VCV Sequence Research Articles

Hearing tongue loops: Perceptual sensitivity to acoustic signatures of articulatory dynamics

Previous work has shown that velar stops are produced with a forward movement during closure, forming a forward (anterior) loop for a VCV sequence, when the preceding vowels are back or mid. Are listeners aware of this aspect of articulatory dynamics? The current study used articulatory synthesis to examine how such kinematic patterns are reflected in the acoustics, and whether those acoustic patterns elicit different goodness ratings. In Experiment I, the size and direction of loops was modulated in articulatory synthesis. The resulting stimuli were presented to listeners for a naturalness judgment. Results show that listeners rate forward loops as more natural than backward loops, in agreement with typical productions. Acoustic analysis of the synthetic stimuli shows that forward loops exhibit shorter and shallower VC transitions than CV transitions. In Experiment II, three acoustic parameters were employed incorporating F3-F2 distance, transition slope, and transition length to systematically modulate the magnitude of VC and CV transitions. Listeners rated the naturalness in accord with those of Experiment I. This study reveals that there is sufficient information in the acoustic signature of "velar loops" to affect perceptual preference. Similarity to typical productions seemed to determine preferences, not acoustic distinctiveness.

The ‘Trough Effect’: an Ultrasound Study

Bilabial stops often show a lowering of the tongue in symmetrical VCVsequences. The causes of this phenomenon, sometimes called the ‘trough effect’,are unknown. However, it could have important implications for the study of timevaryingaspects of speech events. Ultrasound is a non-invasive technique that hasallowed us to image the shape of the tongue in real time and measure the actualtongue displacement that occurs in the C of a VCV sequence. Five repetitions ofsymmetrical V<inf>1</inf>CV<inf>2</inf> sequences with the bilabial stops /b, p/ were obtained from 10British English speakers. Results showed not only differences in the direction anddegree of the tongue displacement but also differences in the tongue contour configurationbetween subjects. This study demonstrates the effectiveness of ultrasoundas a technique in phonetic research, making possible the analysis of tonguesurface movement for large amounts of data from multiple subjects.

Measures of articulatory variability in VCV sequences

Functional data analysis is used to examine articulatory variability across repetitions in normal speech, under different movement constraints. A temporal normalization technique is applied to align trajectories of lips, jaw, and tongue in vowel-consonant-vowel sequences. Next, an index of amplitude variability is computed, defined as the mean standard deviation between peak velocities of the consonantal closure by the active articulator, in each VCV sequence. The results show that articulatory variability varies as a function of both the phonetic requirements of the consonant and the biomechanical characteristics of the articulatory structures involved.

The effect of syllabification and gemination on F2 onsets in Swedish

The quest to explain the continuousness of speech on the physical level has been dominated by the co‐production theory [Hman, J. Acoust. Soc. Am. 41 (1966)]. According to this view, the production of a VCV sequence involves a diphthongal movement from V1‐to‐V2, with a superimposed consonantal gesture. However, data from recent studies are at variance with this position—Modaressi [Ph.D. dissertation, UT Austin, 2002], Perkell [Coarticulation Strategies Speech Commun. 5, 47–68 (1986)]. These studies document a trough‐phenomena, which suggests a discontinuity in muscular activity during the production of the consonant. This paper provides additional acoustic evidence in support of sequential programming of consonant‐vowel events as advocated by Joos [Acoustic Phonetics Lang. 24 (1948)]. It examines symmetrical VCV sequences in Swedish natural speech with syllable boundaries and duration of consonant gemination altered to produce different types of temporal interval between V1 and V2; i.e., V♯CV, VCC♯V, VC♯CV, VCC♯CV. F2 of V1mid, V1offset, V2onset, and V2mid were measured. Locus equations were plotted for all VC contacts. Statistical analysis of these data show: (1) de‐activation of tongue movement at the CV boundary, (2) a reduction of the influence of V1 on V2 as a function of increasing consonant duration, and (3) a weak degree of CV coarticulation.

Correlations between vowel and the subsegments of an obstruent in CV and VCV sequences

It is well known that there is a significant negative correlation between a consonant and the preceding or following vowel. However, it has seldom been specified what relationship lies between the subsegments (closure, frication, and aspiration) of an obstruent and the preceding or following vowel in Korean. This work investigates the relationship between the vowel and the subsegments of a Korean coronal obstruent in CV and VCV sequences. There was a significant negative correlation between the gap and vowel (r=−0.900) in utterance initial CV sequence but no significant correlation between frication and vowel. On the other hand, there was a significant negative correlation between the preceding vowel and closure (r=−0.510) in the VCV sequence but no significant correlation between the preceding vowel and other subsegments. There was a significant negative correlation between the following vowel and gap (r=−0.545) but no significant correlation between the following vowel and other subsegments. Generally, there was a significant correlation between the vowel and an immediately adjacent segment than between the vowel and remote segments. Correlation was stronger in the CV sequence than in the VCV sequence for the same pair of variables. Speech Communication Best Student Paper Award.

