Variation in anticipatory coarticulation with changes in clarity and rate.

This study tests the hypothesis that the relative timing, or coarticulation, of articulatory movements at VC and CV boundaries is influenced by both the listener's requirement for clarity and the speaker's strategy to economize effort. Movement and acoustic data were collected from 7 subjects who spoke in three conditions: normal, clear, and fast. It was predicted that fast speech would show more coarticulation and clear speech would show less coarticulation than normal speech. The speech materials were designed to investigate coarticulation in the movements of the upper lip and tongue. They consisted of repetitions of [iC(n)u] utterances embedded in carrier phrases, where the number of consonants, n, ranged from 1 to 3. Analyses focused on kinematic measures and the amount of coarticulation (overlap) of the /i-u/ transition movement with the acoustic interval of the /i/. The consonant-string duration was longest in the clear speaking condition and shortest in the fast condition. Compared to the normal condition, peak velocities were higher in the fast and clear speaking conditions, indicating increased effort. The influences of speaking condition on coarticulation and on the formants of the /i/ were small. Thus, even though there was evidence of increased effort in the clear and fast conditions, the hypothesized effects of a trade-off between clarity and economy of effort were minimally evident in formant values for /i/ and measures of coarticulation.

Covariation of cochlear implant users' perception and production of vowel contrasts and their identification by listeners with normal hearing.

This study investigates covariation of perception and production of vowel contrasts in speakers who use cochlear implants and identification of those contrasts by listeners with normal hearing. Formant measures were made of seven vowel pairs whose members are neighboring in acoustic space. The vowels were produced in carrier phrases by 8 postlingually deafened adults, before and after they received their cochlear implants (CI). Improvements in a speaker's production and perception of a given vowel contrast and normally hearing listeners' identification of that contrast in masking noise tended to occur together. Specifically, speakers who produced vowel pairs with reduced contrast in the pre-CI condition (measured by separation in the acoustic vowel space) and who showed improvement in their perception of these contrasts post-CI (measured with a phoneme identification test) were found to have enhanced production contrasts post-CI in many cases. These enhanced production contrasts were associated, in turn, with enhanced masked word recognition, as measured from responses of a group of 10 normally hearing listeners. The results support the view that restoring self-hearing allows a speaker to adjust articulatory routines to ensure sufficient perceptual contrast for listeners.

Changes in speech intelligibility of postlingually deaf adults after cochlear implantation.

OBJECTIVE: This study examines changes in the intelligibility of CVC words spoken by postlingually deafened adults after they have had 6 to 12 mo of experience with a cochlear implant. The hypothesis guiding the research is that the intelligibility of these speakers will improve after extended use of a cochlear implant. The paper also describes changes in CVC word intelligibility analyzed by phoneme class and by features. DESIGN: The speech of eight postlingually deaf adults was recorded before activation of the speech processors of their cochlear implants and at 6 mo and 1 yr after activation. Seventeen listeners with no known impairment of hearing completed a word identification task while listening to each implant user's speech in noise. The percent information transmitted by the speakers in their pre- and postactivation recordings was measured for 11 English consonants and eight vowels separately. RESULTS: An overall improvement in word intelligibility was observed: seven of the eight speakers showed improvement in vowel intelligibility and six speakers showed improvement in consonant intelligibility. However, the intelligibility of specific consonant and vowel features varied greatly across speakers. CONCLUSIONS: Extended use of a cochlear implant by postlingually deafened adults tends to enhance their intelligibility.

Articulatory tradeoffs reduce acoustic variability during American English /r/ production.

The American English phoneme /r/ has long been associated with large amounts of articulatory variability during production. This paper investigates the hypothesis that the articulatory variations used by a speaker to produce /r/ in different contexts exhibit systematic tradeoffs, or articulatory trading relations, that act to maintain a relatively stable acoustic signal despite the large variations in vocal tract shape. Acoustic and articulatory recordings were collected from seven speakers producing /r/ in five phonetic contexts. For every speaker, the different articulator configurations used to produce /r/ in the different phonetic contexts showed systematic tradeoffs, as evidenced by significant correlations between the positions of transducers mounted on the tongue. Analysis of acoustic and articulatory variabilities revealed that these tradeoffs act to reduce acoustic variability, thus allowing relatively large contextual variations in vocal tract shape for /r/ without seriously degrading the primary acoustic cue. Furthermore, some subjects appeared to use completely different articulatory gestures to produce /r/ in different phonetic contexts. When viewed in light of current models of speech movement control, these results appear to favor models that utilize an acoustic or auditory target for each phoneme over models that utilize a vocal tract shape target for each phoneme.

