Compensatory and adaptive responses to real-time formant shifts in adults and children

Auditory feedback plays an important role in speech motor learning. Previous studies investigating auditory feedback in speech development suggest that crucial steps are made in the development of auditory-motor integration around the age of 4. The present study investigated compensatory and adaptive responses to auditory perturbation in 4 to 9 year-old children compared to young adults (aged 19 – 29 years). Auditory feedback was perturbed by real-time shifting the first and second formant (F1 and F2) of the vowel /e:/ during the production of CVC words in a fivestep paradigm (familiarization; baseline; ramp; hold; release). Results showed that the children were able to compensate and adapt in a similar or larger degree compared to the young adults, even though the proportion of speakers displaying a consistent compensatory response was higher in the group of adults. In contrast to previous reports, results did not show differences in token-to-token variability between children and adults

Exploring auditory-motor interactions in normal and disordered speech

Auditory feedback plays an important role in speech motor learning and in the online correction of speech movements. Speakers can detect and correct auditory feedback errors at the segmental and suprasegmental levels during ongoing speech. The frontal brain regions that contribute to these corrective movements have also been shown to be more active during speech in persons who stutter (PWS) compared to fluent speakers. Further, various types of altered auditory feedback can temporarily improve the fluency of PWS, suggesting that atypical auditory-motor interactions during speech may contribute to stuttering disfluencies. To investigate this possibility, we have developed and improved Audapter, a software that enables configurable dynamic perturbation of the spatial and temporal content of the speech auditory signal in real time. Using Audapter, we have measured the compensatory responses of PWS to static and dynamic perturbations of the formant content of auditory feedback and compared these responses with those from matched fluent controls. Our findings indicate deficient utilization of auditory feedback by PWS for short-latency online control of the spatial and temporal parameters of articulation during vowel production and during running speech. These findings provide further evidence that stuttering is associated with aberrant auditory-motor integration during speech.Published versio

Pediatric Responses to Fundamental and Formant Frequency Altered Auditory Feedback: A Scoping Review

Purpose: The ability to hear ourselves speak has been shown to play an important role in the development and maintenance of fluent and coherent speech. Despite this, little is known about the developing speech motor control system throughout childhood, in particular if and how vocal and articulatory control may differ throughout development. A scoping review was undertaken to identify and describe the full range of studies investigating responses to frequency altered auditory feedback in pediatric populations and their contributions to our understanding of the development of auditory feedback control and sensorimotor learning in childhood and adolescence. Method: Relevant studies were identified through a comprehensive search strategy of six academic databases for studies that included (a) real-time perturbation of frequency in auditory input, (b) an analysis of immediate effects on speech, and (c) participants aged 18 years or younger. Results: Twenty-three articles met inclusion criteria. Across studies, there was a wide variety of designs, outcomes and measures used. Manipulations included fundamental frequency (9 studies), formant frequency (12), frequency centroid of fricatives (1), and both fundamental and formant frequencies (1). Study designs included contrasts across childhood, between children and adults, and between typical, pediatric clinical and adult populations. Measures primarily explored acoustic properties of speech responses (latency, magnitude, and variability). Some studies additionally examined the association of these acoustic responses with clinical measures (e.g., stuttering severity and reading ability), and neural measures using electrophysiology and magnetic resonance imaging. Conclusion: Findings indicated that children above 4 years generally compensated in the opposite direction of the manipulation, however, in several cases not as effectively as adults. Overall, results varied greatly due to the broad range of manipulations and designs used, making generalization challenging. Differences found between age groups in the features of the compensatory vocal responses, latency of responses, vocal variability and perceptual abilities, suggest that maturational changes may be occurring in the speech motor control system, affecting the extent to which auditory feedback is used to modify internal sensorimotor representations. Varied findings suggest vocal control develops prior to articulatory control. Future studies with multiple outcome measures, manipulations, and more expansive age ranges are needed to elucidate findings

Brittany Bernal - Sensorimotor Adaptation of Speech Through a Virtually Shortened Vocal Tract

