Lip kinematics in long and short stop and fricative consonants

This paper examines lip and jaw kinematics in the production of labial stop and fricative consonants where the duration of the oral closure/constriction is varied for linguistic purposes. The subjects were speakers of Japanese and Swedish, two languages that have a contrast between short and long consonants. Lip and jaw movements were recorded using a magnetometer system. Based on earlier work showing that the lips are moving at a high velocity at the oral closure, it was hypothesized that speakers could control closure/constriction duration by varying the position of a virtual target for the lips. According to this hypothesis, the peak vertical position of the lower lip during the oral closure/constriction should be higher for the long than for the short consonants. This would result in the lips staying in contact for a longer period. The results show that this is the case for the Japanese subjects and one Swedish subject who produced non-overlapping distributions of closure/ constriction duration for the two categories. However, the peak velocity of the lower lip raising movement did not differ between the two categories. Thus if the lip movements in speech are controlled by specifying a virtual target, that control must involve variations in both the position and the timing of the target.     

Vowel-related tongue movements in speech: straight or curved paths? (L)

This paper examines tongue movements between the two vowels in sequences of vowel-labial consonant-vowel, addressing the question whether the movement is a straight line or a curved path. Native speakers of Japanese and Italian served as subjects. The linguistic material consisted of words where the bilabial consonant was either long or short. The inclusion of words with different consonant lengths was motivated by earlier findings that the tongue movement is often longer when the consonant is long, which may be due to a more curved movement path. Tongue movements were recorded using a three-transmitter magnetometer system. To assess the movement path, the movement magnitude was calculated in two ways, as a straight line, the Euclidean distance, and as the actual path, obtained by summing the individual Euclidean distances between successive samples from movement onset to offset. The ratio between the path and the Euclidean distance is 1 when the movement is a straight line and greater than 1 when the path is curved. Results show that in virtually all 21 cases examined the ratio was very close to 1 and in most cases 1.2 or less. There was no reliable influence of consonant length on the ratio.     

Influences of tongue biomechanics on speech movements during the production of velar stop consonants: a modeling study

This study explores the following hypothesis: forward looping movements of the tongue that are observed in VCV sequences are due partly to the anatomical arrangement of the tongue muscles, how they are used to produce a velar closure, and how the tongue interacts with the palate during consonantal closure. The study uses an anatomically based two-dimensional biomechanical tongue model. Tissue elastic properties are accounted for in finite-element modeling, and movement is controlled by constant-rate control parameter shifts. Tongue raising and lowering movements are produced by the model mainly with the combined actions of the genioglossus, styloglossus, and hyoglossus. Simulations of V1CV2 movements were made, where C is a velar consonant and V is [a], [i], or [u]. Both vowels and consonants are specified in terms of targets, but for the consonant the target is virtual, and cannot be reached because it is beyond the surface of the palate. If V1 is the vowel [a] or [u], the resulting trajectory describes a movement that begins to loop forward before consonant closure and continues to slide along the palate during the closure. This pattern is very stable when moderate changes are made to the specification of the target consonant location and agrees with data published in the literature. If V1 is the vowel [i], looping patterns are also observed, but their orientation was quite sensitive to small changes in the location of the consonant target. These findings also agree with patterns of variability observed in measurements from human speakers, but they contradict data published by Houde [Ph.D. dissertation (1967)]. These observations support the idea that the biomechanical properties of the tongue could be the main factor responsible for the forward loops when V1 is a back vowel, regardless of whether V2 is a back vowel or a front vowel. In the [i] context it seems that additional factors have to be taken into consideration in order to explain the observations made on some speakers.     

Control of oral closure in lingual stop consonant production

Previous work has shown that the lips are moving at a high velocity when the oral closure occurs for bilabial stop consonants, resulting in tissue compression and mechanical interactions between the lips. The present experiment recorded tongue movements in four subjects during the production of velar and alveolar stop consonants to examine kinematic events before, during, and after the stop closure. The results show that, similar to the lips, the tongue is often moving at a high velocity at the onset of closure. The tongue movements were more complex, with both horizontal and vertical components. Movement velocity at closure and release were influenced by both the preceding and the following vowel. During the period of oral closure, the tongue moved through a trajectory of usually less than 1 cm; again, the magnitude of the movement was context dependent. Overall, the tongue moved in forward-backward curved paths. The results are compatible with the idea that the tongue is free to move during the closure as long as an airtight seal is maintained. A new interpretation of the curved movement paths of the tongue in speech is also proposed. This interpretation is based on the principle of cost minimization that has been successfully applied in the study of hand movements in reaching.     