Tongue surface displacement during bilabial stops.

The goals of this study were to characterize tongue surface displacement during production of bilabial stops and to refine current estimates of vocal-tract wall impedance using direct measurements of displacement in the vocal tract during closure. In addition, evidence was obtained to test the competing claims of passive and active enlargement of the vocal tract during voicing. Tongue displacement was measured and tongue compliance was estimated in four subjects during production of /aba/ and /apa/. All subjects showed more tongue displacement during /aba/ than during /apa/, even though peak intraoral pressure is lower for /aba/. In consequence, compliance estimates were much higher for /aba/, ranging from 5.1 to 8.5 x 10(-5) cm3/dyn. Compliance values for /apa/ ranged from 0.8 to 2.3 x 10(-5) cm3/dyn for the tongue body, and 0.52 x 10(-5) for the single tongue tip point that was measured. From combined analyses of tongue displacement and intraoral pressure waveforms for one subject, it was concluded that smaller tongue displacements for /p/ than for /b/ may be due to active stiffening of the tongue during /p/, or to intentional relaxation of tongue muscles during /b/ (in conjunction with active tongue displacement during /b/).

Comparisons among aerodynamic, electroglottographic, and acoustic spectral measures of female voice.

This study examines measures of the glottal airflow waveform, the electroglottographic signal (EGG), amplitude differences between peaks in the acoustic spectrum, and observations of the spectral energy content of the third formant (F3), in terms of how they relate to one another. Twenty females with normal voices served as subjects. Both group and individual data were studied. Measurements were made for the vowel in two speech tasks: strings of the syllable /pae/and sustained phonation of /ae/, which were produced at two levels of vocal effort: comfortable and loud voice. The main results were: 1. Significant differences in parameter values between /pae/and/ae/were related to significant differences in the sound pressure level (SPL). 2. An "adduction quotient," measured from the glottal waveform at a 30% criterion, was sensitive enough to differentiate between waveforms reflecting abrupt versus gradual vocal fold closing movements. 3. DC flow showed weak or nonsignificant relationships with acoustic measures. 4. The spectral content in the third formant (F3) in comfortable loudness typically consisted of a mix of noise and harmonic energy. In loud voice, the F3 spectral content typically consisted of harmonic energy. 5. Significant differences were found in all measures between tokens with F3 harmonic energy and tokens with F3 noise, independent of loudness condition. 6. Strong relationships between flow- and EGG-adduction quotients suggested that these signals can be used to complement each other. 7. The amplitude difference between spectral peaks of the first and third formant (F1-F3) was found to add information about abruptness of airflow decrease (flow declination) that may be lost in the glottal waveform signal due to low-pass filtering. The results are discussed in terms of how an integrated use of these measures can contribute to a better understanding of the normal vocal mechanism and help to improve methods for evaluating vocal function.

A preliminary study of the effects of cochlear implants on the production of sibilants.

The potential influence of auditory information in the production of /s/ and /integral of/ was explored for postlingually deafened adults with four-channel Ineraid cochlear implants. Analyses of the spectra of the sibilant sounds were compared for speech obtained prior to implant activation, after early implant use and after 6 months of use. In addition, the output of the Ineraid device (measured at each of the four electrodes) was analyzed with pre- and postactivation speech samples to explore whether the speech production changes were potentially audible to the cochlear-implant user. Results indicated that subjects who showed abnormally low or incorrect contrast between /s/ and /integral of/ preactivation, and who received significant auditory benefit from their implants were able to increase the distinctiveness of their productions of the two speech sounds.

Group differences in measures of voice production and revised values of maximum airflow declination rate.