The broad objective of this line of research is to understand how auditory feedback manipulations may be used to elicit involuntary changes in speech articulation. We examine speech sensorimotor adaptation to supplement the development of speech rehabilitation applications that benefit from this learning phenomenon. By manipulating the acoustics of one’s auditory feedback, it is possible to elicit involuntary changes in speech articulation. We seek to understand how virtually manipulating participants’ perception of vowel space affects their speech movements by assessing acoustic variables such as formant frequency changes. Participants speak through a digital audio processing device that virtually alters the perceived size of their vocal tract. It is hypothesized that this modification to auditory feedback will facilitate adaptive changes in motor behavior as indicated by acoustic changes resulting from speech articulation. This study will determine how modifying the perception of vocal tract size affects articulatory behavior, indicated by changes in formant frequencies and changes in vowel space area. This work will also determine if and how the size of the virtual vowel space affects the magnitude and direction of sensorimotor adaptation for speech. The ultimate aim is to determine how important it is for the virtual vowel space to mimic the talker’s real vowel space, and whether or not perturbing the size of the perceived vowel space may facilitate or impede involuntary adaptive learning for speech. Sensorimotor Adaptation of Speech Through a Virtually Shortened Vocal Tract by Brittany Bernal is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.https://epublications.marquette.edu/mcnair_2014/1009/thumbnail.jp

Weak Responses to Auditory Feedback Perturbation during Articulation in Persons Who Stutter: Evidence for Abnormal Auditory-Motor Transformation

Previous empirical observations have led researchers to propose that auditory feedback (the auditory perception of self-produced sounds when speaking) functions abnormally in the speech motor systems of persons who stutter (PWS). Researchers have theorized that an important neural basis of stuttering is the aberrant integration of auditory information into incipient speech motor commands. Because of the circumstantial support for these hypotheses and the differences and contradictions between them, there is a need for carefully designed experiments that directly examine auditory-motor integration during speech production in PWS. In the current study, we used real-time manipulation of auditory feedback to directly investigate whether the speech motor system of PWS utilizes auditory feedback abnormally during articulation and to characterize potential deficits of this auditory-motor integration. Twenty-one PWS and 18 fluent control participants were recruited. Using a short-latency formant-perturbation system, we examined participants’ compensatory responses to unanticipated perturbation of auditory feedback of the first formant frequency during the production of the monophthong [ε]. The PWS showed compensatory responses that were qualitatively similar to the controls’ and had close-to-normal latencies (~150 ms), but the magnitudes of their responses were substantially and significantly smaller than those of the control participants (by 47% on average, p<0.05). Measurements of auditory acuity indicate that the weaker-than-normal compensatory responses in PWS were not attributable to a deficit in low-level auditory processing. These findings are consistent with the hypothesis that stuttering is associated with functional defects in the inverse models responsible for the transformation from the domain of auditory targets and auditory error information into the domain of speech motor commands

Altered Sensory Feedback in Speech

This chapter reviews the effects temporal, spectral and intensity perturbations to auditory and vibratory feedback have on fluent speakers and PWS. Early work on Delayed Auditory Feedback (DAF) with fluent speakers, showed that speech errors arise, speakers increase voice level, speech is slowed, medial vowels in syllables are elongated and pitch is monotone. It has been claimed that short-delay DAF produces effects on speech fluency, rate and naturalness that are as good as other forms of altered sensory feedback although this has been contested. Another alternative would be to reduce dosage by ramping intensity of altered auditory feedback down after a dysfluency provided speech is fluent and switch it to its full level when the next episode of stuttering occurs. Overall, temporal delays to speech feedback have a robust effect on fluent speakers and PWS. In fluent speakers, DAF induces a range of disruptions to speech

An Examination of the Factors that Dictate the Relative Weighting of Feedback and Feedforward Input for Speech Motor Control

Speech is arguably the most important form of human communication. Fluent speech production relies on auditory feedback for the planning, execution, and monitoring of speech movements. Auditory feedback is particularly important during the acquisition of speech, however, it has been suggested that over time speakers rely less on auditory feedback as they develop robust sensorimotor representations that allow speech motor commands to be executed in a feedforward manner. The studies reported in this thesis recorded speaker’s vocal and neural responses to altered auditory feedback in order to explore the factors that dictate the relative importance of auditory feedback for speech motor control. More specifically, studies 1 through 3 examined how the role of auditory feedback changes throughout development, while studies 4 and 5 examined the relationship between vocal variability and auditory feedback control, and lastly study 6 looked at how the predictability of auditory feedback errors influences the role of auditory feedback for speech motor control. Results of the first study demonstrated that toddlers use auditory feedback to regulate their speech motor commands, supporting the long held notion that auditory feedback is important during the acquisition of speech. While mapping out the developmental trajectory of vocal and event related potential responses to altered auditory feedback, the second study demonstrated that vocal variability, rather than age, best predicts responses to altered auditory feedback. Importantly, this suggests that the maturation of the speech motor control system is not strictly dependent on age. The third study in this thesis demonstrated that children and adults show similar rates of sensorimotor adaptation, suggesting that once speech is acquired, speakers are proficient at using sensory information to modify the planning of future speech motor commands. However, since adults produced larger compensatory responses, these results also suggested that adults are more proficient at comparing incoming auditory feedback with the feedback predicted by their sensorimotor representations, as a result of possessing more precisely mapped sensorimotor representations. The results of studies four and five demonstrated that vocal variability can be used to predict the size of compensatory responses and sensorimotor adaptation to changes in one’s auditory feedback, respectively. Furthermore, these studies demonstrated that increased variability was related to increased auditory feedback control of speech. Finally, the sixth study in this thesis demonstrated that experimentally induced predictability and variability can be used to induce increases in feedforward and auditory feedback control, respectively. In conclusion, the results reported in this thesis demonstrate that age and vocal variability, both naturally occurring and experimentally induced, are important determinants of the role of auditory feedback in speech motor control