Lingual kinematics and coarticulation for alveolopalatal and velar consonants in Catalan

Vertical lingual movement data for the alveolopalatal consonants /?/ and /?/ and for the dorsovelar consonant /k/ in Catalan /aCa/ sequences produced by three speakers reveal that the tongue body travels a smaller distance at a slower speed and in a longer time during the lowering period extending from the consonant into the following vowel (CV) than during the rising period extending from the preceding vowel into the consonant (VC). For two speakers, two-phase trajectories characterized by two successive velocity peaks occur more frequently during the former period than during the latter, whether associated with tongue blade and dorsum (for alveolopalatals) or with the tongue dorsum articulator alone (for velars). Greater tongue dorsum involvement for /?/ and /k/ than for /?/ accounts for a different kinematic relationship between the four articulatory phases. The lingual gesture for alveolopalatals and, less so, that for velars may exert more prominent spatial and temporal effects on V2 than on V1 which is in agreement with the salience of the C-to-V carryover component associated with these consonants according to previous coarticulation studies. These kinematic and coarticulation data may be attributed to tongue dorsum biomechanics to a large extent.     

Interarticulator programming in VCV sequences: lip and tongue movements

This study examined the temporal phasing of tongue and lip movements in vowel-consonant-vowel sequences where the consonant is a bilabial stop consonant /p, b/ and the vowels one of /i, a, u/; only asymmetrical vowel contexts were included in the analysis. Four subjects participated. Articulatory movements were recorded using a magnetometer system. The onset of the tongue movement from the first to the second vowel almost always occurred before the oral closure. Most of the tongue movement trajectory from the first to the second vowel took place during the oral closure for the stop. For all subjects, the onset of the tongue movement occurred earlier with respect to the onset of the lip closing movement as the tongue movement trajectory increased. The influence of consonant voicing and vowel context on interarticulator timing and tongue movement kinematics varied across subjects. Overall, the results are compatible with the hypothesis that there is a temporal window before the oral closure for the stop during which the tongue movement can start. A very early onset of the tongue movement relative to the stop closure together with an extensive movement before the closure would most likely produce an extra vowel sound before the closure.     

A three-dimensional model of tongue movement based on ultrasound and x-ray microbeam data

Point-tracking techniques provide timing information about structural movements of the tongue. Imaging techniques provide information about cross-sectional and pharyngeal tongue shape and movement. This study joined these techniques in a single subject. Five pellets on the tongue surface were tracked using x-ray microbeam, and the midsagittal and coronal planes of the tongue were imaged using real-time ultrasound. The speech materials were the consonants [s] and [l] and the vowels [i], [a], and [o] combined in VCVCe utterances. Analyses concentrated on the difference in tongue movements related to the two consonants. A model of tongue movement was developed, in which critical features of consonant shape and position dominated the tongue opening movement. In this model, the tongue is divided into subdivisions termed "functional segments" in both the sagittal and coronal planes. Movements of the functional segments created observable opening movement patterns.     

Control of phonemic length contrast and speech rate in vocalic and consonantal syllable nuclei

This paper investigates the mechanisms controlling the phonemic quantity contrast and speech rate in nonsense p(1)Np(2)a words read by five Slovak speakers in normal and fast speech rate. N represents a syllable nucleus, which in Slovak corresponds to long and short vowels and liquid consonants. The movements of the lips and the tongue were recorded with an electromagnetometry system. Together with the acoustic durations of p(1), N, and p(2), gestural characteristics of three core movements were extracted: p(1) lip opening, tongue movement for (N)ucleus, and p(2) lip closing. The results show that, although consonantal and vocalic nuclei are predictably different on many kinematic measures, their common phonological behavior as syllabic nuclei may be linked to a stable temporal coordination of the consonantal gestures flanking the nucleus. The functional contrast between phonemic duration and speech rate was reflected in the bias in the control mechanisms they employed: the strategies robustly used for signaling phonemic duration, such as the degree of coproduction of the two lip movements, showed a minimal effect of speech rate, while measures greatly affected by speech rate, such as p(2) acoustic duration, or the degree of p(1)-N gestural coproduction, tended to be minimally influenced by phonemic quantity.     

