Consonant Release Research Articles

Preservation of second formant transitions during simultaneous communication:: A locus equation perspective

This study investigated the preservation of second formant transition acoustic cues to intelligibility in speech produced during simultaneous communication (SC) from a locus equation perspective. Twelve normal hearing, experienced sign language users were recorded under SC and speech alone (SA) conditions speaking a set of sentences containing monosyllabic words designed for measurement of second formant frequencies in consonant–vowel–consonant (CVC) syllables. Linear regression fits made to coordinates representing second formant transition onset and offset frequencies following stop consonant release of CVC syllables (locus equations) were used to examine place of articulation cues in both SA and SC conditions. Although results indicated longer sentence durations for SC than SA, locus equation slopes and intercepts obtained from speech produced during SC were virtually identical to those obtained during SA, indicating no degradation of stop consonant acoustic cues during SC. This conclusion is consistent with previous research indicating that temporal alterations produced by SC do not involve violations of other rules of spoken English. Educational objectives: As a result of this activity, the participant will be able to (1) describe SC; (2) explain the role of SC in communication with children who are deaf; (3) describe second formant transitions in English speech; and (4) identify second formant transition patterns in speech produced during SC.

Modeling stop-consonant releases for synthesis

This study is part of a project leading to rule-based speech synthesis using the HLsyn synthesizer. In HLsyn, stop-consonant releases are generated by controlling the time variation of a constriction that is formed by the lips, the tongue blade, or the tongue body. In order to generate a consonant release that is perceptually acceptable and that has acoustic characteristics that match those of normal speech, it was found that the trajectory of the consonant release (cross-sectional area versus time) had to exhibit an initial rapid rise, followed by a delay in which the rise was interrupted, followed finally by a final rise. The burst at the consonant release is generated by the airflow through the constriction during the time that the rise is delayed. A model of the time course of this three-stage release of the articulator has been developed, taking into account the role of the intraoral pressure, the tapering formed by the articulator, and the glottal area. The model shows that the delay between the initial and final area increases is progressively longer for labials, alveolars, and velars, in agreement with acoustic data on the burst duration. [Work supported in part by NIH Grant Nos. MH52358 and DC00075.]

Coarticulation in CV syllables: a comparison of Locus Equation and EPG data

Using electropalatographic (EPG) data, the following hypothesis is tested: the slope value generated by a locus equation (LE) analysis of the F 2 transition in CV syllables is an accurate reflection of the degree of coarticulation between the consonant and the vowel in that syllable. The consonants studied are /∂ z z d g n n l r/. Comparisons between EPG and LE data suggest that the LE analysis provides an accurate reflection of the degree of coarticulation for the stop and nasal classes in English, which have an alveolar and a velar place of articulation amongst the lingual consonants. By contrast, the correlation between EPG and LE data for the fricative consonants is very poor. Two explanations are offered for the poorer results for the fricatives: (1) the fricative noise following consonant release obscures the F 2 transition, rendering formant measurement less accurate, and (2) the LE is capable of encoding gross differences in degree of coarticulation (such as that between an alveolar and a velar) but not more subtle differences such as those between the various coronal articulations.

Coarticulation Resistance of American English Consonants and its Effects on Transconsonantal Vowel-to-Vowel Coarticulation

We explored the variation in the resistance that lingual and non lingual consonants exhibit to coarticulation by following vowels in the schwa+CV disyllables of two native speakers of English. Generally, lingual consonants other than /g/ were more resistant tho coarticulation than thhe liabial consonants /b/ and /v/. Coarticulation resistance in the consonant also affected articulatory evidence for trans consonantal vowel-to-vowel coarticulation, but did not show consistent acoustic effects. As for effects of coarticulation resistance in thhe following vowel, articulatory and acoustic effects were quite liarge at consonantre lease but much weaker farther into the following stressed vowel. Correlations between coarticulation resistance effects at consonantrelease and liocus equation slopes were highly significant, consistent with the view that variation in coarticulation resistance explains differences among consonants in liocus equation slopes.

