Effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts.

PURPOSE: To assess the effects of short- and long-term changes in auditory feedback on vowel and sibilant contrasts and to evaluate hypotheses arising from a model of speech motor planning. METHOD: The perception and production of vowel and sibilant contrasts were measured in 8 postlingually deafened adults prior to activation of their cochlear implant speech processors, 1 month postactivation, and 1 year postactivation. Measures were taken postactivation both with and without auditory feedback. Contrast measures were also made for a group of speakers with reportedly normal hearing speaking with masked and unmasked auditory feedback. RESULTS: Vowel and sibilant contrasts, measured in the absence of auditory feedback after 1 month of prosthesis use, were diminished compared with their values measured before prosthesis. Contrasts measured in the absence of auditory feedback after 1 year's experience with the prosthesis were increased compared with their values after 1 month's experience. In both time samples, contrasts were enhanced when auditory feedback was restored. CONCLUSION: The provision of prosthetic hearing to postlingually deafened adults impaired their phonemic contrasts at first, as their auditory feedback had novel characteristics. Once auditory feedback became recalibrated with prosthesis use, it could, in turn, revise feedforward commands that control the contrasts in its absence.     

Vowel space characteristics and vowel identification accuracy.

PURPOSE: To examine the relation between vowel production characteristics and intelligibility. METHOD: Acoustic characteristics of 10 vowels produced by 45 men and 48 women from the J. M. Hillenbrand, L. A. Getty, M. J. Clark, and K. Wheeler (1995) study were examined and compared with identification accuracy. Global (mean f0, F1, and F2; duration; and amount of formant movement) and fine-grained measures (vowel space area; mean distance among vowels; f0, F1, and F2 ranges; duration ratio between long and short vowels; and formant movement ratio between dynamic and static vowels) were used to predict identification scores. Acoustic measures of the most frequently confused pairs (/ae/-/epsilon/ and /a/-/inverted v/) were compared. RESULTS: Global and fine-grained measures accounted for less than 1/4 of variance in identification scores: Vowel space area alone accounted for 9%-12% of variance. Differences in vowel identification were largely due to poor identification of /ae/, /epsilon/, /a/, or /inverted v/. Well-identified vowels were distinctive in formant frequencies, duration, and amount of formant movement over time. CONCLUSIONS: Distinctiveness among neighboring vowels is more important in determining vowel intelligibility than vowel space area. Acoustic comparison of confused vowels may be more useful in studying intelligibility of normal and disordered speech than in measuring vowel space area.     

Effect of spectral smearing on the perceptual segregation of vowel sequences

Although segregation of both simultaneous and sequential speech items may be involved in the reception of speech in noisy environments, research on the latter is relatively sparse. Further, previous studies examining the ability of hearing-impaired listeners to form distinct auditory streams have produced mixed results. Finally, there is little work investigating streaming in cochlear implant recipients, who also have poor frequency resolution. The present study focused on the mechanisms involved in the segregation of vowel sequences and potential limitations to segregation associated with poor frequency resolution. An objective temporal-order paradigm was employed in which listeners reported the order of constituent vowels within a sequence. In Experiment 1, it was found that fundamental frequency based mechanisms contribute to segregation. In Experiment 2, reduced frequency tuning often associated with hearing impairment was simulated in normal-hearing listeners. In that experiment, it was found that spectral smearing of the vowels increased accurate identification of their order, presumably by reducing the tendency to form separate auditory streams. These experiments suggest that a reduction in spectral resolution may result in a reduced ability to form separate auditory streams, which may contribute to the difficulties of hearing-impaired listeners, and probably cochlear implant recipients as well, in multi-talker cocktail-party situations.     