Control of rate and duration of speech movements

A computerized pulsed-ultrasound system was used to monitor tongue dorsum movements during the production of consonant-vowel sequences in which speech rate, vowel, and consonant were varied. The kinematics of tongue movement were analyzed by measuring the lowering gesture of the tongue to give estimates of movement amplitude, duration, and maximum velocity. All three subjects in the study showed reliable correlations between the amplitude of the tongue dorsum movement and its maximum velocity. Further, the ratio of the maximum velocity to the extent of the gesture, a kinematic indicator of articulator stiffness, was found to vary inversely with the duration of the movement. This relationship held both within individual conditions and across all conditions in the study such that a single function was able to accommodate a large proportion of the variance due to changes in movement duration. As similar findings have been obtained both for abduction and adduction gestures of the vocal folds and for rapid voluntary limb movements, the data suggest that a wide range of changes in the duration of individual movements might all have a similar origin. The control of movement rate and duration through the specification of biomechanical characteristics of speech articulators is discussed.     

Temporal measures of anticipatory labial coarticulation for the vowel/u/: within- and cross-subject variability.

The timing of upper lip protrusion movements and accompanying acoustic events was examined for multiple repetitions of word pairs such as "lee coot" and "leaked coot" by four speakers of American English. The duration of the intervocalic consonant string was manipulated by using various combinations of /s/, /t/, /k/, /h/, and /#/. Pairwise comparisons were made of consonant string duration (acoustic /i/ offset to acoustic /u/ onset) with durations of: protrusion movement beginning to acoustic /u/ onset, maximum acceleration of the movement to acoustic /u/ onset, and acoustic /u/ onset to movement end. There were some consonant-specific protrusion effects, primarily on the movement beginning event for /s/. Inferences from measures of the maximum acceleration and movement end events for the non-/s/ subset suggested the simultaneous and variable expression of three competing constraints: (1) end the protrusion movement during the voiced part of the /u/; (2) use a preferred movement duration; and (3) begin the /u/-related protrusion movement when permitted by relaxation of the perceptually motivated constraint that the preceding /i/ be unrounded. The subjects differed in the degree of expression of each constraint, but the results generally indicate that anticipatory coarticulation of lip protrusion is influenced both by acoustic-phonetic context dependencies and dynamical properties of movements. Because of the extensive variation in the data and the small number of subjects, these ideas are tentative; additional work is needed to explore them further.     

Economy of effort in different speaking conditions. II. Kinematic performance spaces for cyclical and speech movements

This study was designed to test the hypothesis that the kinematic manipulations used by speakers in different speaking conditions are influenced by kinematic performance limits. A range of kinematic parameter values was elicited by having seven subjects produce cyclical CV movements of lips, tongue blade and tongue dorsum (/ba/, /da/, /ga/), at rates ranging from 1 to 6 Hz. The resulting measures were used to establish speaker- and articulator-specific kinematic performance spaces, defined by movement duration, displacement and peak speed. These data were compared with speech movement data produced by the subjects in several different speaking conditions in the companion study (Perkell et al., 2002). The amount of overlap of the speech data and cyclical data varied across speakers, from almost no overlap to complete overlap. Generally, for a given movement duration, speech movements were larger than cyclical movements, indicating that the speech movements were faster and were produced with greater effort, according to the performance space analysis. It was hypothesized that the cyclical movements of the tongue and lips were slower than the speech movements because they were more constrained by (coupled to) the relatively massive mandible. To test this hypothesis, a comparison was made of cyclical movements in maxillary versus mandibular frames of reference. The results indicate that the cyclical movements were not strongly constrained by mandible movements. The overall results generally indicate that the cyclical task did not succeed in defining the upper limits of kinematic performance spaces within which the speech data were confined. Thus, the hypothesis that performance limits influence speech kinematics could not be tested effectively. The differences between the speech and cyclical movements may be due to other factors, such as differences in speakers' "skill" with the two types of movement, or the size of the movements--the speech movements were larger, probably because of a well-defined target for the primary, stressed vowel.     

Interacting effects of syllable and phrase position on consonant articulation

The complexities of how prosodic structure, both at the phrasal and syllable levels, shapes speech production have begun to be illuminated through studies of articulatory behavior. The present study contributes to an understanding of prosodic signatures on articulation by examining the joint effects of phrasal and syllable position on the production of consonants. Articulatory kinematic data were collected for five subjects using electromagnetic articulography (EMA) to record target consonants (labial, labiodental, and tongue tip), located in (1) either syllable final or initial position and (2) either at a phrase edge or phrase medially. Spatial and temporal characteristics of the consonantal constriction formation and release were determined based on kinematic landmarks in the articulator velocity profiles. The results indicate that syllable and phrasal position consistently affect the movement duration; however, effects on displacement were more variable. For most subjects, the boundary-adjacent portions of the movement (constriction release for a preboundary coda and constriction formation for a postboundary onset) are not differentially affected in terms of phrasal lengthening-both lengthen comparably.     

