Stop Closure Research Articles

A Duration-Dependent Account of Coarticulation for Hyper- and Hypoarticulation

Previous studies investigating anticipatory coarticulation in emphatically stressed CV sequences and during fast speaking rates reported that three factors contributed to the overall extent of the documented coarticulation. These factors were: (1) vowel identity, (2) vowel space expansion (emphasis) or reduction (fast rate), and a hypothesized (3) ‘deeper’ and ‘shallower’ stop closure contact in emphatic and faster speech, respectively. The objective of the current research was to conceptually and quantitatively unify these two studies. This was accomplished by showing that the opposite changes to frequency onsets of F2 transitions due to emphatic and rapid speech systematically vary as a function of the durational changes in the stop closure interval. Specifically, the decrease in coarticulation in emphatic speech is characterized by increases in F2 onsets and longer stop closures (relative to a normal baseline); the increase in coarticulation due to rapid speech shows concomitant decreases in F2 onsets coinciding with shorter stop closure intervals. Vocal tract area function simulations corresponding to emphatic and reduced speech implicitly support ‘deeper’ and ‘shallower’ closure contacts as a third factor contributing to the overall extent of anticipatory CV coarticulation.

Acoustics and perception of velar softening for unaspirated stops

This paper provides articulatory, acoustic and perceptual data in support of the hypothesis that the velar softening process through which /k/ becomes /tʃ/ is based on articulation rather than on acoustic equivalence if operating on unaspirated stops. Production data for unaspirated /k/ are analyzed for five speakers of Majorcan Catalan, where the velar stop phoneme exhibits (alveolo)palatal or velar allophones depending on vowel context and position. Data on several parameters, i.e., contact anteriority and dorsopalatal contact degree, burst spectral peak frequency, energy and duration, and F2 and F3 vowel transition endpoints and ranges, suggest that /tʃ/ may have originated from (alveolo)palatal stop realizations not only before front vocalic segments but also before low and central vowels and word finally. Perception results are consistent with the production data in indicating that the most significant /tʃ/ perception cues are burst energy before /a, u/ and burst duration word/utterance finally. They also suggest that velar softening for unaspirated /k/ before front vocalic segments is triggered by an increase in burst frication energy and duration resulting from the narrowing of an (alveolo)palatal central channel occurring at stop closure release. These findings are in agreement with the existence of contextual and positional (alveolo)palatal stop allophones of /k/, and with evidence from sound change, in the Romance languages.

Lengthened affricates as a test case for the phonetics–phonology interface

Many phonetic and phonological processes resemble one another, which has led some researchers to suggest that phonetics and phonology are essentially the same. This study compares phonetic and phonological processes of consonant lengthening by analyzing duration measurements collected from Hungarian speakers (n = 14). Affricates, which crucially possess a two-part structure, were placed in target positions. Results show that affricates regularly undergo phonetic lengthening at phrase boundaries, and the affected portion of the affricate is always that which lies closer to the boundary. Affricates also regularly undergo phonological lengthening when next to a geminating suffix, but the affected portion of the affricate is always the stop closure. Thus, while phonetic lengthening observes a strict respect for locality, phonological lengthening does not, and we conclude that the two processes are in fact quite different from one another.

Estimation of Place of Articulation During Stop Closures of Vowel–Consonant–Vowel Utterances

Production of vowel-oral stop consonant-vowel utterances involves movement of articulators from the articulatory position of the initial vowel towards that of the oral stop closure, and then to that of the final vowel. As the closure segments have zero or low signal energy, linear predictive coding (LPC)-based estimation of vocal tract shape fails during stop closure. This paper reports a technique for estimation of place of articulation during stop closures by performing bivariate polynomial modeling on vocal tract area values during transition segments preceding and following the closure. The technique with second-degree polynomial modeling was found to be suitable for estimating the place of maximum constriction during stop closure segments of vowel-consonant-vowel utterances with bilabial, alveolar, and velar stops. The estimated places compared well with the actual constriction locations observed from the articulatory data. The technique may be useful for improving effectiveness of speech-training aids for production of stop consonants by providing visual feedback of the estimated place of articulation.