Temporal encoding of the voice onset time phonetic parameter by field potentials recorded directly from human auditory cortex.

Voice onset time (VOT) is an important parameter of speech that denotes the time interval between consonant onset and the onset of low-frequency periodicity generated by rhythmic vocal cord vibration. Voiced stop consonants (/b/, /g/, and /d/) in syllable initial position are characterized by short VOTs, whereas unvoiced stop consonants (/p/, /k/, and t/) contain prolonged VOTs. As the VOT is increased in incremental steps, perception rapidly changes from a voiced stop consonant to an unvoiced consonant at an interval of 20-40 ms. This abrupt change in consonant identification is an example of categorical speech perception and is a central feature of phonetic discrimination. This study tested the hypothesis that VOT is represented within auditory cortex by transient responses time-locked to consonant and voicing onset. Auditory evoked potentials (AEPs) elicited by stop consonant-vowel (CV) syllables were recorded directly from Heschl's gyrus, the planum temporale, and the superior temporal gyrus in three patients undergoing evaluation for surgical remediation of medically intractable epilepsy. Voiced CV syllables elicited a triphasic sequence of field potentials within Heschl's gyrus. AEPs evoked by unvoiced CV syllables contained additional response components time-locked to voicing onset. Syllables with a VOT of 40, 60, or 80 ms evoked components time-locked to consonant release and voicing onset. In contrast, the syllable with a VOT of 20 ms evoked a markedly diminished response to voicing onset and elicited an AEP very similar in morphology to that evoked by the syllable with a 0-ms VOT. Similar response features were observed in the AEPs evoked by click trains. In this case, there was a marked decrease in amplitude of the transient response to the second click in trains with interpulse intervals of 20-25 ms. Speech-evoked AEPs recorded from the posterior superior temporal gyrus lateral to Heschl's gyrus displayed comparable response features, whereas field potentials recorded from three locations in the planum temporale did not contain components time-locked to voicing onset. This study demonstrates that VOT at least partially is represented in primary and specific secondary auditory cortical fields by synchronized activity time-locked to consonant release and voicing onset. Furthermore, AEPs exhibit features that may facilitate categorical perception of stop consonants, and these response patterns appear to be based on temporal processing limitations within auditory cortex. Demonstrations of similar speech-evoked response patterns in animals support a role for these experimental models in clarifying selected features of speech encoding.

Speaking-rate-induced variability in F2 trajectories.

This study examined speaking-rate-induced spectral and temporal variability of F2 formant trajectories for target words produced in a carrier phrase at speaking rates ranging from fast to slow. F2 onset frequency measured at the first glottal pulse following the stop consonant release in target words was used to quantify the extent to which adjacent consonantal and vocalic gestures overlapped; F2 target frequency was operationally defined as the first occurrence of a frequency minimum or maximum following F2 onset frequency. Regression analyses indicated 70% of functions relating F2 onset and vowel duration were statistically significant. The strength of the effect was variable, however, and the direction of significant functions often differed from that predicted by a simple model of overlapping, sliding gestures. Results of a partial correlation analysis examining interrelationships among F2 onset, F2 target frequency, and vowel duration across the speaking rate range indicated that covariation of F2 target with vowel duration may obscure the relationship between F2 onset and vowel duration across rate. The results further suggested that a sliding based model of acoustic variability associated with speaking rate change only partially accounts for the present data, and that such a view accounts for some speakers' data better than others.

Modeling and synthesis of the lateral consonant /l/

The lateral consonant in English is generally produced with a backed tongue body, a midline closure of the tongue blade at the alveolar ridge, and a path around one or both of the lateral edges of the tongue blade. In prevocalic lateral consonants, the release of the closure causes a discontinuity in the spectral characteristics of the sound. Past attempts to synthesize syllable-initial lateral consonants using formant changes alone to represent the discontinuity have not been entirely satisfactory. Data from prior research has shown rapid changes in not only the formant frequencies but also in the glottal source amplitude and spectrum and in the amplitudes of the formant peaks at the consonant release. Further measurements have been made on additional utterances, guided by models of lateral production. Based on these data, new synthesis attempts have incorporated changes in source amplitudes, formant bandwidths, and the location of a pole-zero pair. Including these additional parameters improves the naturalness of the synthesized lateral-vowel syllables in initial perception tests. Results of listening tests indicating the relative importance of the various factors to the naturalness of the synthesized syllables will be reported. [Work supported in part by a LeBel Fellowship and by NIH Grant No. DC00075.]