The cricothyroid muscle in voicing control

Initiation and maintenance of vibrations of the vocal folds require suitable conditions of adduction, longitudinal tension, and transglottal airflow. Thus manipulation of adduction/abduction, stiffening/slackening, or degree of transglottal flow may, in principle, be used to determine the voicing status of a speech segment. This study explores the control of voicing and voicelessness in speech with particular reference to the role of changes in the longitudinal tension of the vocal folds, as indicated by cricothyroid (CT) muscle activity. Electromyographic recordings were made from the CT muscle in two speakers of American English and one speaker of Dutch. The linguistic material consisted of reiterant speech made up of CV syllables where the consonants were voiced and voiceless stops, fricatives, and affricates. Comparison of CT activity associated with the voiced and voiceless consonants indicated a higher level for the voiceless consonants than for their voiced cognates. Measurements of the fundamental frequency (F0) at the beginning of a vowel following the consonant show the common pattern of higher F0 after voiceless consonants. For one subject, there was no difference in cricothyroid activity for voiced and voiceless affricates; in this case, the consonant-induced variations in the F0 of the following vowel were also less robust. Consideration of timing relationships between the EMG curves for voiced and voiceless consonants suggests that the differences most likely reflect control of vocal-fold tension for maintenance or suppression of phonatory vibrations. The same mechanism also seems to contribute to the well-known difference in F0 at the beginning of vowels following voiced and voiceless consonants.     

Positional targets for lingual consonants defined using electromagnetic articulography

The study examined the positional targets for lingual consonants defined using a point-parameterized approach with Wave (NDI, Waterloo, ON, Canada). The overall goal was to determine which consonants had unique tongue positions with respect to other consonants. Nineteen talkers repeated vowel-consonant-vowel (VCV) syllables that included consonants /t, d, s, z, , k, g/ in symmetrical vowel contexts /i, u, a/, embedded in a carrier phrase. Target regions for each consonant, characterized in terms of x,y,z tongue positions at the point of maximum tongue elevation, were extracted. Distances and overlaps were computed between all consonant pairs and compared to the distances and overlaps of their contextual targets. Cognates and postalveolar homorganics were found to share the location of their target regions. On average, alveolar stops showed distinctively different target regions than alveolar fricatives, which in turn showed different target region locations than the postalveolar consonants. Across talker variability in target locations was partially explained by differences in habitual speaking rate and hard palate characteristics.     

An examination of intra-articulator relative timing

The relative timing of consonant and vowel related movements of the tongue dorsum across variations in stress patterns was examined in two subjects using a computerized pulsed ultrasound system. The patterns observed were similar to those reported by Tuller et al. [J. Exp. Psychol. H.P.P. 8, 460-472 (1982)] for interarticulator timing. Correlations between the duration of a "period," defined as the interval between the onsets of movements associated with adjacent vowels, and the "latency," defined as the interval between the beginning of the period and the point in the period at which movement associated with the intervocalic consonant begins, were positive and reliable. The source of this correlation pattern was examined and found not to be due to a scaling of an invariant phase relation but rather due to a main effect for stress on the vowel-to-vowel articulatory period combined with an artifactual part-whole correlation within each stress level.     

Effects of prosodic boundary on /aC/ sequences: articulatory results

This study presents EMA (electromagnetic articulography) data on articulation of the vowel /a/ at different prosodic boundaries in French. Three speakers of metropolitan French produced utterances containing the vowel /a/, preceded by /t/ and followed by one of six consonants /b d g f s S/ (three stops and three fricatives), with different prosodic boundaries intervening between the /a/ and the six different consonants. The prosodic boundaries investigated are the Utterance, the Intonational phrase, the Accentual phrase, and the Word. Data for the Tongue Tip, Tongue Body, and Jaw are presented. The articulatory data presented here were recorded at the same time as the acoustic data presented in Tabain [J. Acoust. Soc. Am. 113, 516-531 (2003)]. Analyses show that there is a strong effect on peak displacement of the vowel according to the prosodic hierarchy, with the stronger prosodic boundaries inducing a much lower Tongue Body and Jaw position than the weaker prosodic boundaries. Durations of both the opening movement into and the closing movement out of the vowel are also affected. Peak velocity of the articulatory movements is also examined, and, contrary to results for phrase-final lengthening, it is found that peak velocity of the opening movement into the vowel tends to increase with the higher prosodic boundaries, together with the increased magnitude of the movement between the consonant and the vowel. Results for the closing movement out of the vowel and into the consonant are not so clear. Since one speaker shows evidence of utterance-level articulatory declension, it is suggested that the competing constraints of articulatory declension and prosodic effects might explain some previous results on phrase-final lengthening.     