Phonetic realization of glottal stop in Shugni.

Shugni is an underdocumented Indo‐European language, mainly spoken in the Pamir mountains. Orthographically, Shugni used the apostrophe to symbolize the glottal stop phoneme, and the symbol only occurred word initially. In this paper, phonetic manifestation of glottal stop was examined, and the adjacent vowel [a] was compared under five conditions: (1) word‐initial glottal stop followed by [a] and a consonant #[ʔaC1], (2) word‐medial [C2aC1] sequence where [a] was also syllable‐medial, (3) word‐medial [C2aC1] sequence where [a] was syllable‐final, (4) word‐final [a] preceded by a consonant [C2a]#, and (5) a sequence of [C2a]# [ʔaC1] where glottal stop was word‐initial and intervocalic. Four acoustic parameters were measured, and glottal stop was defined as (1) an absence of formant transitions entering or leaving [a], (2) an abrupt start or end of [a]’s magnitude, (3) identifiable stop closure, and (4) irregular pulses produced by glottal tension. The results showed that irregular pulses were noticed in some but not all [a]s of words which began with the apostrophe. No other significant acoustic differences were noted among conditions. The results suggested that glottal stop in Shugni be described as non‐phonemic vowel laryngealization or creaky phonation. The word‐initial apostrophe had to be treated cautiously to interpret the variation.

On the status of terminal devoicing as an interlanguage process among Brazilian learners of English

This paper investigates the status of Terminal Devoicing in the light of connectionism, by revisiting this process in a more dynamic framework. It focuses on the acquisition of two acoustic cues that distinguish final voiced from voiceless stops in English: (1) percentage of voicing in the stop closure; (2) length of the vowel that precedes the obstruent. Data obtained from Brazilian students of English were compared to those collected from American speakers, in order to check whether the learners' productions differed significantly from native speech. Results showed that neither voicing in the closure nor vowel length were totally neutralized, which indicates that learners are starting to distinguish final voiceless and voiced stops.

Variation in stop consonant voicing in two regional varieties of American English.

This study is an acoustic investigation of the nature and extent of consonant voicing of the stop /b/ in two dialectal varieties of American English spoken in south‐central Wisconsin and western North Carolina. The stop /b/ occurred at the juncture of two words such as small bids, in a position between two voiced sonorants, i.e., the liquid /l/ and a vowel. Twenty women participated, ten representing the Wisconsin and the North Carolina variety, respectively. Significant dialectal differences were found in the voicing patterns. The Wisconsin stop closures were usually not fully voiced and terminated in a complete silence followed by a noisy and voiceless closure release, whereas North Carolina speakers produced mostly fully voiced closures. Further dialectal differences included the proportion of closure voicing as a function of word emphasis. For Wisconsin speakers, the proportion of closure voicing was smallest when the word was emphasized and it was greatest in nonemphatic positions. For North Carolina speakers, the degree of word emphasis did not have an effect on the proportion of closure voicing. The results are discussed in terms of differences in the way voicing is maintained during the closure by the speakers of respective dialects. [Work supported by NIH..]

Semiautomatic measures of velar stop closure location using the EdgeTrak software.

Previous work has found a strong correlation between the frontness of closure location for velar stops (measured manually from ultrasound images) and the frontness of the following vowel (measured by F2). In this study, semi automatic measures of tongue frontness during a velar closure were made. Tongue edge traces were made using the EDGETRAK software (Li et al., 2005, Clinical Linguistics and Phonetics, 545–554). Frontness was then quantified from these traces using three different measures: Bressman’s anteriority index (Bressman et al., 2005, Clinical Linguistics and Phonetics, 573–588), a modified version of the anteriority index created for this study, and a measure of the center of mass of the tongue created for this study. When compared to the original manual measures, the modified anteriority index correlated most highly with both the manual measurement of the consonant closure location and also with F2 of the following vowel. The modified anteriority index uses an angle based weight in the anteriority calculation (as opposed to the arbitrary weights of Bressman’s anteriority index). The center of mass was the worst performing measure, and it appeared to be overly sensitive to the extreme anterior and posterior portions of the tongue edge trace.