Effects of consonantal context on vowel lipreading

The effects of consonantal context on vowel lipreading were assessed for 30 adults with mild-to-moderate sensorineural hearing loss who lipread videotape recordings of two female talkers. The stimuli were the vowels /i,I,alpha,U,u/ in symmetric CVC form with the consonants /p,b,f,v,t,d,f,g/ and in the asymmetric consonantal contexts /h/-V-/g/, /w/-V-/g/, /r/-V-/g/. Analyses of the confusion matrices from each talker indicated that vowel intelligibility was significantly poorer in most contexts involving highly visible consonants, although the utterances of one talker were highly intelligible in the bilabial context. Among the visible contexts, the fricative and labiodental contexts in particular produced the lowest vowel intelligibility regardless of talker. Lax vowels were consistently more difficult to perceive than tense vowels. Implications for talker selection and refinement of the concept of viseme were drawn.     

Vocal register effects on vowel spectral noise and roughness: findings for adult females.

The effects of vocal register (vocal fry, modal, and falsetto) on the relative roughness and spectral noise level (SNL) of isolated test vowels (/u/ and/ae/) were investigated. Each of the three vocal registers; the obtained samples were magnetically recorded. A panel of 11 listeners independently verified by perceptual judgments that each recorded sample was produced in the "desired" vocal register. Also, they independently rated (on a 5-point equal-appearing intervals scale) the roughness of each test production. A median of the 11 roughness ratings (MRR) available was then obtained as an index of the roughness of each vowel sample. Additionally, a narrow-band (3 Hz) acoustic spectrum of each test production was made in which measures of vowel spectral noise were obtained. A mean over 25 noise measures per test production (from 100 to 2600 Hz) served as an index of the spectral noise level (SNL) for each vowel sample. The major finding in the study was that the MRR and the SNL for productions of both test vowels diminished significantly across vocal registers, from fry, to modal, to falsetto.     

Effects of talker variability on vowel recognition in cochlear implants.

PURPOSE: To investigate the effects of talker variability on vowel recognition by cochlear implant (CI) users and by normal-hearing (NH) participants listening to 4-channel acoustic CI simulations. METHOD: CI users were tested with their clinically assigned speech processors. For NH participants, 3 CI processors were simulated, using different combinations of carrier type and temporal envelope cutoff frequency (noise band/160 Hz, sine wave/160 Hz, and sine wave/20 Hz). Vowel recognition was measured for 4 talkers, presented in either a single-talker context (1 talker per test block) or a multi-talker context (4 talkers per test block). RESULTS: CI users' vowel recognition was significantly poorer in the multi-talker context than in the single-talker context. When noise-band carriers were used in the simulations, NH performance was not significantly affected by talker variability. However, when sine-wave carriers were used in the simulations, NH performance was significantly affected by talker variability in both envelope filter conditions. CONCLUSIONS: Because fundamental frequency was not preserved by the 20-Hz envelope filter and only partially preserved by the 160-Hz envelope filter, both spectral and temporal cues contributed to the talker variability effects observed with sine-wave carriers. Similarly, spectral and temporal cues may have contributed to the talker variability effects observed with CI participants.     

Age and laryngeal airway resistance during vowel production in women.

An investigation was conducted to determine if laryngeal valving economy, as reflected in measures of laryngeal airway resistance during vowel production, differs with age in women. Seventy healthy women were studied, 10 each at age 25, 35, 45, 55, 65, 75, and 85 years. Results indicated that laryngeal airway resistance did not differ significantly with age, although it was noted that the 45-year-old women generally had lower laryngeal airway resistance values. This pattern of function differs from that observed in men (Melcon, Hoit, & Hixon, 1989). Discussion of findings includes consideration of factors that might influence laryngeal function during speech production in women. Clinical implications are offered.     

Predicting midsagittal pharynx shape from tongue position during vowel production.

The shape of the pharynx has a large effect on the acoustics of vowels, but direct measurement of this part of the vocal tract is difficult. The present study examines the efficacy of inferring midsagittal pharynx shape from the position of the tongue, which is much more amenable to measurement. Midsagittal magnetic resonance (MR) images were obtained for multiple repetitions of 11 static English vowels spoken by two subjects (one male and one female). From these, midsagittal widths were measured at approximately 3-mm intervals along the entire vocal tract. A regression analysis was then used to assess whether the pharyngeal widths could be predicted from the locations and width measurements for four positions on the tongue, namely, those likely to be the locations of a receiver coil for an electromagnetometer system. Predictability was quite high throughout the vocal tract (multiple r> 0.9), except for the extreme ends (i.e., larynx and lips) and small decreases for the male subject in the uvula region. The residuals from this analysis showed that the accuracy of predictions was generally quite high, with 89.2% of errors being less than 2 mm. The extremes of the vocal tract, where the resolution of the MRI was poorer, accounted for much of the error. For languages like English, which do not use advanced tongue root (ATR) distinctively, the midsagittal pharynx shape of static vowels can be predicted with high accuracy.     