The effect of stress on F2 onsets in VCV utterances

This study compares a superposition or vowel-to-vowel theoretical framework versus a segment-by-segment account to best account for the coarticulatory dynamics of VCV utterences. The ‘‘trough effect,’’ a deactivation of tongue musculature after the initial vowel of a symmetrical VCV sequence (e.g., /ibi/), is not readily explainable by traditional co-production (vowel-to-vowel) accounts of coarticulation. A Jossian segment-by-segment programming sequence appears to be more compatible with ‘‘deactivation’’ phenomena. One way to manipulate extent of ‘‘deactivation’’ is to impose differential degrees of syllable stress on either side of the stop consonant. Locus equations can provide an acoustic window on this question as timing differences should show up as slope/intercept variations. Emphatic stress on V1 is expected to lessen deactivation relative to weak V1 stress, and consequently greater levels of anticipatory coarticulation should occur, resulting in higher locus equation slopes. Four different stress-vowel conditions were used: weak versus emphatic stress counterbalanced over V1 and V2. There were five vowel contexts for V1 and ten vowel contexts for V2, surrounding the three voiced stop consonants /b, d, g/. Results will be reported on three speakers of American English. [Work supported by NIH.]

Interarticulator phasing, locus equations, and degree of coarticulation.

A locus equation plots the frequency of the second formant at vowel onset against the target frequency of the same formant for the vowel in a consonant-vowel sequence, across different vowel contexts. It has generally been assumed that the slope of the locus equation reflects the degree of coarticulation between the consonant and the vowel, with a steeper slope showing more coarticulation. This study examined the articulatory basis for this assumption. Four subjects participated and produced VCV sequences of the consonants /b, d, g/ and the vowels /i, a, u/. The movements of the tongue and the lips were recorded using a magnetometer system. One articulatory measure was the temporal phasing between the onset of the lip closing movement for the bilabial consonant and the onset of the tongue movement from the first to the second vowel in a VCV sequence. A second measure was the magnitude of the tongue movement during the oral stop closure, averaged across four receivers on the tongue. A third measure was the magnitude of the tongue movement from the onset of the second vowel to the tongue position for that vowel. When compared with the corresponding locus equations, no measure showed any support for the assumption that the slope serves as an index of the degree of coarticulation between the consonant and the vowel.

The effect of speaking rate on lingual behavior for a transconsonantal vocalic gesture: An x-ray microbeam study

The purpose of the present study was to further explore the relationship between speaking rate and articulatory movements. A good deal of evidence suggests that speaking rate variation is accompanied by changes in the extent of overlap for successive articulatory gestures, however, previous work has shown that a simple model of gestural sliding is inadequate to explain changes in acoustic measures across speaking rates [Weismer et al. (in submission)]. Therefore, a more descriptive study of movement may be one step toward developing an acoustic model of changes in articulatory processes across speaking rate. Exploration of lingual movement across speaking rate was carried out using data from the x-ray microbeam data base. Ten speakers produced multiple tokens of the sentence ‘‘The other one is too big’’ at different speaking rates. Plots of the changing tongue contour through the VCV sequence /ubI/ from ‘‘too big’’ were examined to determine if the pattern of tongue movement was similar across speaking rates but with more or less overlap, or if the behaviors looked qualitatively different. Preliminary results show at least two different variations in lingual movement underlying changes in speaking rate. [Work supported by DC00820 and DC00319.]

The contact index method of electropalatographic data reduction

This paper presents a new method of electropalatographic data reduction, namely, the contact index method. It provides accurate information about the distribution and size of linguopalatal contact based on values for an anteriority index, a posteriority index and a centrality index. These values are calculated using coefficients specific to each row of electrodes along the sagittal dimension and to each column of electrodes along the coronal dimension. The contact index method is applied to the analysis of two research topics: V-to-C coarticulation effects at the palatal zone for consonants differing in place and manner of articulation characteristics; and intraconsonantal variability across repetitions of a given VCV sequence. Results are evaluated in the light of the theory of speech production.

Tongue Body Kinematics in Velar Stop Production: Influences of Consonant Voicing and Vowel Context

This study examines vertical and horizontal tongue body movements in VCV sequences, where the consonant is a voiced or voiceless velar stop. The movement data were recorded using a magnetic transduction technique in two subjects. Consistent with studies of lip and jaw kinematics, the duration of the tongue body raising movement towards closure for the consonant was longer for the voiced stop. In contrast to lip and jaw movements, peak velocity and amplitude of the raising movements were consistently higher for the voiced stop. The larger displacement of the closing movement for the voiced stop was due to a lower starting position of the movement during the preceding vowel. Examination of the tongue body lowering movement for the vowel preceding the velar stop showed it to be longer when the following stop was voiced. Also this lowering movement had a higher peak velocity and amplitude in the voiced environment. These results thus suggest that both the lowering and raising movements in the VC sequence are affected by the voicing status of the consonant. In addition, the second vowel in the VCV sequence showed reliable influences on tongue body movements for the first vowel and the consonant.