Detection of obstruent consonant landmark for knowledge based speech recgonition system

Obstruent consonant landmarks are detected using spectral energy difference profiles. This study expands upon previous work by Liu. A[J. Acoust. Soc. Am. 100, 3417-3430, 1996]. The proposed algorithm detects four types of landmarks : [stop closure], [stop release], [fricative closure] and [fricative release], where affricates are detected by combining [stop closure], [fricative closure] and [fricative release]. In addition to finding abrupt changes in energy differences, we use energy contours, relative energy and spectral center of gravity differences. This method results in improved performance particularly for CV obstruents. Overall detection rates for stop closure and release are 76.9% and 85.7% for obstruent landmarks in TIMIT, and fricatives yield 82.2% and 83.6% respectively. For strident fricatives, the figures are 94.7% and 93.6%.

Computer simulations of intraoral pressure patterns during voiced stop consonant production

Several past studies have used laryngeal and/or upper vocal tract models to explore aerodynamic control during production of obstruent consonants, yet many aspects of such control remain unclear. Of particular interest in this work is how varying laryngeal and vocal tract dimensions such as occur among men, women, and children influence phonatory behavior and the time course of intraoral pressure (Pio) increase during voiced stop consonant production. To maintain phonation during a voiced stop closure, Pio must remain below the subglottal pressure. Physiological and modeling studies indicate that adult speakers actively increase supraglottal volumes during voiced stops, which slows the rate of Pio increase. Speakers with smaller vocal tracts may either be less successful in slowing the rate of Pio buildup, or else may perform more extreme volumetric changes to achieve similar end results. The current study uses data recently collected on voicing and Pio during stop production in men, women, and children. ...

The role of tongue articulation for /s/ and /z/ production in whispered speech

Although the timing of the initiation and cessation of vocal fold vibrations is crucial to characterize the voiced and voiceless cognates, other cues, such as the duration of preceding vowels, the patterns of the formant transitions in the following vowels, and the period of stop closure, may also play important roles in performing these distinctions. The present study is to further investigate the role of tongue articulatory movements during voiced and unvoiced consonant production, specifically when the vocal folds do not vibrate during the production of fricative consonants, /s/ and /z/ in whispered speech. A normal Japanese speaker served as the subject. The palato-lingual contact patterns during the intervocalic consonant /s/ and /z/ in whispered speech were recoded using dynamic electro-palatography. The results show that the area of palato-lingual contact is clearly wider during /z/ production than /s/ production; the opening for fricative turbulent noise production is narrower and longer for /z/ than for /s/. In addition, the contact pattern is unstable for /s/ production.

Effect of bilateral stimulation of the subthalamic nucleus on different speech subsystems in patients with Parkinson's disease

The effect of deep brain stimulation on the two speech‐production subsystems, articulation and phonation, of nine Parkinsonian patients is examined. Production parameters (stop closure voicing; stop closure, VOT, vowel) in fast syllable‐repetitions were defined and measured and quantitative, objective metrics of vocal fold function were obtained during vowel production. Speech material was recorded for patients (with and without stimulation) and for a reference group of healthy control speakers. With stimulation, precision of the glottal and supraglottal articulation as well as the phonatory function is reduced for some individuals, whereas for other individuals an improvement is observed. Importantly, the improvement or deterioration is determined not only on the basis of the direction of parameter change but also on the individuals' position relative to the healthy control data. This study also notes differences within an individual in the effects of stimulation on the two speech subsystems. These findings qualify the value of global statements about the effect of neurostimulatory operations on Parkinsonian patients. They also underline the importance of careful consideration of individual differences in the effect of deep brain stimulation on different speech subsystems.

