Interactions of speaking condition and auditory feedback on vowel production in postlingually deaf adults with cochlear implants

This study investigates the effects of speaking condition and auditory feedback on vowel production by postlingually deafened adults. Thirteen cochlear implant users produced repetitions of nine American English vowels prior to implantation, and at one month and one year after implantation. There were three speaking conditions (clear, normal, and fast), and two feedback conditions after implantation (implant processor turned on and off). Ten normal-hearing controls were also recorded once. Vowel contrasts in the formant space (expressed in mels) were larger in the clear than in the fast condition, both for controls and for implant users at all three time samples. Implant users also produced differences in duration between clear and fast conditions that were in the range of those obtained from the controls. In agreement with prior work, the implant users had contrast values lower than did the controls. The implant users' contrasts were larger with hearing on than off and improved from one month to one year postimplant. Because the controls and implant users responded similarly to a change in speaking condition, it is inferred that auditory feedback, although demonstrably important for maintaining normative values of vowel contrasts, is not needed to maintain the distinctiveness of those contrasts in different speaking conditions.     

The effects of tongue loading and auditory feedback on vowel production

This study investigated the role of sensory feedback during the production of front vowels. A temporary aftereffect induced by tongue loading was employed to modify the somatosensory-based perception of tongue height. Following the removal of tongue loading, tongue height during vowel production was estimated by measuring the frequency of the first formant (F1) from the acoustic signal. In experiment 1, the production of front vowels following tongue loading was investigated either in the presence or absence of auditory feedback. With auditory feedback available, the tongue height of front vowels was not modified by the aftereffect of tongue loading. By contrast, speakers did not compensate for the aftereffect of tongue loading when they produced vowels in the absence of auditory feedback. In experiment 2, the characteristics of the masking noise were manipulated such that it masked energy either in the F1 region or in the region of the second and higher formants. The results showed that the adjustment of tongue height during the production of front vowels depended on information about F1 in the auditory feedback. These findings support the idea that speech goals include both auditory and somatosensory targets and that speakers are able to make use of information from both sensory modalities to maximize the accuracy of speech production.     

Vowel recognition via cochlear implants and noise vocoders: effects of formant movement and duration

Previous work has demonstrated that normal-hearing individuals use fine-grained phonetic variation, such as formant movement and duration, when recognizing English vowels. The present study investigated whether these cues are used by adult postlingually deafened cochlear implant users, and normal-hearing individuals listening to noise-vocoder simulations of cochlear implant processing. In Experiment 1, subjects gave forced-choice identification judgments for recordings of vowels that were signal processed to remove formant movement and/or equate vowel duration. In Experiment 2, a goodness-optimization procedure was used to create perceptual vowel space maps (i.e., best exemplars within a vowel quadrilateral) that included F1, F2, formant movement, and duration. The results demonstrated that both cochlear implant users and normal-hearing individuals use formant movement and duration cues when recognizing English vowels. Moreover, both listener groups used these cues to the same extent, suggesting that postlingually deafened cochlear implant users have category representations for vowels that are similar to those of normal-hearing individuals.     

Effect of different types of auditory stimulation on vowel formant frequencies in multichannel cochlear implant users

Two experiments investigating the effects of auditory stimulation delivered via a Nucleus multichannel cochlear implant upon vowel production in adventitiously deafened adult speakers are reported. The first experiment contrasts vowel formant frequencies produced without auditory stimulation (implant processor OFF) to those produced with auditory stimulation (processor ON). Significant shifts in second formant frequencies were observed for intermediate vowels produced without auditory stimulation; however, no significant shifts were observed for the point vowels. Higher first formant frequencies occurred in five of eight vowels when the processor was turned ON versus OFF. A second experiment contrasted productions of the word "head" produced with a FULL map, OFF condition, and a SINGLE channel condition that restricted the amount of auditory information received by the subjects. This experiment revealed significant shifts in second formant frequencies between FULL map utterances and the other conditions. No significant differences in second formant frequencies were observed between SINGLE channel and OFF conditions. These data suggest auditory feedback information may be used to adjust the articulation of some speech sounds.     

