatment, achieved 41% coverage on average. Four book-length studies were also examined, with an average of 49% coverage. Phonetic properties of many language families have been studied, though Indo-European is still disproportionately represented. Physiological measures were excluded as being less common, and perceptual measures were excluded as being typically more theoretical. This preliminary study indicates that certain acoustic properties of languages are typically measured and may be considered as an impetus for later, fuller coverage, but broader consensus on the categories is needed. Current documentation efforts could be more useful if these considerations were addressed.

Comparison of auto-contouring and hand-contouring of ultrasound images of the tongue surface.

Contours traced by trained phoneticians have been considered to be the most accurate way to identify the midsagittal tongue surface from ultrasound video frames. In this study, inter-measurer reliability was evaluated using measures that quantified both how closely human-placed contours approximated each other as well as how consistent measurers were in defining the start and end points of contours. High reliability across three measurers was found for all measures, consistent with treating contours placed by trained phoneticians as the 'gold standard.' However, due to the labour-intensive nature of hand-placing contours, automatic algorithms that detect the tongue surface are increasingly being used to extract tongue-surface data from ultrasound videos. Contours placed by six automatic algorithms (SLURP, EdgeTrak, EPCS, and three different configurations of the algorithm provided in Articulate Assistant Advanced) were compared to human-placed contours, with the same measures used to evaluate the consistency of the trained phoneticians. We found that contours defined by SLURP, EdgeTrak, and two of the AAA configurations closely matched the hand-placed contours along sections of the image where the algorithms and humans agreed that there was a discernible contour. All of the algorithms were much less reliable than humans in determining the anterior (tongue-tip) edge of tongue contours. Overall, the contours produced by SLURP, EdgeTrak, and AAA should be useable in a variety of clinical applications, subject to spot-checking. Additional practical considerations of these algorithms are also discussed.

The effect of gap duration on the perception of fluent versus disfluent speech.

PURPOSE: Gap duration contributes to the perception of utterances as fluent or disfluent, but few studies have systematically investigated the impact of gap duration on fluency judgments. The purposes of this study were to determine how gaps impact disfluency perception, and how listener background and experience impact these judgments. METHODS: Sixty participants (20 adults who stutter [AWS], 20 speech-language pathologists [SLPs], and 20 naïve listeners) listened to four tokens of the utterance, "Buy Bobby a puppy," produced at typical speech rates. The gap duration between "Buy" and "Bobby" was systematically manipulated with gaps ranging from 23.59 ms to 325.44 ms. Participants identified stimuli as fluent or disfluent. RESULTS: The disfluency threshold - the point at which 50 % of trials were categorized as disfluent - occurred at a gap duration of 126.46 ms, across all participants and tokens. The SLPs exhibited higher disfluency thresholds than the AWS and the naïve listeners. CONCLUSION: This study determined, based on the specific set of stimuli used, when the perception of utterances tends to shift from fluent to disfluent. Group differences indicated that SLPs are less inclined to identify disfluencies in speech potentially because they aim to be less critical of speech that deviates from "typical".

Extending Ultrasound Tongue Shape Complexity Measures to Speech Development and Disorders.

Purpose Generalizations can be made about the order in which speech sounds are added to a child's phonemic inventory and the ways that child speech deviates from adult targets in a given language. Developmental and disordered speech patterns are presumed to reflect differences in both phonological knowledge and skilled motor control, but the relative contribution of motor control remains unknown. The ability to differentially control anterior versus posterior regions of the tongue increases with age, and thus, complexity of tongue shapes is believed to reflect an individual's capacity for skilled motor control of speech structures. Method The current study explored the relationship between tongue complexity and phonemic development in children (ages 4-6 years) with and without speech sound disorder producing various phonemes. Using established metrics of tongue complexity derived from ultrasound images, we tested whether tongue complexity incrementally increased with age in typical development, whether tongue complexity differed between children with and without speech sound disorder, and whether tongue complexity differed based on perceptually rated accuracy (correct vs. incorrect) for late-developing phonemes in both diagnostic groups. Results Contrary to hypothesis, age was not significantly associated with tongue complexity in our typical child sample, with the exception of one association between age and complexity of /t/ for one measure. Phoneme was a significant predictor of tongue complexity, and typically developing children had more complex tongue shapes for /ɹ/ than children with speech sound disorder. Those /ɹ/ tokens that were rated as perceptually correct had higher tongue complexity than the incorrect tokens, independent of diagnostic classification. Conclusions Quantification of tongue complexity can provide a window into articulatory patterns characterizing children's speech development, including differences that are perceptually covert. With the increasing availability of ultrasound imaging, these measures could help identify individuals with a prominent motor component to their speech sound disorder and could help match those individuals with a corresponding motor-based treatment approach. Supplemental Material https://doi.org/10.23641/asha.14880039.

A dual mechanism for intrinsic f0.