Production of Parisian stops word‐initial stops in the vicinity of a voiceless stop

This study examines how French speakers produced stop voicing contrasts in the sentence répète CVC tout‐de‐suite. Durations (sentence, vowel before and after word‐initial stops, closure voicing, VOT) and number of produced stop closures (/t/, /C/) were collected. There was a strong positive correlation between speaker’s sentence durations and number of closure produced: Rapid speakers produced mostly one closure, whereas slow speakers generally produced two closures. One‐closure and two‐closure productions were separately analyzed. In the two‐closure productions, significant (longer voicing in the /t/ closure in anticipation of /bdg/ than /ptk/, longer closure voicing for /bdg/ than for /ptk/, longer vowel duration following /bdg/ than /ptk/) and nonsignificant voicing‐related duration differences (e.g., closure) were found. Unlike in the two‐closure productions, average closure duration was significantly longer before /ptk/ than before /bdg/, while there was no significant voicing‐conditioned effect of the word‐initial stop on the duration of the following vowel in the one‐closure productions. As in the two‐closure productions, average closure voicing duration remained significantly longer before /bdg/ than before /ptk/. Findings suggest that closure voicing remains the most salient cue to the voicing distinction irrespective of contextual and speaking rate variations.

Individual differences in the production and perception of the voicing contrast by native and non-native speakers of English

Investigations of acoustic characteristics of speech production and their perceptual correlates often determine that various common patterns are observed among groups of talkers/listeners. It is also sometimes reported that a certain amount of noise occurred in the data, i.e., that not all subjects fit general patterns that were observed. While individuals who do not demonstrate typical patterns are often viewed as outliers, subjects who represent exceptions also provide important information. The present study reports findings obtained from 15 native speakers of English and 15 non-native (native Mandarin) speakers of English who were recorded producing several final-position voiced/voiceless CVC word pairs and who also made voicing judgments about voiced/voiceless cognates produced by other native English and native Mandarin speakers. All native subjects in the present study produced multiple acoustic cues in making voicing distinctions (e.g., vowel duration, final stop closure duration, voicing during final stop occlusion, release burst); however, not all subjects used all these acoustic cues or the same combinations of cues in their voicing contrasts. Only about half the native Mandarin speakers used multiple acoustic cues in attempting to produce a voicing contrast. Various group trends, as well as subgroup variations, in production and perception will be discussed.

Variable Perception of White Noise in Ambiguous Phonetic Contexts: The Case of /p/ and /f/

The roles of spectro-temporal coherence, lexical status, and word position in the perception of speech in acoustic signals containing a mixture of speech and nonspeech sounds were investigated. Stimuli consisted of nine (non)words in which either white noise was inserted only into the silent interval preceding and/or following the onset of vocalic transitions ambiguous between /p/ and /f/, or in which white noise overlaid the entire utterance. Ten listeners perceived 85% /f/s when noise was inserted only into the silent interval signaling a stop closure, 47% /f/s when noise overlaid the entire (non)words, and 1% in the control condition that contained no noise. Effects of spectro-temporal coherence seemed to have dominated perceptual outcomes, although the lexical status and position of the critical phoneme also appeared to affect responses. The results are explained more adequately by the theory of Auditory Scene Analysis than by the Motor Theory of Speech Perception.

Phonetic vs. Phonological Lengthening in Affricates

Affricate consonants consist of two portions: stop closure and frication. Can these portions play different roles in phonetic and phonological processes? In this study, I address the question by probing the behavior of Hungarian affricates under lengthening. I measure the duration changes that affricates undergo in two types of lengthening processes: first, a phonetic process of final lengthening and second, a phonological process of gemination. I show that these two processes alter the internal structure of affricates in very different ways. The results suggest that the difference between phonetic and phonological processes is in fact deeper than a mere difference between “gradient” and “categorical” effects.

