Speech disruption during delayed auditory feedback with simultaneous visual feedback

Delayed auditory feedback (DAF) regarding speech can cause dysfluency. The purpose of this study was to explore whether providing visual feedback in addition to DAF would ameliorate speech disruption. Speakers repeated sentences and heard their auditory feedback delayed with and without simultaneous visual feedback. DAF led to increased sentence durations and an increased number of speech disruptions. Although visual feedback did not reduce DAF effects on duration, a promising but nonsignificant trend was observed for fewer speech disruptions when visual feedback was provided. This trend was significant in speakers who were overall less affected by DAF. The results suggest the possibility that speakers strategically use alternative sources of feedback.     

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.     

Learning to use an artificial visual cue in speech identification

Visual information from a speaker's face profoundly influences auditory perception of speech. However, relatively little is known about the extent to which visual influences may depend on experience, and extent to which new sources of visual speech information can be incorporated in speech perception. In the current study, participants were trained on completely novel visual cues for phonetic categories. Participants learned to accurately identify phonetic categories based on novel visual cues. These newly-learned visual cues influenced identification responses to auditory speech stimuli, but not to the same extent as visual cues from a speaker's face. The novel methods and results of the current study raise theoretical questions about the nature of information integration in speech perception, and open up possibilities for further research on learning in multimodal perception, which may have applications in improving speech comprehension among the hearing-impaired.     

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.     

Young cochlear implant users' response to delayed auditory feedback.

This investigation determined whether the signal provided by the Cochlear Corporation Nucleus cochlear implant can convey enough speech information to induce a response to delayed auditory feedback (DAF), and whether prelingually deafened children who received a cochlear implant relatively late in their speech development are susceptible. Ten children with the Nucleus cochlear implant spoke simple phrases, first without and then with DAF. Three prelingually deafened subjects and the only two postlingually deafened subjects demonstrated longer phrase durations when speaking with DAF than without it. Two of the prelingually deafened subjects who demonstrated a response received their cochlear implants at the age of 5 years.     

Integration efficiency for speech perception within and across sensory modalities by normal-hearing and hearing-impaired individuals

In face-to-face speech communication, the listener extracts and integrates information from the acoustic and optic speech signals. Integration occurs within the auditory modality (i.e., across the acoustic frequency spectrum) and across sensory modalities (i.e., across the acoustic and optic signals). The difficulties experienced by some hearing-impaired listeners in understanding speech could be attributed to losses in the extraction of speech information, the integration of speech cues, or both. The present study evaluated the ability of normal-hearing and hearing-impaired listeners to integrate speech information within and across sensory modalities in order to determine the degree to which integration efficiency may be a factor in the performance of hearing-impaired listeners. Auditory-visual nonsense syllables consisting of eighteen medial consonants surrounded by the vowel [a] were processed into four nonoverlapping acoustic filter bands between 300 and 6000 Hz. A variety of one, two, three, and four filter-band combinations were presented for identification in auditory-only and auditory-visual conditions: A visual-only condition was also included. Integration efficiency was evaluated using a model of optimal integration. Results showed that normal-hearing and hearing-impaired listeners integrated information across the auditory and visual sensory modalities with a high degree of efficiency, independent of differences in auditory capabilities. However, across-frequency integration for auditory-only input was less efficient for hearing-impaired listeners. These individuals exhibited particular difficulty extracting information from the highest frequency band (4762-6000 Hz) when speech information was presented concurrently in the next lower-frequency band (1890-2381 Hz). Results suggest that integration of speech information within the auditory modality, but not across auditory and visual modalities, affects speech understanding in hearing-impaired listeners.     

Timing interference to speech in altered listening conditions

A theory is outlined that explains the disruption that occurs when auditory feedback is altered. The key part of the theory is that the number of, and relationship between, inputs to a timekeeper, operative during speech control, affects speech performance. The effects of alteration to auditory feedback depend on the extra input provided to the timekeeper. Different disruption is predicted for auditory feedback that is out of synchrony with other speech activity (e.g., delayed auditory feedback, DAF) compared with synchronous forms of altered feedback (e.g., frequency shifted feedback, FSF). Stimulus manipulations that can be made synchronously with speech are predicted to cause equivalent disruption to the synchronous form of altered feedback. Three experiments are reported. In all of them, subjects repeated a syllable at a fixed rate (Wing and Kristofferson, 1973). Overall timing variance was decomposed into the variance of a timekeeper (Cv) and the variance of a motor process (Mv). Experiment 1 validated Wing and Kristofferson's method for estimating Cv in a speech task by showing that only this variance component increased when subjects repeated syllables at different rates. Experiment 2 showed DAF increased Cv compared with when no altered sound occurred (experiment 1) and compared with FSF. In experiment 3, sections of the subject's output sequence were increased in amplitude. Subjects just heard this sound in one condition and made a duration decision about it in a second condition. When no response was made, results were like those with FSF. When a response was made, Cv increased at longer repetition periods. The findings that the principal effect of DAF, a duration decision and repetition period is on Cv whereas synchronous alterations that do not require a decision (amplitude increased sections where no response was made and FSF) do not affect Cv, support the hypothesis that the timekeeping process is affected by synchronized and asynchronized inputs in different ways.     