Relationship of spectral noise levels to psychophysical scaling of vowel roughness

Direct magnitude estimation (DME) and equal-appearing interval (EAI) ratings of perceived roughness and spectral noise level (SNL) measurements of isolated sustained vowel samples (/a/ and /i/) were obtained. The linear and curvilinear relationships between the resulting roughness ratings and SNL were then examined. In the present study, the comparison between the two models resulted in conflicting evidence regarding the model that best described the relationship between roughness ratings and SNL measurements. In all comparisons, however, a significant linear component was indicated. Additionally, when a significant curvilinear component was indicated, the difference between the lines and curves that were fit to the data was minimal. The present findings suggest, therefore, that a high degree of linearity exists between both DME and EAI roughness ratings and SNL.     

Bite block vowel production in apraxia of speech

PURPOSE: This study explored vowel production and adaptation to articulatory constraints in adults with acquired apraxia of speech (AOS) plus aphasia. METHOD: Five adults with acquired AOS plus aphasia and 5 healthy control participants produced the vowels [i], [epsilon], and [ae] in four word-length conditions in unconstrained and bite block conditions. In addition to acoustic and perceptual measures of vowel productions, individually determined idealized vowels based on each participant's best performance were used to assess vowel accuracy and distinctiveness. RESULTS: Findings showed (a) clear separation of vowel formants in speakers with AOS; (b) impaired vowel production in speakers with AOS, shown by perceptual measures of vowel quality and acoustic measures of vowel accuracy and contrastivity; and (c) incomplete compensation to bite block compensation both for individuals with AOS and for healthy controls. CONCLUSIONS: Although adults with AOS were less accurate overall in vowel production than unimpaired speakers, introduction of a bite block resulted in similar patterns of decreased vowel accuracy for the two groups. Findings suggest that feedback control for vowel production is relatively intact in these individuals with AOS and aphasia. Predominant use of feedback control mechanisms is hypothesized to account for characteristic vowel deficits of the disorder.     

Training effects on vowel production by two profoundly hearing-impaired speakers

Two profoundly hearing-impaired adolescents received systematic speech training to improve their production of the vowels /i/ and /ae/. Acoustic measures of F1, F2, and duration, and listener judgements of vowel acceptability, were used to quantify vowel production before and after training. Both subjects demonstrated significant changes in their production of the two vowels at the acoustic and perceptual levels following treatment. The changes were highly individualized. For some features, significant improvement occurred posttreatment with differences between the hearing-impaired subject and a control group of subjects with normal hearing no longer present. There was a significant improvement in the acceptability of the two vowels in each subject's speech after training. Vowel duration remained unchanged in the speech of one subject whereas it increased in the speech of the other subject following training. There was a trend toward reduced token-to-token variation in the posttreatment samples. Acoustic and perceptual measures also were obtained on two vowels not directly trained in the program. Significant changes occurred in the production of these segments but some of the changes resulted in greater deviation in the post- than in the pretreatment samples.     

Comparing tongue positioning by normal-hearing and hearing-impaired children during vowel production.

Glossometric measures of tongue positions of 10 normal-hearing (NH) and 10 profoundly hearing-impaired (HI) children were compared during production of the eight vowels /i,I,E,ae,u,U,o,a/. The NH subjects used tongue positions with distinct vertical distances from the hard palate and discrete tongue shapes to distinguish the front vowels and the back vowels. The HI subjects produced vowels using a reduced vertical range and singular flat, high-back tongue shape. Token-to-token variability was greater for the HI subjects. Listener identifications of the vowels produced by the HI subjects fell in three categories: highly variable responses to /i/, low vowels for /I,E,ae,a/, and back vowels for /u,U,o/. The centralized, generally undifferentiated tongue positions and listener identifications for the HI subjects coincided with suppositions made from previous perceptual, acoustic, and physiologic findings.     