The effect of partially restored hearing on speech production of postlingually deafened adults with multichannel cochlear implants

The effect of auditory feedback on speech production was investigated in five postlingually deafened adults implanted with the 22-channel Nucleus device. Changes in speech production were measured before implant and 1, 6, and 24 months postimplant. Acoustic measurements included: F1 and F2 of vowels in word-in-isolation and word-in-sentence context, voice-onset-time (VOT), spectral range of sibilants, fundamental frequency (F0) of word-in-isolation and word-in-sentence context, and word and sentence duration. Perceptual ratings of speech quality were done by ten listeners. The significant changes after cochlear implantation included: a decrease of F0, word and sentence duration, and F1 values, and an increase of voiced plosives' voicing lead (from positive to negative VOT values) and fricatives' spectral range. Significant changes occurred until 2 years postimplant when most measured values fell within Hebrew norms. Listeners were found to be sensitive to the acoustic changes in the speech from preimplant to 1, 6, and 24 months postimplant. Results suggest that when hearing is restored in postlingually deafened adults, calibration of speech is not immediate and occurs over time depending on the age-at-onset of deafness, years of deafness, and perception skills. The results also concur with hypothesis that the observed changes of some speech parameters are an indirect consequence of intentional changes in other articulatory parameters.     

Sensorimotor adaptation to feedback perturbations of vowel acoustics and its relation to perception

The role of auditory feedback in speech motor control was explored in three related experiments. Experiment 1 investigated auditory sensorimotor adaptation: the process by which speakers alter their speech production to compensate for perturbations of auditory feedback. When the first formant frequency (F1) was shifted in the feedback heard by subjects as they produced vowels in consonant-vowel-consonant (CVC) words, the subjects' vowels demonstrated compensatory formant shifts that were maintained when auditory feedback was subsequently masked by noise-evidence of adaptation. Experiment 2 investigated auditory discrimination of synthetic vowel stimuli differing in F1 frequency, using the same subjects. Those with more acute F1 discrimination had compensated more to F1 perturbation. Experiment 3 consisted of simulations with the directions into velocities of articulators model of speech motor planning, which showed that the model can account for key aspects of compensation. In the model, movement goals for vowels are regions in auditory space; perturbation of auditory feedback invokes auditory feedback control mechanisms that correct for the perturbation, which in turn causes updating of feedforward commands to incorporate these corrections. The relation between speaker acuity and amount of compensation to auditory perturbation is mediated by the size of speakers' auditory goal regions, with more acute speakers having smaller goal regions.     

Vowel spaces in Swedish adolescents with cochlear implants

This paper examines vowel production in Swedish adolescents with cochlear implants. Twelve adolescents with cochlear implants and 11 adolescents with normal hearing participated. Measurements were made of the first and second formants in all the nine long Swedish vowels. The values in hertz were bark-transformed, and two measures of the size of the vowel space were obtained. The first of them was the average Euclidean distance in the F1-F2 plane between the nine vowels and the mean F1 and F2 values of all the vowels. The second was the mean Euclidean distance in the F1-F2 plane between all the vowels. The results showed a significant difference for both vowel space measures between the two groups of adolescents. The cochlear implant users had a smaller space than the adolescents with normal hearing. In general, the size of the vowel space showed no correlations with measures of receptive and productive linguistic abilities. However, the results of an identification test showed that the listeners made more confusions of the vowels produced by speakers who had a small mean distance in the F1-F2 plane between all the vowels.     

Speech of cochlear implant patients: a longitudinal study of vowel production.

Acoustic parameters were measured for vowels spoken in /hVd/ context by four postlingually deafened recipients of multichannel (Ineraid) cochlear implants. Three of the subjects became totally deaf in adulthood after varying periods of partial hearing loss; the fourth became totally deaf at age four. The subjects received different degrees of perceptual benefit from the prosthesis. Recordings were made before, and at intervals following speech processor activation. The measured parameters included F1, F2, F0, SPL, duration, and amplitude difference between the first two harmonic peaks in the log magnitude spectrum (H 1-H2). Numerous changes in parameter values were observed from pre- to post-implant, with differences among subjects. Many changes, but not all, were in the direction of normative data, and most changes were consistent with hypotheses about relations among the parameters. Some of the changes tended to enhance phonemic contrasts; others had the opposite effect. For three subjects, H 1-H2 changed in a direction consistent with measurements of their average air flow when reading; that relation was more complex for the fourth subject. The results are interpreted with respect to: characteristics of the individual subjects, including vowel identification scores; mechanical interactions among glottal and supraglottal articulations; and hypotheses about the role of auditory feedback in the control of speech production. Almost all the observed differences could be attributed to changes in the average settings of speaking rate, F0 and SPL, which presumably can be perceived without the need for spectral place information. Some observed F2 realignment may be attributable to the reception of spectral cues.     

Probing the independence of formant control using altered auditory feedback

Two auditory feedback perturbation experiments were conducted to examine the nature of control of the first two formants in vowels. In the first experiment, talkers heard their auditory feedback with either F1 or F2 shifted in frequency. Talkers altered production of the perturbed formant by changing its frequency in the opposite direction to the perturbation but did not produce a correlated alteration of the unperturbed formant. Thus, the motor control system is capable of fine-grained independent control of F1 and F2. In the second experiment, a large meta-analysis was conducted on data from talkers who received feedback where both F1 and F2 had been perturbed. A moderate correlation was found between individual compensations in F1 and F2 suggesting that the control of F1 and F2 is processed in a common manner at some level. While a wide range of individual compensation magnitudes were observed, no significant correlations were found between individuals' compensations and vowel space differences. Similarly, no significant correlations were found between individuals' compensations and variability in normal vowel production. Further, when receiving normal auditory feedback, most of the population exhibited no significant correlation between the natural variation in production of F1 and F2.     