Characteristics of articulatory coordination during Japanese VCV sequences: Observations using optical and marker-tracking systems.

We examined the influence of context on the articulatory positions of the tongue, lips, and mandible using optical and marker-tracking systems and speculated articulatory coordination during the production of Japanese VCV sequence from the standpoint of current theories of speech production. The primary articulator for the consonant was comparatively invariant in the context. The secondary articulator was variant in the context. Influence of the preceding vowel on the secondary articulators for the con-sonant decreased monotonically and the influence of the following vowel increased in the same way. Thus, movements during the Japanese VCV sequence seem to consist of basic vowel-to-vowel gestures and comparatively invariant movement for the relevant consonant articulator.

Consonant discrimination using the formant coarticulation model

Formant trajectories in the vicinity of consonants in continuous speech are observed to discriminate the place of articulation of the consonants. The coarticulation model [S. Chiba, Proc. IEEE ICASSP‐86, Paper 49‐10 (1986)] with a target formant frequency for consonants is developed based on the observation of the formant trajetories in natural VCV utterances. The coarticulation model proposed here is as follows: Fb − Ft = a(Fp − Ft) + b(Fe − Ft) + c(Ff − Ft) + E, where Fb, Fp, Fe, and Ff are the second formant frequencies at the centers and the consonant boundaries of the initial and final vowel segments in a VCV sequence, Ft is the target second formant frequency of the consonant, and E is the estimation error. The parameter values of a, b, c, and Ft are estimated by the method of least squares using actual values. Three coarticulation models for labials, alveolars, and velars are estimated and these models are applied to the discrimination of place of articulation of consonants in continuous speech. Ex...

Articulatory movements in VCV sequences.

The purpose of this experiment was to study both the timing and positional properties of articulatory movements in VCV utterances. Conventional cinefluorographic techniques were used to track the movements of the upper lip, lower lip, jaw, tongue tip, and tongue body of two speakers who read randomized lists of VCV utterances containing the vowels /i,a,u/ and the consonants /p,t,k/, in all possible combinations. Results showed that the timing of articulatory movements in a VCV sequence are constrained by the intervocalic consonant, even if the gesture for the consonant is not a contradictory one. Anticipatory movements toward the second vowel always begin during the closure period of the intervocalic consonant. The appearance of carry over coarticulation effects depends on the phonetic identity of the particular segment or degree of involvement of the articulator. Carry over effects, like anticipatory effects, did not extend beyond an immediately adjacent segment. These findings suggest that the rules governing the segmental input to a speech string might be simpler than present models suggest.

On the perception of coarticulation effects in English VCV syllables.

Ohman’s 1966 investigation of the acoustic correlates of coarticulation in VCV sequences indicates that terminal formant frequency transition values are strongly influenced by the nature of the transconsonantal vowel. This experiment was designed to explore the perceptual correlates of Ohman’s spectrographic findings. We discovered that when a VCV sequence (where C is a voiceless plosive) is cut in two during the period of consonantal closure, there are not enough remaining cues in either the resulting VC or CV sequences to allow for identification of the deleted segment or of its articulatory features. However, it appears that coarticulation effects may hinder recognition of nonfinal allophones placed artificially in final position. Consonants in VC sequences spliced from original VCV utterances are more difficult to identify than unreleased final consonants of the same quality.

Perception of Coarticulation in English VCV Sequences

Öhman's 1966 investigation of the acoustic correlates of coarticulation in Swedish and English VCV sequences [J. Acoust. Soc. Amer. 39, 151–168 (1966)] indicates that terminal formant transition frequency values are strongly influenced by the nature of the transconsonantal vowel. However, the literature reflects no attempts to discover whether these coarticulation effects are perceptible, e.g., whether in a VCV sequence the initial VC carries significant perceptual cues as to the quality of the following V. The present experiment was designed to investigate the latter question. Forty-eight VCV utterances involving the vowels /i æ a u/ and the consonants /p t k/ were recorded and either the initial or final vowel removed by splicing techniques. The resulting tapes were played to listeners who were asked to indicate which vowel had been deleted. Results were random indicating that coarticulation effects are not sufficient cues to the perception of the vowels which occasion them. These results are counterevidence for the claim by Wickelgren [Psychol. Rev. 76, No. 1, 1–15 (1969)] that the “context sensitive” allophone may be a basic cue in speech recognition. The results also suggest that some coarticulation effects may not have to be taken into consideration in speech synthesis.