Manipulation of Auditory Feedback in Individuals with Normal Hearing and Hearing Loss

Auditory feedback, the hearing of one’s own voice, plays an important role in the detection of speech errors and the regulation of speech production. The limited auditory cues available with a hearing loss can reduce the ability of individuals with hearing loss to use their auditory feedback. Hearing aids are a common assistive device that amplifies inaudible sounds. Hearing aids can also change auditory feedback through digital signal processing, such as frequency lowering. Frequency lowering moves high frequency information of an incoming auditory stimulus into a lower frequency region where audibility may be better. This can change how speech sounds are perceived. For example, the high frequency information of /s/ is moved closer to the lower frequency area of /ʃ/. As well, real-time signal processing in a laboratory setting can also manipulate various aspects of speech cues, such as intensity and vowel formants. These changes in auditory feedback may result in changes in speech production as the speech motor control system may perceive these perturbations as speech errors. A series of experiments were carried out to examine changes in speech production as a result of perturbations in the auditory feedback in individuals with normal hearing and hearing loss. Intensity and vowel formant perturbations were conducted using real-time signal processing in the laboratory. As well, changes in speech production were measured using auditory feedback that was processed with frequency lowering technology in hearing aids. Acoustic characteristics of intensity of vowels, sibilant fricatives, and first and second formants were analyzed. The results showed that the speech motor control system is sensitive to changes in auditory feedback because perturbations in auditory feedback can result in changes in speech production. However, speech production is not completely controlled by auditory feedback and other feedback systems, such as the somatosensory system, are also involved. An impairment of the auditory system can reduce the ability of the speech motor control system to use auditory feedback in the detection of speech errors, even when aided with hearing aids. Effects of frequency lowering in hearing aids on speech production depend on the parameters used and acclimatization time

Auditory-Motor Learning during Speech Production in 9-11-Year-Old Children

BACKGROUND: Hearing ability is essential for normal speech development, however the precise mechanisms linking auditory input and the improvement of speaking ability remain poorly understood. Auditory feedback during speech production is believed to play a critical role by providing the nervous system with information about speech outcomes that is used to learn and subsequently fine-tune speech motor output. Surprisingly, few studies have directly investigated such auditory-motor learning in the speech production of typically developing children. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, we manipulated auditory feedback during speech production in a group of 9-11-year old children, as well as in adults. Following a period of speech practice under conditions of altered auditory feedback, compensatory changes in speech production and perception were examined. Consistent with prior studies, the adults exhibited compensatory changes in both their speech motor output and their perceptual representations of speech sound categories. The children exhibited compensatory changes in the motor domain, with a change in speech output that was similar in magnitude to that of the adults, however the children showed no reliable compensatory effect on their perceptual representations. CONCLUSIONS: The results indicate that 9-11-year-old children, whose speech motor and perceptual abilities are still not fully developed, are nonetheless capable of auditory-feedback-based sensorimotor adaptation, supporting a role for such learning processes in speech motor development. Auditory feedback may play a more limited role, however, in the fine-tuning of children's perceptual representations of speech sound categories

The Role of Sensory Feedback in Developmental Stuttering: A Review

Developmental stuttering is a neurodevelopmental disorder that severely affects speech fluency. Multiple lines of evidence point to a role of sensory feedback in the disorder; this has led to a number of theories proposing different disruptions to the use of sensory feedback during speech motor control in people who stutter. The purpose of this review was to bring together evidence from studies using altered auditory feedback paradigms with people who stutter, in order to evaluate the predictions of these different theories. This review highlights converging evidence for particular patterns of differences in the responses of people who stutter to feedback perturbations. The implications for hypotheses on the nature of the disruption to sensorimotor control of speech in the disorder are discussed, with reference to neurocomputational models of speech control (predominantly, the DIVA model; Guenther et al., 2006; Tourville et al., 2008). While some consistent patterns are emerging from this evidence, it is clear that more work in this area is needed with developmental samples in particular, in order to tease apart differences related to symptom onset from those related to compensatory strategies that develop with experience of stuttering