On the relevance of locus equations for production and perception of stop consonants.

We examined the possible relevance of locus equations to human production and perception of stop consonants. The orderly output constraint (OOC) of Sussman, Fruchter, and Cable (1995) claims that humans have evolved to produce speech such that F2 at consonant release and F2 at vowel midpoint are linearly related for consonants so that developing perceptual systems can form representations in an F2ons-by-F2vowel space. The theory claims that this relationship described by locus equations can distinguish consonants, and that the linearity of locus equations is captured in neural representations and is thus perceptually relevant. We investigated these claims by testing how closely locus equations reflect the production and perception of stop consonants. In Experiment 1, we induced speakers to change their locus equation slope and intercept parameters systematically, but found that consonants remained distinctive in slope-by-intercept space. In Experiment 2, we presented stop-consonant syllables with their bursts removed to listeners, and compared their classification error matrices with the predictions of a model using locus equation prototypes and with those of an exemplar-based model that uses F2ons and F2vowel, but not locus equations. Both models failed to account for a large proportion of the variance in listeners' responses; the locus equation model was no better in its predictions than the exemplar model. These findings are discussed in the context of the OOC.

Interarticulator programming in VCV sequences

This study examined the coordination of tongue body and lip movements in VCV sequences, where the consonant is a bilabial stop /p, b/, and the vowel one of /i, a, u/; only asymmetrical vowel contexts were analyzed. Lip and tongue timing and vowel-to-vowel tongue body kinematics were examined. The movements were recorded using a magnetometer system. Four subjects participated and produced ten tokens of each sequence. The phasing between the onset of the lip closing movement and the onset of the tongue body movement from the first to the second vowel varied across subjects, with no obvious pattern according to consonant voicing or vowel context. Overall, the onset of the tongue movement to the second vowel started earlier relative to the lip closing movement as the length of the tongue movement trajectory increased. During the oral closure, 40%–80% of the tongue movement path was traversed, again with no clear pattern across subjects. Consonant voicing reliably influenced the tongue movement from the consonant release to the second vowel. During this interval, the tongue traversed a longer path for voiceless than for voiced stops, reflecting the longer voice onset time for the voiceless stops. [Work supported by NIH.]

Analysis of F2 transitions in the speech of stutterers and nonstutterers

Lingual coarticulation was acoustically examined in the fluent speech of stutterers and nonstutterers. Coarticulation was evaluated by determining the slope of second formant (F2) transitions following consonant release. In general, stutterers were found to display larger slope coefficients in comparison to the nonstutterers. The large coefficients were interpreted to reflect greater or quicker dimensional changes in vocal-tract behavior compared to those of nonstutterers. Discussion focuses on the speech motor skills characterizing fluent speech production.

A note on prespeech and early speech coarticulation

Development of consonant + vowel (CV) coarticulation was examined acoustically in two normally developing children. Data of the vocalizations from each child at 11 mos and 20 mos of age were collected. These vocalizations corresponded to prespeech and early speech periods of linguistic development, respectively. A specific CV form, common in each child's prespeech and early speech vocalizations, was selected for analysis. Coarticulation was evaluated by determining the slope of formant 1 (Fl) and formant 2 (F2) transitions following consonant release. The formant transition slopes were found to be “shallower” at 20 mos of age compared to the 11 mos period with the largest developmental change occurring for F1 transitions. Discussion focuses on the intrasyllabic coarticulatory effects characterizing prespeech and early speech development.