In previous reports, aerodynamic and acoustic measures of voice production were presented for groups of normal male and female speakers [Holmberg et al., J. Acoust. Soc. Am. 84, 511-529 (1988); J. Voice 3, 294-305 (1989)] that were used as norms in studies of voice disorders [Hillman et al., J. Speech Hear. Res. 32, 373-392 (1989); J. Voice 4, 52-63 (1990)]. Several of the measures were extracted from glottal airflow waveforms that were derived by inverse filtering a high-time-resolution oral airflow signal. Recently, the methods have been updated and a new study of additional subjects has been conducted. This report presents previous (1988) and current (1993) group mean values of sound pressure level, fundamental frequency, maximum airflow declination rate, ac flow, peak flow, minimum flow, ac-dc ratio, inferred subglottal air pressure, average flow, and glottal resistance. Statistical tests indicate overall group differences and differences for values of several individual parameters between the 1988 and 1993 studies. Some inter-study differences in parameter values may be due to sampling effects and minor methodological differences; however, a comparative test of 1988 and 1993 inverse filtering algorithms shows that some lower 1988 values of maximum flow declination rate were due at least in part to excessive low-pass filtering in the 1988 algorithm. The observed differences should have had a negligible influence on the conclusions of our studies of voice disorders.

Relationships between intra-speaker variation in aerodynamic measures of voice production and variation in SPL across repeated recordings.

Intra-speaker variation in aerodynamic and acoustic measures of voice production across repeated recordings was studied in relation to cross-recording variation in SPL for three normal female and three normal male speakers. Group data for 15 females and 15 males served as the statistical reference. The speech material consisted of syllable strings in soft, normal, and loud voice. Measures were made of (a) parameters characterizing the inverse filtered oral airflow waveform, (b) the inferred average transglottal air pressure and glottal airflow, and (c) SPL. The results showed that intra-speaker parameter variation across recordings was generally less than 2 standard deviations relative to group mean values. In terms of relation to variation in SPL, the measures could be divided into two main groups: (a) For air pressure, AC flow, and maximum flow declination rate, both intra-speaker variation across recordings and inter-speaker (group) variation was related systematically to variation of SPL. For these measures, it is suggested that variation across recordings was due in part to SPL differences, which can be adjusted for statistically, thus facilitating comparisons between absolute values. (b) For other measures, neither intra-speaker variation across recordings nor inter-speaker group variation was systematically related to SPL. However, some of these latter measures changed with SPL in an orderly fashion across soft, normal, and loud voice for individual speakers. The results are discussed in terms of the clinical use of these measures in studies of voice disorders.

Individual variation in measures of voice.

Measures of inferred subglottal air pressure, glottal airflow waveform characteristics, sound pressure level (SPL) and the acoustic spectral slope were studied for individual speakers with normal voices. Combinations of different levels of subglottal air pressure and varying glottal configurations could result in the same SPL. Relatively high air pressure levels were associated with a steep spectral slope, reflecting a more sinusoidal glottal waveform and a relatively abducted membranous glottis, which would result in damping of F1. Data suggested that the interarytenoid glottal opening could vary without systematically affecting SPL or voice quality. The results indicate that the principles of production-related economy of effort and physiological, acoustic and perceptual constraints may apply to voice production.

Trading relations between tongue-body raising and lip rounding in production of the vowel /u/: a pilot "motor equivalence" study.

Articulatory and acoustic data were used to explore the following hypothesis for the vowel /u/: The objective of articulatory movements is an acoustic goal; varying and reciprocal contributions of different articulators may help to constrain acoustic variation in achieving the goal. Previous articulatory studies of similar hypotheses, expressed entirely in articulatory terms, have been confounded by interdependencies of the variables being studied (e.g., lip and mandible displacements). One case in which this problem may be minimized is that of lip rounding and tongue-body raising (formation of a velo-palatal constriction) for the vowel /u/. Lip rounding and tongue-body raising should have similar acoustic effects for /u/, mainly to lower F2. In multiple repetitions, reciprocal contributions of lip rounding and tongue-body raising could help limit F2 variability for /u/; thus this experiment looked for complementary covariation (negative correlations) in measures of these two parameters. An electro-magnetic midsagittal articulometer (EMMA) was used to track movements of midsagittal points on the tongue body, upper and lower lips, and mandible for large numbers of repetitions of utterances containing /u/. (Interpretation of the data was aided by results from area-function-to-formant modeling.) Three of four subjects showed weak negative correlations, tentatively supporting the hypothesis; a fourth showed the opposite pattern: positive correlations of lip rounding and tongue raising. The results are discussed with respect to ideas about motor equivalence, the nature of speech motor programming, and potential improvements to the paradigm.