Speech changes following reimplantation from a single-channel to a multichannel cochlear implant.

The speech of a postlingually deafened preadolescent was recorded and analyzed while a single-electrode cochlear implant (3M/House) was in operation, on two occasions after it failed (1 day and 18 days) and on three occasions after stimulation of a multichannel cochlear implant (Nucleus 22) (1 day, 6 months, and 1 year). Listeners judged 3M/House tokens to be the most normal until the subject had one year's experience with the Nucleus device. Spectrograms showed less aspiration, better formant definition and longer final frication and closure duration post-Nucleus stimulation (6 MO. NUCLEUS and 1 YEAR NUCLEUS) relative to the 3M/House and no auditory feedback conditions. Acoustic measurements after loss of auditory feedback (1 DAY FAIL and 18 DAYS FAIL) indicated a constriction of vowel space. Appropriately higher fundamental frequency for stressed than unstressed syllables, an expansion of vowel space and improvement in some aspects of production of voicing, manner and place of articulation were noted one year post-Nucleus stimulation. Loss of auditory feedback results are related to the literature on the effects of postlingual deafness on speech. Nucleus and 3M/House effects on speech are discussed in terms of speech production studies of single-electrode and multichannel patients.     

Effects of postlingual deafness on speech production: implications for the role of auditory feedback

This study investigated some effects of postlingual deafness on speech by exploring selected properties of consonants, vowels, and suprasegmentals in the speech of seven totally, postlingually deafened individuals. The observed speech properties included parameters that function as phonological contrasts in English, as well as parameters that constitute primarily phonetic distinctions. The results demonstrated that postlingual deafness affects the production of all classes of speech sounds, suggesting that auditory feedback is implicated in regulating the phonetic precision of consonants, vowels, and suprasegmentals over the long term. In addition, the results are discussed in relation to factors that may influence the degree of speech impairment, such as age at onset of deafness.     

Perceptuomotor bias in the imitation of steady-state vowels

Previous studies suggest that speakers are systematically inaccurate, or biased, when imitating self-produced vowels. The direction of these biases in formant space and their variation may offer clues about the organization of the vowel perceptual space. To examine these patterns, three male speakers were asked to imitate 45 self-produced vowels that were systematically distributed in F1/F2 space. All three speakers showed imitation bias, and the bias magnitudes were significantly larger than those predicted by a model of articulatory noise. Each speaker showed a different pattern of bias directions, but the pattern was unrelated to the locations of prototypical vowels produced by that speaker. However, there were substantial quantitative regularities: (1) The distribution of imitation variability and bias magnitudes were similar for all speakers, (2) the imitation variability was independent of the bias magnitudes, and (3) the imitation variability (a production measure) was commensurate with the formant discrimination limen (a perceptual measure). These results indicate that there is additive Gaussian noise in the imitation process that independently affects each formant and that there are speaker-dependent and potentially nonlinguistic biases in vowel perception and production.     

Formant frequencies in Estonian folk singing.

Formant frequencies in an old Estonian folk song performed by two female voices were estimated for two back vowels /a/ and /u/, and for two front vowels /e/ and /i/. Comparison of these estimates with formant frequencies in spoken Estonian vowels indicates a trend of the vowels to be clustered into two sets of front and back ones in the F1/F2 plane. Similar clustering has previously been shown to occur in opera and choir singing, especially with increasing fundamental frequency. The clustering in the present song, however, may also be due to a tendency for a mid vowel to be realized as a higher-beginning diphthong, which is characteristic of the North-Estonian coastal dialect area where the singers come from. No evidence of a "singer's formant" was found.     

Acoustic evidence for dynamic formant trajectories in Australian English vowels.

The extent to which it is necessary to model the dynamic behavior of vowel formants to enable vowel separation has been the subject of debate in recent years. To investigate this issue, a study has been made on the vowels of 132 Australian English speakers (male and female). The degree of vowel separation from the formant values at the target was contrasted to that from modeling the formant contour with discrete cosine transform coefficients. The findings are that, although it is necessary to model the formant contour to separate out the diphthongs, the formant values at the target, plus vowel duration are sufficient to separate out the monophthongs. However, further analysis revealed that there are formant contour differences which benefit the within-class separation of the tense/lax monophthong pairs.     