Relearning consonant timing: Evidence from English and Russian

Advocates of the gestural approach to phonetic or phonological representations argue that degree of overlap between articulatory gestures can account for many phonetic regularities (such as assimilation, deletion, or release of consonants in clusters) that can contribute to the perception of a ‘‘foreign accent’’ [C. P. Browman and L. Goldstein, Phonetica 49, 155–180 (1992); E. C. Zsiga, GURT 1995, pp. 575–587 (1995)]. The research reported here compares patterns of consonant overlap at word boundaries in English and Russian, and investigates the extent to which adult language learners transfer the timing patterns of their native language to the second language. Native Russian speakers learning English and native English speakers learning Russian produced phrases in English and Russian contrasting VC♯CV, VC♯V, and V♯CV sequences, with varying stress patterns and syntactic configurations. The ratio of closure duration in clusters as compared with single consonants [E. C. Zsiga, J. Phon. 22, 121–140 (1994)] is examined, in order to determine patterns of consonant timing in the two languages (including effects of stress and boundary strength) and to elucidate the extent to which the timing patterns of second-language speakers resemble that of native speakers.

Perceiving oral release rate of voiced stop consonants

Because of the differences in articulator mass and contact length, initial rates of increase in a constriction area at a consonant release may differ for stops produced at the various places of articulation. This paper examines the listener preferences for variations in the oral release rate (ORR) of syllable-initial labial, alveolar, and velar voiced stops. For each place of articulation, a five-member ORR continuum was synthesized using a set of articulatory parameters [K. N. Stevens and C. A. Bickley, J. Phon. 19, 161–174 (1991)] to control the rate of increase in the oral cross-sectional area at the stop release. ORRs were 15, 20, 30, 50, and 100 cm2/s for [b] and [d], and 10, 15, 20, 30, and 50 cm2/s for [g]. The synthesized CV syllables were presented in pairs to naive and experienced listeners for preference judgments. In general, faster ORRs were preferred for labial stops than for alveolar and velar stops. For the most stimuli, experienced listeners showed clearer preferences than did naive listeners. Normalized scores indicated that the range of preferred ORRs for alveolars was narrower than for labials and velars. Implications of these results for studies of phonetic prototypes will be discussed. [Work supported by NIH.]

Consonant release and the syllable

L'A. presente quelques regles phonologiques considerees comme les plus explicatives du role de la syllabe. Il discute ensuite le phenomene phonetique d'emission des consonnes et examine les roles que peut jouer le trait non-emission en phonologie dans le but de montrer que ce trait est plus explicatif que la notion de syllabe. Il explique ainsi la nasalisation des occlusives en francais quebecois et la desonorisation en allemand

Attributes of lateral consonants

This paper attempts to define acoustic properties of laterals in English that are adjacent to vowels and in syllabic nuclei. When the tongue is in the lateral configuration, there is an increased bandwidth and decreased prominence of the second formant (due to increased losses) and some irregularities in the F3–F4 region (divided acoustic path). When a lateral consonant is produced adjacent to a vowel, there is a rapid change in the acoustic spectrum as these attributes appear or disappear. A series of acoustic analyses has investigated the nature of this discontinuity, particularly the change in amplitude and frequency of the first two spectral prominences. An abrupt change in F2 amplitude of about 10 dB at consonant release (less at closure) is a salient attribute. The attributes that distinguish a syllabic lateral and a nonlow back vowel /o/ have been examined through acoustic analyses and through perceptual experiments in which F2 bandwidth and other properties are manipulated in synthetic utterances. F2 bandwidth again appears to play a significant role in signalling this distinction. The common acoustic attributes associated with the lateral configuration appear to be used in different ways by listeners depending on the context. [Research supported in part by NIDCD.]

Transients at stop-consonant releases

The acoustic properties and perceptual significance of transients at the release of stop consonants and affricates was studied. The theory of transient production is based on a model in which pressure is built up in a closed tube and the radiated sound is calculated following an abrupt release of the pressure. Acoustic analysis of the amplitude and frequency content of transients in utterances from ten speakers was used as a guide in setting the parameters of the model. A speech synthesizer was modified to allow the generation of transients with frequency content similar to that observed in natural speech. Utterances consisting of a stop consonant or affricate followed by the vowel /a/, with various amplitudes of an initial transient, were synthesized, and listeners were asked to judge the naturalness of the stimuli. Listeners tended to prefer the presence of a transient with an amplitude approximating the measured amplitude in natural speech, although there was some variability in the responses. [Work supported in part by a grant from NIDCD.]