Electromagnetic midsagittal articulometer systems for transducing speech articulatory movements.

This paper describes two electromagnetic midsagittal articulometer (EMMA) systems that were developed for transducing articulatory movements during speech production. Alternating magnetic fields are generated by transmitter coils that are mounted in an assembly that fits on the head of a speaker. The fields induce alternating voltages in a number of small transducer coils that are attached to articulators in the midline plane, inside and outside the vocal tract. The transducers are connected by fine lead wires to receiver electronics whose output voltages are processed to yield measures of transducer locations as a function of time. Measurement error can arise with this method, because as the articulators move and change shape, the transducers can undergo a varying amount of rotational misalignment with respect to the transmitter axes; both systems are designed to correct for transducer misalignment. For this purpose, one system uses two transmitters and biaxial transducers; the other uses three transmitters and single-axis transducers. The systems have been compared with one another in terms of their performance, human subjects compatibility, and ease of use. Both systems can produce useful midsagittal-plane data on articular movement, and each one has a specific set of advantages and limitations. (Two commercially available systems are also described briefly for comparison purposes). If appropriate experimental controls are used, the three-transmitter system is preferable for practical reasons.

Effects of short-term auditory deprivation on speech production in adult cochlear implant users.

Speech production parameters of three postlingually deafened adults who use cochlear implants were measured: after 24 h of auditory deprivation (which was achieved by turning the subject's speech processor off); after turning the speech processor back on; and after turning the speech processor off again. The measured parameters included vowel acoustics [F1, F2, F0, sound-pressure level (SPL), duration and H1-H2, the amplitude difference between the first two spectral harmonics, a correlate of breathiness] while reading word lists, and average airflow during the reading of passages. Changes in speech processor state (on-to-off or vice versa) were accompanied by numerous changes in speech production parameters. Many changes were in the direction of normalcy, and most were consistent with long-term speech production changes in the same subjects following activation of the processors of their cochlear implants [Perkell et al., J. Acoust. Soc. Am. 91, 2961-2978 (1992)]. Changes in mean airflow were always accompanied by H1-H2 (breathiness) changes in the same direction, probably due to underlying changes in laryngeal posture. Some parameters (different combinations of SPL, F0, H1-H2 and formants for different subjects) showed very rapid changes when turning the speech processor on or off. Parameter changes were faster and more pronounced, however, when the speech processor was turned on than when it was turned off. The picture that emerges from the present study is consistent with a dual role for auditory feedback in speech production: long-term calibration of articulatory parameters as well as feedback mechanisms with relatively short time constants.

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.

A system for signal processing and data extraction from aerodynamic, acoustic, and electroglottographic signals in the study of voice production.

A software system, implemented in the MITSYN languages, is described for signal processing and data extraction from oral airflow, intra-oral air pressure, vocal fold contact area (EGG) and sound pressure signals. Signal processing algorithms are specified in the form of block diagrams; examples are shown for demultiplexing signals into bandwidth-specific, time-aligned signal stream files and for inverse filtering the oral airflow waveform to obtain an approximation of the glottal airflow waveform. Interactive and algorithmic data extraction is performed with a menu-driven procedure that displays the stages of analysis, graphical indications of the results of algorithmically made decisions, and derived results. The system has proven to be useful for obtaining quantities of detailed data on voice production.

Objective assessment of vocal hyperfunction: an experimental framework and initial results.