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.     

The influence of final-syllable position on the vowel and word duration of deaf talkers

Hearing talkers produce shorter vowel and word durations in multisyllabic contexts than in monosyllabic contexts. This investigation determined whether a similar effect occurs for deaf talkers, a population often characterized as lacking coarticulation in their speech. Four prelingually deafened adults and two hearing controls produced three sets of word sequences. Each set included a kernel word and six derived forms (e.g., "speed," "speedy," "speeding," etc.). The derived forms were created by adding unstressed and stressed syllables to the kernel form. A spectrographic analysis indicated that the deaf subjects did not always decrease word and vowel durations for the derivatives. Unlike hearing speakers, they often did not reduce vowel segments more than consonant segments. Three explanations are forwarded for the shortening effects. One relates to the implementation of temporal rules, the second concerns the organization imposed upon the articulators to produce speech, and the third suggests a language-independent vocal tract characteristic. The role of auditory information in developing the shortening effects is also considered.     

A cross-language study of compensation in response to real-time formant perturbation

Past studies have shown that when formants are perturbed in real time, speakers spontaneously compensate for the perturbation by changing their formant frequencies in the opposite direction to the perturbation. Further, the pattern of these results suggests that the processing of auditory feedback error operates at a purely acoustic level. This hypothesis was tested by comparing the response of three language groups to real-time formant perturbations, (1) native English speakers producing an English vowel /ε/, (2) native Japanese speakers producing a Japanese vowel (/e([inverted perpendicular])/), and (3) native Japanese speakers learning English, producing /ε/. All three groups showed similar production patterns when F1 was decreased; however, when F1 was increased, the Japanese groups did not compensate as much as the native English speakers. Due to this asymmetry, the hypothesis that the compensatory production for formant perturbation operates at a purely acoustic level was rejected. Rather, some level of phonological processing influences the feedback processing behavior.     

Consonant influences on vowel duration as a function of speech intelligibility for hearing-impaired individuals

The purpose of this investigation was to study the effects of consonant environment on vowel duration for normally hearing males, hearing-impaired males with intelligible speech, and hearing-impaired males with semi-intelligible speech. The results indicated that the normally hearing and intelligible hearing-impaired speakers exhibited similar trends with respect to consonant influence on vowel duration; i.e., vowels were longer in duration, in a voiced environment as compared with a voiceless, and in a fricative environment as compared with a plosive. The semi-intelligible hearing-impaired speakers, however, failed to demonstrate a consonant effect on vowel duration, and produced the vowels with significantly longer durations when compared with the other two groups of speakers. These data provide information regarding temporal conditions which may contribute to the decreased intelligibility of hearing-impaired persons.     

Effects of Tonsillectomy on Speech Spectrum

Changes in the speech spectrum of vowels and consonants before and after tonsillectomy were investigated to find out the impact of the operation on speech quality. Speech recordings obtained from patients were analyzed using the Kay Elemetrics, Multi-Dimensional Voice Processing (MDVP Advanced) software. Examination of the time-course changes after the operation revealed that certain speech parameters changed. These changes were mainly F3 (formant center frequency) and B3 (formant bandwidth) for the vowel /o/ and a slight decrease in B1 and B2 for the vowel /a/. The noise-to-harmonic ratio (NHR) also decreased slightly, suggesting less nasalized vowels. It was also observed that the fricative, glottal consonant /h/ has been affected. The larger the tonsil had been, the more changes were seen in the speech spectrum. The changes in the speech characteristics (except F3 and B3 for the vowel /o/) tended to recover, suggesting an involvement of auditory feedback and/or replacement of a new soft tissue with the tonsils. Although the changes were minimal and, therefore, have little effect on the extracted acoustic parameters, they cannot be disregarded for those relying on their voice for professional reasons, that is, singers, professional speakers, and so forth.     

Multimodal Standardization of Voice Among Four Multicultural Populations Formant Structures

A stratified random sample of 20 males and 20 females matched for physiologic factors and cultural-linguistic markers was examined to determine differences in formant frequencies during prolongation of three vowels: [a], [i], and [u]. The ethnic and gender breakdown included four sets of 5 male and 5 female subjects comprised of Caucasian and African American speakers of Standard American English, native Hindi Indian speakers, and native Mandarin Chinese speakers. Acoustic measures were analyzed using the Computerized Speech Lab (4300B) from which formant histories were extracted from a 200-ms sample of each vowel token to obtain first formant (F1), second formant (F2), and third formant (F3) frequencies. Significant group differences for the main effect of culture and race were found. For the main effect gender, sexual dimorphism in vowel formants was evidenced for all cultures and races across all three vowels. The acoustic differences found are attributed to cultural-linguistic factors.