Vowel-intrinsic fundamental frequency (IF0), the phenomenon that high vowels tend to have a higher fundamental frequency (f0) than low vowels, has been studied for over a century, but its causal mechanism is still controversial. The most commonly accepted "tongue-pull" hypothesis successfully explains the IF0 difference between high and low vowels but fails to account for gradient IF0 differences among low vowels. Moreover, previous studies that investigated the articulatory correlates of IF0 showed inconsistent results and did not appropriately distinguish between the tongue and the jaw. The current study used articulatory and acoustic data from two large corpora of American English (44 speakers in total) to examine the separate contributions of tongue and jaw height on IF0. Using data subsetting and stepwise linear regression, the results showed that both the jaw and tongue heights were positively correlated with vowel f0, but the contribution of the jaw to IF0 was greater than that of the tongue. These results support a dual mechanism hypothesis in which the tongue-pull mechanism contributes to raising f0 in non-low vowels while a secondary "jaw-push" mechanism plays a more important role in lowering f0 for non-high vowels.

Vowel Acoustics and Speech Intelligibility in Young Adults With Down Syndrome.

Purpose Speech production deficits and reduced intelligibility are frequently noted in individuals with Down syndrome (DS) and are attributed to a combination of several factors. This study reports acoustic data on vowel production in young adults with DS and relates these findings to perceptual analysis of speech intelligibility. Method Participants were eight young adults with DS as well as eight age- and gender-matched typically developing (TD) controls. Several different acoustic measures of vowel centralization and variability were applied to tokens of corner vowels (/ɑ/, /æ/, /i/, /u/) produced in common English words. Intelligibility was assessed for single-word productions of speakers with DS, by means of transcriptions from 14 adult listeners. Results Group differentiation was found for some, but not all, of the acoustic measures. Low vowels were more acoustically centralized and variable in speakers with DS than TD controls. Acoustic findings were associated with overall intelligibility scores. Vowel formant dispersion was the most sensitive measure in distinguishing DS and TD formant data. Conclusion Corner vowels are differentially affected in speakers with DS. The acoustic characterization of vowel production and its association with speech intelligibility scores within the DS group support the conclusion of motor control deficits in the overall speech impairment. Implications are discussed for effective treatment planning.

Effects of Ultrasound Familiarization on Production and Perception of Nonnative Contrasts.

BACKGROUND/AIMS: We investigated the efficacy of ultrasound imaging of the tongue as a tool for familiarizing naïve learners with the production of a class of nonnative speech sounds: palatalized Russian consonants. METHODS: Two learner groups were familiarized, one with ultrasound and one with audio only. Learners performed pre- and postfamiliarization production and discrimination tasks. RESULTS: Ratings of productions of word-final palatalized consonants by learners from both groups improved after familiarization, as did discrimination of the palatalization contrast word-finally. There were no significant differences in the improvement between groups in either task. All learners were able to generalize to novel contexts in production and discrimination. The presence of palatalization interfered with discrimination of word-initial manner, and ultrasound learners were more successful in overcoming that interference. CONCLUSION: Ultrasound familiarization resulted in improvements in production and discrimination comparable to audio only. Ultrasound familiarization additionally helped learners overcome difficulties in manner discrimination introduced by palatalization. When familiarizing learners with a novel, nonnative class of sounds, a small set of stimuli in different contexts may be more beneficial than using a larger set in one context. Although untrained production can disrupt discrimination training, we found that production familiarization was not disruptive to discrimination or production.

Voice Onset Time and beyond: Exploring laryngeal contrast in 19 languages.

In this special collection entitled Marking 50 Years of Research on Voice Onset Time and the Voicing Contrast in the World's Languages, we have compiled eleven studies investigating the voicing contrast in 19 languages. The collection provides extensive data obtained from 270 speakers across those languages, examining VOT and other acoustic, aerodynamic and articulatory measures. The languages studied may be divided into four groups: 'aspirating' languages with a two-way contrast (English, three varieties of German); 'true voicing' languages with a two-way contrast (Russian, Turkish, Brazilian Portuguese, two Iranian languages Pashto and Wakhi); languages with a three-way contrast (Thai, Vietnamese, Khmer, Yerevan Armenia, three Indo-Aryan languages, Dawoodi, Punjabi and Shina, and Burushaki spoken in India); and Indo-Aryan languages with a more than three-way contrast (Jangli and Urdu with a four-way contrast, and Sindhi and Siraiki with a five-way contrast). We discuss the cross-linguistic data, focusing on how much VOT alone tell s us above the voicing contrast in these languages, and what other phonetic dimensions (such as consonant-induced F0 and voice quality) are needed for a complete understanding of laryngeal contrast in these languages. Implications for various issues emerge: universal phonetic feature systems, effects of language contact on linguistic levelling, and the relation between laryngeal contrast and supralaryngeal articulation. The cross-linguistic VOT data also lead us to discuss how the distribution of VOT as measured acoustically may allow us to infer the underlying articulation and how it might be approached in gestural phonologies. The discussion on these multiple issues sparks new questions to be resolved, and provide indications of where the field may be best directed in exploring laryngeal contrast in voicing in the world's languages.

F0-induced formant measurement errors result in biased variabilities.

Many developmental studies attribute reduction of acoustic variability to increasing motor control. However, linear prediction-based formant measurements are known to be biased toward the nearest harmonic of F0, especially at high F0s. Thus, the amount of reported formant variability generated by changes in F0 is unknown. Here, 470 000 vowels were synthesized, mimicking statistics reported in four developmental studies, to estimate the proportion of formant variability that can be attributed to F0 bias, as well as other formant measurement errors. Results showed that the F0-induced formant measurements errors are large and systematic, and cannot be eliminated by a large sample size.