This report describes the experimental design and initial results of an ongoing clinical investigation of voice disorders. Its major focus is the development and use of quantitative measures to provide objective descriptions of conditions referred to as "vocal hyperfunction." The experimental design for this project is based on a descriptive theoretical framework, which holds that there are different types and stages of hyperfunctionally related voice disorders. Data consist of indirect measures derived from noninvasive aerodynamic and acoustic recordings including (a) parameters derived from inverse filtered approximations of the glottal air flow waveform; (b) estimates of transglottal pressure, average glottal air flow, glottal resistance and vocal efficiency; and (c) measures of vocal intensity and fundamental frequency. Initial results (based on comparisons among 15 voice patients and 45 normal speakers) support major assumptions that underlie the theoretical framework, and indicate that the measurement approach being utilized is capable of differentiating hyperfunctional from normal voices and hyperfunctional conditions from one another. Organic manifestations of vocal hyperfunction (nodules, polyps, contact ulcers) are accompanied by abnormally high values for the glottal waveform parameters of AC flow and maximum flow declination rate, suggesting increased potential for vocal fold trauma due to high vocal fold closure velocities and collision forces. In contrast, nonorganic manifestations of hyperfunction (functional disorders) tend to be associated with abnormally high levels of unmodulated DC flow, without high values for AC flow and maximum flow declination rate, suggesting reduced potential for vocal fold trauma. Measures also suggest different underlying mechanisms for nodules and polyps as compared to contact ulcers. Results are discussed relative to predictions based on the theoretical framework for vocal hyperfunction.

Glottal airflow and transglottal air pressure measurements for male and female speakers in soft, normal, and loud voice.

Measurements on the inverse filtered airflow waveform (the "glottal waveform") and of estimated average transglottal pressure and glottal airflow were made from noninvasive recordings of productions of syllable sequences in soft, normal, and loud voice for 25 male and 20 female speakers. Statistical analyses showed that with change from normal to loud voice, both males and females produced loud voice with increased pressure, accompanied by increased ac flow and increased maximum airflow declination rate. With change from normal voice, soft voice was produced with decreased pressure, ac flow and maximum airflow declination rate, and increased dc and average flow. Within the loudness conditions, there was no significant male-female difference in air pressure. Several glottal waveform parameters separated males and females in normal and loud voice. The data indicate higher ac flow and higher maximum airflow declination rate for males. In soft voice, the male and female glottal waveforms were more alike, and there was no significant difference in maximum airflow declination rate. The dc flow did not differ significantly between males and females. Possible relevance to biomechanical differences and differences in voice source characteristics between males and females and across loudness conditions is discussed.

Variability in production of the vowels /i/ and /a/.

A hypothesis on the nature of articulatory targets for the vowels /i/ and /a/ is proposed, based on acoustic considerations and vowel articulations. The conjecture is that positioning of points on the tongue surface in a repetition experiment should be most accurate in the direction perpendicular to the vocal-tract midline, at the acoustically critical point of maximal constriction for each vowel. The hypothesis was tested by: examining x-ray microbeam data for three speakers, conducting a partial acoustical analysis, and performing a modeling study. Distributions were plotted of the midsagittal locations of three tongue points at the time of maximal excursion toward the vowel target for numbers of examples of the vowels, embedded in a variety of phonetic contexts. More variation was found along a direction parallel to the vocal tract midline than perpendicular to the midline, supporting the hypothesis. Statistics on formant values for one subject have been calculated, and pairwise regressions of displacement and formant data have been run. An articulatory synthesizer [Rubin et al., J. Acoust. Soc. Am. 70, 321-328 (1981)] has been manipulated through displacements similar to the subject's articulatory variation. Although articulatory synthesis showed systematic relationships between articulatory relationships and formant frequencies, there were no significant correlations between the subject's measured articulatory displacements and his formant data. These additional results raise questions about the methodology and point to the need for additional work for an adequate test of the hypothesis.

Mandible movements during increasingly rapid articulations of single syllables: preliminary observations.

A previous study of mandible movements in normal speech [W.L. Nelson, J. Acoust. Soc. Am. Suppl. 1 68, S32 (1980)] suggested that the speech motor control process resulted in a relationship between movement time, distance, and peak velocity which implied (1) some adaptation to the physical effort required for the movement, and (2) that the force limit effective during speech was considerably below that which the mandibular muscles are capable of producing. In the present study, mandible movements were measured during maximally rapid opening and closing tasks, and during increasingly rapid repetitions of a spoken syllable and a nonspeech "syllable." The results indicate that (1) peak acceleration levels for the repeated mandible movements were less than half of those for the maximally rapid single mandible movements, and (2) a rather different mode of control is used for the repeated speech movements as compared to the nonspeech movements.