Adaptive auditory feedback control of the production of formant trajectories in the Mandarin triphthong /iau/ and its pattern of generalization

In order to test whether auditory feedback is involved in the planning of complex articulatory gestures in time-varying phonemes, the current study examined native Mandarin speakers' responses to auditory perturbations of their auditory feedback of the trajectory of the first formant frequency during their production of the triphthong /iau/. On average, subjects adaptively adjusted their productions to partially compensate for the perturbations in auditory feedback. This result indicates that auditory feedback control of speech movements is not restricted to quasi-static gestures in monophthongs as found in previous studies, but also extends to time-varying gestures. To probe the internal structure of the mechanisms of auditory-motor transformations, the pattern of generalization of the adaptation learned on the triphthong /iau/ to other vowels with different temporal and spatial characteristics (produced only under masking noise) was tested. A broad but weak pattern of generalization was observed; the strength of the generalization diminished with increasing dissimilarity from /iau/. The details and implications of the pattern of generalization are examined and discussed in light of previous sensorimotor adaptation studies of both speech and limb motor control and a neurocomputational model of speech motor control.     

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.     

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.     

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.     

Compensatory responses to loudness-shifted voice feedback during production of Mandarin speech

Previous studies have demonstrated that perturbations in voice pitch or loudness feedback lead to compensatory changes in voice F(0) or amplitude during production of sustained vowels. Responses to pitch-shifted auditory feedback have also been observed during English and Mandarin speech. The present study investigated whether Mandarin speakers would respond to amplitude-shifted feedback during meaningful speech production. Native speakers of Mandarin produced two-syllable utterances with focus on the first syllable, the second syllable, or none of the syllables, as prompted by corresponding questions. Their acoustic speech signal was fed back to them with loudness shifted by +/-3 dB for 200 ms durations. The responses to the feedback perturbations had mean latencies of approximately 142 ms and magnitudes of approximately 0.86 dB. Response magnitudes were greater and latencies were longer when emphasis was placed on the first syllable than when there was no emphasis. Since amplitude is not known for being highly effective in encoding linguistic contrasts, the fact that subjects reacted to amplitude perturbation just as fast as they reacted to F(0) perturbations in previous studies provides clear evidence that a highly automatic feedback mechanism is active in controlling both F(0) and amplitude of speech production.     

Vowel and consonant recognition of cochlear implant patients using formant-estimating speech processors

Vowel and consonant confusion matrices were collected in the hearing alone (H), lipreading alone (L), and hearing plus lipreading (HL) conditions for 28 patients participating in the clinical trial of the multiple-channel cochlear implant. All patients were profound-to-totally deaf and "hearing" refers to the presentation of auditory information via the implant. The average scores were 49% for vowels and 37% for consonants in the H condition and the HL scores were significantly higher than the L scores. Information transmission and multidimensional scaling analyses showed that different speech features were conveyed at different levels in the H and L conditions. In the HL condition, the visual and auditory signals provided independent information sources for each feature. For vowels, the auditory signal was the major source of duration information, while the visual signal was the major source of first and second formant frequency information. The implant provided information about the amplitude envelope of the speech and the estimated frequency of the main spectral peak between 800 and 4000 Hz, which was useful for consonant recognition. A speech processor that coded the estimated frequency and amplitude of an additional peak between 300 and 1000 Hz was shown to increase the vowel and consonant recognition in the H condition by improving the transmission of first formant and voicing information.     