The role of spectral and temporal cues in vowel identification by listeners with impaired hearing.

This study examined the use of duration and formant frequency in the labeling of synthetic CVC stimuli forming a beet-bit continuum. Durational and F2 frequency cues to vowel identity varied systematically across stimuli. Subjects with normal hearing tended to rely primarily on F2 frequency in vowel labeling, whereas subjects with impaired hearing relied less on F2 information. This group difference was observed even for stimuli with large F2 differences, which were easily discriminated by all subjects. The effect of vowel duration on labeling was similar for both groups, with long-duration stimuli receiving more "beet" responses than short-duration stimuli across the F2 range. Psychoacoustic measures of frequency resolution and temporal resolution were poor predictors of a subject's use of formant information and duration information in labeling.     

Pitch effects on vowel roughness and spectral noise for subjects in four musical voice classifications

This study was designed to investigate the effects of vocal fo on vowel spectral noise level (SNL) and perceived vowel roughness for subjects in high- and low-pitch voice categories. The subjects were 40 adult singers (10 each sopranos, altos, tenors, and basses). Each produced the vowel /a/ in isolation at a comfortable speaking pitch, and at each of seven assigned pitches spaced at whole-tone intervals over a musical octave within his or her singing pitch range. The eight /a/ productions were repeated by each subject on a second test day. The SNL differences between repeated test samples (different days) were not statistically significant for any subject group. For the vowel samples produced at a comfortable pitch, a relatively large SNL was associated with samples phonated by the subjects of each sex who manifested the relatively low singing pitch range. Regarding the vowel samples produced at the assigned-pitch levels, it was found that both vowel SNL and perceived vowel roughness decreased as test-pitch level was raised over a range of one octave. The relationship between vocal pitch and either vowel roughness or SNL approached linearity for each of the four subject groups.     

Update on paediatric tracheostomy tubes.

In the recent past there has been a significant expansion in the range of paediatric tracheostomy tubes available. This has mainly been in response to clinicians' requests. This article reviews those now available and the situations in which they are useful. A sizing chart is included for easy reference.     

Speech and phonological characteristics of individual children with a history of tracheostomy.

The present investigation studied the speech production and phonological skills of 6 children between the ages of 2;8 and 6;8 (years;months) who had undergone tracheostomy before age 8 months. Each child's speech was analyzed for size and composition of phonetic inventory, use of phonological processes, production of vowels, and production of the voicing contrast for stops. Analyses were completed once consistent air support for vocalization was established for each child and 3 months after that date. This study highlights the slow development of sound acquisition, vowel production, and the distinction between voiced and voiceless stops for some, but not all, children with a history of tracheostomy. Each child exhibited his or her own pattern of speech production difficulties on four tasks. Excessive use of inappropriate phonological processes relative to age was the most prevalent speech production problem. Five of 6 subjects exhibited clinically significant use of Stridency Deletion, Liquid Deviation, and/or Cluster Reduction. Adjustments were noted in the speech of all subjects during a 3-month period.     

Adults' perception and production of the English vowel /i/.

This study investigated the link between the perception and production of the English vowel /i/ by adult native speakers of English. Participants first produced the vowel /i/ using normal (citation) and careful (hyperarticulated) speech, then completed a method of adjustment task in which they selected their ideal exemplar of /i/. In this perceptual task, 24 of 35 participants had a prototype; the remaining 11 did not, but were retained for comparison. In keeping with the hyperspace effect (K. Johnson, E. Flemming, & R. Wright, 1993), all participants selected perceptual stimuli with F1 and F2 values that were more extreme (i.e., higher and further forward in the vowel space) than those of their normal, citation productions. An analysis of front-back and high-low qualities for the perceptual and production data in Euclidian space revealed that hyperarticulated speech was closer to the perceptual data than citation speech was, but only for participants with relatively clear-cut prototypes. The basis for such individual variation in perception-production links is discussed.