Acoustic Analysis of Consonants in Whispered Speech

An acoustic analysis of whispered consonants in comparison to normally phonated consonants was conducted in time and intensity domains. Consonant duration and average root mean square intensity were measured for six speakers in both articulation modes. Each of 25 Serbian consonants (C) was sited between the vowel /a/ forming a syllable of /aCa/ type. Such a syllable was placed in initial, medial, and final position in the carrier sentence. Results showed that whispered consonants have a prolonged duration of about 10% on average (statistically significant, ANOVA test), and that the unvoiced consonants have a smaller time dimension extension (5.8%) than voiced ones (15.3%). Examination at subphonemic level showed that there is no difference in voice-onset-time and affrication duration in unvoiced plosives and affricates, in both whispered and phonated mode of articulation, but the difference is significant for voiced ones. Analysis of consonant duration versus place of articulation showed that palatal place is most sensitive in the process of whispering. In all experiments, the results are very consistent with respect to the subjects and test material (Pearson's correlation was between 0.6 and 0.9). In intensity domain, all unvoiced consonants in whispered mode of articulation have almost unchanged intensity in comparison to phonated mode (the difference is maximum 3.5 dB). On the contrary, voiced consonants in the whispered mode were reduced in intensity by as much as 25 dB, as nasals and semivowels. Average intensity of whispered consonants is lowered by 12d B in comparison to phonated ones, and does not depend on syllabic position inside the sentences.     

A timing model for word-initial CV syllables in Modern Greek

Measurements of the temporal characteristics of word-initial stressed syllables in CV CV-type words in Modern Greek showed that the timing of the initial consonant in terms of its closure duration and voice onset time (VOT) is dependent on place and manner of articulation. This is contrary to recent accounts of word-initial voiceless consonants in English which propose that closure and VOT together comprise a voiceless interval independent of place and manner of articulation. The results also contribute to the development of a timing model for Modern Greek which generates closure, VOT, and vowel durations for word-initial, stressed CV syllables. The model is made up of a series of rules operating in an ordered fashion on a given word duration to derive first a stressed syllable duration and then all intrasyllabic acoustic intervals.     

Spectral and duration properties of front vowels as cues to final stop-consonant voicing

The perception of voicing in final velar stop consonants was investigated by systematically varying vowel duration, change in offset frequency of the final first formant (F1) transition, and rate of frequency change in the final F1 transition for several vowel contexts. Consonant-vowel-consonant (CVC) continua were synthesized for each of three vowels, [i,I,ae], which represent a range of relatively low to relatively high-F1 steady-state values. Subjects responded to the stimuli under both an open- and closed-response condition. Results of the study show that both vowel duration and F1 offset properties influence perception of final consonant voicing, with the salience of the F1 offset property higher for vowels with high-F1 steady-state frequencies than low-F1 steady-state frequencies, and the opposite occurring for the vowel duration property. When F1 onset and offset frequencies were controlled, rate of the F1 transition change had inconsistent and minimal effects on perception of final consonant voicing. Thus the findings suggest that it is the termination value of the F1 offset transition rather than rate and/or duration of frequency change, which cues voicing in final velar stop consonants during the transition period preceding closure.     

Locus equations are an acoustic expression of articulator synergy

The study investigated the articulatory basis of locus equations, regression lines relating F2 at the start of a Consonant-Vowel (CV) transition to F2 at the middle of the vowel, with C fixed and V varying. Several studies have shown that consonants of different places of articulation have locus equation slopes that descend from labial to velar to alveolar, and intercept magnitudes that increase in the opposite order. Using formulas from the theory of bivariate regression that express regression slopes and intercepts in terms of standard deviations and averages of the variables, it is shown that the slope directly encodes a well-established measure of coarticulation resistance. It is also shown that intercepts are directly related to the degree to which the tongue body assists the formation of the constriction for the consonant. Moreover, it is shown that the linearity of locus equations and the linear relation between locus equation slopes and intercepts originates in linearity in articulation between the horizontal position of the tongue dorsum in the consonant and to that in the vowel. It is concluded that slopes and intercepts of acoustic locus equations are measures of articulator synergy.