The effect of superior auditory skills on vocal accuracy

The relationship between auditory perception and vocal production has been typically investigated by evaluating the effect of either altered or degraded auditory feedback on speech production in either normal hearing or hearing-impaired individuals. Our goal in the present study was to examine this relationship in individuals with superior auditory abilities. Thirteen professional musicians and thirteen nonmusicians, with no vocal or singing training, participated in this study. For vocal production accuracy, subjects were presented with three tones. They were asked to reproduce the pitch using the vowel /a/. This procedure was repeated three times. The fundamental frequency of each production was measured using an autocorrelation pitch detection algorithm designed for this study. The musicians' superior auditory abilities (compared to the nonmusicians) were established in a frequency discrimination task reported elsewhere. Results indicate that (a) musicians had better vocal production accuracy than nonmusicians (production errors of 1/2 a semitone compared to 1.3 semitones, respectively); (b) frequency discrimination thresholds explain 43% of the variance of the production data, and (c) all subjects with superior frequency discrimination thresholds showed accurate vocal production; the reverse relationship, however, does not hold true. In this study we provide empirical evidence to the importance of auditory feedback on vocal production in listeners with superior auditory skills.     

Relative timing characteristics of hearing-impaired speakers.

Speech duration characteristics of phrase-level utterances produced by 26 severely and profoundly hearing-impaired adults were examined acoustically using relative timing measures. The measures were then compared to the same utterances produced by 13 normal-hearing adults. Although absolute speech durations of the hearing-impaired subjects were significantly longer than their normal-hearing counterparts, relative timing did not differ between groups. Findings are discussed in relation to the biological constraint hypothesis associated with speech timing, as well as the role of auditory feedback in models of speech production.     

The effects of auditory feedback on the regulation of intraoral air pressure during speech.

Previous experimental evidence has been interpreted as support for regulation of both acoustics and aerodynamics during speech production. One recent perspective is that although speech acoustics may be manipulated, regulation of aerodynamics is a central component of the processes that produce speech. From this perspective, it has been suggested that aerodynamic regulation is given priority over perceptual accuracy. The experiment attempted to test this hypothesis by forcing speakers into a choice between aerodynamic and acoustic regulation. The intensity level of frication (embedded in a carrier phrase) was selectively amplified or attenuated and fed back to the speaker on line. Intraoral air pressure was recorded in order to assess whether or not perturbed auditory feedback would result in aerodynamic compensation. Although compensatory changes in peak intraoral air pressure, pressure duration, and pressure curve area were seen in response to 30-dB alterations of frication, no systematic effects were seen for smaller auditory manipulations. Further, the compensations were less than what one might expect from a system controlling auditory output. Explanations of these findings and their implications for the control of speech production are offered.     

Tactile enhancement of auditory and visual speech perception in untrained perceivers

A single pool of untrained subjects was tested for interactions across two bimodal perception conditions: audio-tactile, in which subjects heard and felt speech, and visual-tactile, in which subjects saw and felt speech. Identifications of English obstruent consonants were compared in bimodal and no-tactile baseline conditions. Results indicate that tactile information enhances speech perception by about 10 percent, regardless of which other mode (auditory or visual) is active. However, within-subject analysis indicates that individual subjects who benefit more from tactile information in one cross-modal condition tend to benefit less from tactile information in the other.     

Compensation following real-time manipulation of formants in isolated vowels

Auditory feedback influences human speech production, as demonstrated by studies using rapid pitch and loudness changes. Feedback has also been investigated using the gradual manipulation of formants in adaptation studies with whispered speech. In the work reported here, the first formant of steady-state isolated vowels was unexpectedly altered within trials for voiced speech. This was achieved using a real-time formant tracking and filtering system developed for this purpose. The first formant of vowel /epsilon/ was manipulated 100% toward either /ae/ or /I/, and participants responded by altering their production with average Fl compensation as large as 16.3% and 10.6% of the applied formant shift, respectively. Compensation was estimated to begin <460 ms after stimulus onset. The rapid formant compensations found here suggest that auditory feedback control is similar for both F0 and formants.     

Acoustic analysis of monophthong and diphthong production in acquired severe to profound hearing loss

The effect of diminished auditory feedback on monophthong and diphthong production was examined in postlingually deafened Australian-English speaking adults. The participants were 4 female and 3 male speakers with severe to profound hearing loss, who were compared to 11 age- and accent-matched normally hearing speakers. The test materials were 5 repetitions of hVd words containing 18 vowels. Acoustic measures that were studied included F1, F2, discrete cosine transform coefficients (DCTs), and vowel duration information. The durational analyses revealed increased total vowel durations with a maintenance of the tense/lax vowel distinctions in the deafened speakers. The deafened speakers preserved a differentiated vowel space, although there were some gender-specific differences seen. For example, there was a retraction of F2 in the front vowels for the female speakers that did not occur in the males. However, all deafened speakers showed a close correspondence between the monophthong and diphthong formant movements that did occur. Gaussian classification highlighted vowel confusions resulting from changes in the deafened vowel space. The results support the view that postlingually deafened speakers maintain reasonably good speech intelligibility, in part by employing production strategies designed to bolster auditory feedback.     

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.