Underlying control strategies for the production of stop consonants

The underlying control strategies utilized in the production of stop consonants were investigated using an electromagnetic midsagittal articulometer [J. Perkell etal., J. Acoust. Soc. Am. 92, 3078–3096 (1992)]. The movements in the midsagittal plane of points on the lower jaw, lips, tongue blade, and tongue body were measured for three normal hearing, normal speaking subjects during the production of single-syllable words composed of a stop or nasal consonant followed by the vowel /ɑ / or /i/ and the consonant /t/, and spoken in a carrier phrase. Half the tokens were preceded by the fricative consonant /s/. The data show that the maximum downward velocity of the lower jaw occurs approximately at the time of the consonant release. For /sCV/ syllables, the lower jaw is held in a high position to assist in noise generation for /s/, and consequently the movement for a following labial or velar consonant follows a time course that is different from that of /CV/ syllables. The movement of the articulators during the production of these utterances at a normal speaking rate appears to have a bandwidth limitation of 5–7 Hz. [Work supported in part by grants from NIDCD.]

Models for the production and acoustics of stop consonants

Stop consonants are produced by forming a closure in the vocal tract, building up pressure in the mouth behind this closure, and releasing the closure. Models of the mechanical, aerodynamic, and acoustic events in the vicinity of the stop consonant are described, and examples of calculations of the airflow and of various components of the radiated sound are given. At the consonantal release, these components of the sound include an initial transient, a burst of frication noise, and an interval in which there is a sound source at the glottis and transitions in the formants. The models predict the absolute levels of these components for different places of articulation for the consonants.

An acoustic analysis of the effects of cue deletions on the perception of stop consonants

Cue deletion was used to examine the contribution of various acoustic cues to the identification of the English stop consonants (/b/, /d/, /g/, /p/, /t/, /k/). Stimuli were based on tokens spoken by four talkers (two men and two women) in a syllable-medial context (/(inverted vee) Cil /). Cues within five regions centered on the burst were examined: (1) the transition from the preceding vowel into consonant closure, (2) the closure interval, (3) the consonant release, (4) the initial transition from release to the following vowel, and (5) the final transition to the vowel. Each region either remained at the full normal amplitude or was attenuated fully (i.e., effectively replaced by silence). Four listeners who had normal hearing identified the 768 signals constructed from each of the possible combinations of attenuated and full-amplitude regions (i.e., 32 combinations ×6 stimuli ×4 speakers). Analyses of these identification responses demonstrates the relative importance of each region, and of each combination of regions, for consonant identification. Acoustic measures explain some aspects of the confusion errors which occurred.

Timing and magnitudes of oral and nasal flow in cochlear implant patients and normals

Vowel nasalization was assessed in cochlear implant patients pre- and post-implant, and in normal-hearing speakers, using measures of oral, nasal, and total airflow. Speech materials consisted of the utterance /taC/, (where C=/n/, /m/, or /d/, embedded in a carrier phrase. Airflow was transduced with a two-chamber Rothenberg mask. Measures included the relative timing of the onsets of nasal and oral airflow, and the ratios of peak oral and nasal flow to total flow following the /t/ release. Pre- to post-implant differences may reflect an adjustment of the control of the velum, possibly in response to a perceived difference in nasalization and/or as a consequence of concomitant changes in other speech parameters. Preliminary ratio data from one cochlear implant patient indicate a possible enhancement of the nasal/non-nasal contrast post-implant. Further, in the /tad/ utterance, the oral flow pulse at consonant release was accompanied by a small pulse of nasal flow: velar closure during the consonant may have been assisted by the oral pressure increase, thus the pressure drop at consonant release would result in a small passive velar opening movement. These observations and additional measures are being explored further. [Work supported by NIH.]