The behavior of affricates under restricted lengthening conditions

This study uses affricates as a test case for lengthening processes in speech. In general, consonants can lengthen as the result of phonological factors, such as a geminating suffix, or as the result of phonetic factors such as position within a phrase (Keating et al. 2003, Byrd et al. 2000, 2005). In Hungarian and many other languages, however, the presence of an additional consonant restricts phonological lengthening because CCC clusters containing geminates are ill‐formed (Kenesei et al. 1998). Acoustic duration measurements were used to examine whether this restriction also holds for phonetic lengthening. Initial results from three male Hungarian speakers indicate that it does not. Consonants in phrase‐final position are significantly longer than their counterparts in phrase‐medial position, whether they stand alone or in a cluster. A focus on lengthened affricates, however, reveals that the ‘‘shape’’ of lengthening differs in these two conditions. Affricates in the stand‐alone condition lengthen in a lopsided fashion, showing increases primarily in frication duration; those in the cluster condition lengthen more symmetrically, with increases in both stop closure and frication durations. These findings provide new support for the idea that affricates possess different structures at different levels of analysis (Lombardi 1990, Clements 1999).

Interpolation of vocal-tract shape during stop closures from transition segments in vowel-consonant-vowel syllables

Children with prelingual profound hearing impairment have great difficulty in acquiring speech. Speech-training systems providing visual feedback of vocal-tract shape are found to be useful for improving vowel articulation. Vocal-tract shape estimation, based on LPC and other analysis techniques, generally fails during stop closures, and this restricts its effectiveness in speech training for production of consonants not having visible articulatory efforts. A technique based on two-dimensional surface modeling of the area values, estimated by LPC analysis, during the vowel-consonant and consonant-vowel transitions preceding and following the stop closure, has been investigated for interpolating the area values during the stop closures. Surface modeling was based on least-squares bivariate polynomials and Delaunay triangulation methods. Syllables of the type /aCa/, /aCi/, /iCa/, /iCi/, and /uCu/ with stop consonants /p/, /b/, /t/, /d/, /k/, and /g/ were analyzed for the estimation of place of stop closure. For bilabial, alveolar, and velar stops, the place could be estimated consistently with conic polynomial surface interpolation. Estimation of place, based on Delaunay surfaces, was consistent for bilabial and velar stops. However, cubic polynomial surface interpolation results were less consistent in estimating the place of constriction.

Relationships between the intelligibility and acoustic properties of native English and Mandarin-accented English

Studies examining effects of talkers’ and listeners’ linguistic backgrounds on speech intelligibility have produced mixed results, and relatively little is known about which acoustic-phonetic features of native and non-native speech are responsible for many findings. These issues are addressed here via investigation of how acoustic properties of final consonant voicing contrasts influence word intelligibility. Native English and native Mandarin talkers’ productions of English words were presented in isolation to native English and native Mandarin listeners in an identification task. Intelligibility findings were related to preceding vowel duration, stop consonant duration, burst duration, and proportion of voicing during stop closure. As expected, native English listeners were more accurate identifying words spoken by native than non-native talkers. In contrast to previous findings of an interlanguage speech intelligibility benefit (ISIB) for sentences, non-native listeners found native speech more intelligible than non-native speech. However, non-native listeners found non-native speech more intelligible than did native listeners. For native talkers, all four acoustic measures contributed significantly to correct identification of voicing contrasts by both native and non-native listeners (with closure voicing most salient). In contrast, for non-native talkers, listeners tended to rely primarily on closure voicing and burst duration. Ramifications for ISIB will be discussed.

Production and perception of place of articulation errors

Using ultrasound to examine speech production is gaining popularity because of its portability and noninvasiveness. This study examines ultrasound recordings of speech errors. In experiment 1, ultrasound images of participants’ tongues were recorded while they read tongue twisters. Onset stop closures were measured using the angle of the tongue blade and elevation of the tongue dorsum. Measurements of tongue twisters were compared to baseline production measures to examine the ways in which erroneous productions differ from normal productions. It was found that an error could create normal productions of the other category (categorical errors) or abnormal productions that fell outside the normal categories (gradient errors). Consonant productions extracted from experiment 1 were presented auditory-only to naive listeners in experiment 2 for identification of the onset consonant. Overwhelmingly, the participants heard normal productions and gradient error productions as the intended sound. Categorical error productions were judged to be different from the intended sound. The only effect of erroneous production on perception appears to be a slight increase in reaction time, which may suggest that error tokens are abnormal in some way not measured in this study.