Assessing Ecologically Valid Methods of Auditory Feedback Measurement in Individuals With Typical Speech

Purpose: Auditory feedback is thought to contribute to the online control of speech production. Yet, the standard method of estimating auditory feedback control (i.e., reflexive responses to auditory–motor perturbations), although sound, requires specialized instrumentation, meticulous calibration, unnatural tasks, and specific acoustic environments. The purpose of this study was to explore more ecologically valid features of speech production to determine their relationships with auditory feedback mechanisms. Method: Two previously proposed measures of within-utterance variability (centering and baseline variability) were compared with reflexive response magnitudes in 30 adults with typical speech. These three measures were estimated for both the laryngeal and articulatory subsystems of speech. Results: Regardless of the speech subsystem, neither centering nor baseline variability was shown to be related to reflexive response magnitudes. Likewise, no relationships were found between centering and baseline variability. Conclusions: Despite previous suggestions that centering and baseline variability may be related to auditory feedback mechanisms, this study did not support these assertions. However, the detection of such relationships may have required a larger degree of variability in responses, relative to that found in those with typical speech. Future research on these relationships is warranted in populations with more heterogeneous responses, such as children or clinical populations. Supplemental Material https://doi.org/10.23641/asha.17330546

Online Control of Voice Intensity in Late Bilinguals' First and Second Language Speech Production: Evidence From Unexpected and Brief Noise Masking

Purpose Speech production requires the combined efforts of feedforward control and feedback control subsystems. The primary purpose of this study is to explore whether the relative weighting of auditory feedback control is different between the first language (L1) and the second language (L2) production for late bilinguals. The authors also make an exploratory investigation into how bilinguals' speech fluency and speech perception relate to their auditory feedback control. Method Twenty Chinese–English bilinguals named Chinese or English bisyllabic words, while being exposed to 30- or 60-dB unexpected brief masking noise. Variables of language (L1 or L2) and noise condition (quiet, weak noise, or strong noise) were manipulated in the experiment. L1 and L2 speech fluency tests and an L2 perception test were also included to measure bilinguals' speech fluency and auditory acuity. Results Peak intensity analyses indicated that the intensity increases in the weak noise and strong noise conditions were larger in L2-English than L1-Chinese production. Intensity contour analysis showed that the intensity increases in both languages had an onset around 80–140 ms, a peak around 220–250 ms, and persisted till 400 ms post vocalization onset. Correlation analyses also revealed that poorer speech fluency or L2 auditory acuity was associated with larger Lombard effect. Conclusions For late bilinguals, the reliance on auditory feedback control is heavier in L2 than in L1 production. We empirically supported a relation between speech fluency and the relative weighting of auditory feedback control, and provided the first evidence for the production–perception link in L2 speech motor control.

Cortical network underlying speech production during delayed auditory feedback

Accurate and fluent production of speech strongly depends on hearing oneself which allows for the detection and correction of vocalization errors in real-time. When auditory feedback is disrupted with a time delay (e.g. echo on a conference call), it causes slowed and stutter-like speech in humans. Impaired speech motor control during delayed auditory feedback is implicated in various neurological disorders ranging from stuttering to aphasia, however the underlying neural mechanisms are poorly understood. Here, we investigated auditory feedback control in human speech by obtaining electrocorticographic recordings from neurosurgical subjects performing a delayed auditory feedback (DAF) task. We observed a significant increase in neural activity in auditory sites that scaled with the duration of feedback delay and correlated with response suppression during normal speech, providing direct evidence for a shared mechanism between sensitivity to altered feedback and speech-induced auditory suppression in humans. Furthermore, we find that when subjects robustly slowed down their speech rate to compensate for the delay, the dorsal division of the precentral gyrus was preferentially recruited to support articulation during an early time frame. This recruitment was accompanied by response enhancement across a large speech network commencing in temporal cortex and then engaging frontal and parietal sites. Our results highlight the critical components of the human speech network that support auditory feedback control of speech production and the temporal evolution of their recruitment.

The neural circuitry underlying the “rhythm effect” in stuttering

PurposeStuttering is characterized by intermittent speech disfluencies which are dramatically reduced when speakers synchronize their speech with a steady beat. The goal of this study was to characterize the neural underpinnings of this phenomenon using functional magnetic resonance imaging.MethodData were collected from 17 adults who stutter and 17 adults who do not stutter while they read sentences aloud either in a normal, self-paced fashion or paced by the beat of a series of isochronous tones (“rhythmic”). Task activation and task-based functional connectivity analyses were carried out to compare neural responses between speaking conditions and groups.ResultsAdults who stutter produced fewer disfluent trials in the rhythmic condition than in the normal condition. While adults who do not stutter had greater activation in the rhythmic condition compared to the normal condition in regions associated with speech planning, auditory feedback control, and timing perception, adults who stutter did not have any significant changes. However, adults who stutter demonstrated increased functional connectivity between bilateral inferior cerebellum and bilateral orbitofrontal cortex as well as increased connectivity among cerebellar regions during rhythmic speech as compared to normal speech.ConclusionModulation of connectivity in the cerebellum and prefrontal cortex during rhythmic speech suggests that this fluency-inducing technique activates a compensatory timing system in the cerebellum and potentially modulates top-down motor control and attentional systems. These findings corroborate previous work associating the cerebellum with fluency in adults who stutter and indicate that the cerebellum may be targeted to enhance future therapeutic interventions.

Contributions of Auditory and Somatosensory Feedback to Vocal Motor Control

Purpose To better define the contributions of somatosensory and auditory feedback in vocal motor control, a laryngeal perturbation experiment was conducted with and without masking of auditory feedback. Method Eighteen native speakers of English produced a sustained vowel while their larynx was physically and externally displaced on a subset of trials. For the condition with auditory masking, speech-shaped noise was played via earphones at 90 dB SPL. Responses to the laryngeal perturbation were compared to responses by the same participants to an auditory perturbation experiment that involved a 100-cent downward shift in fundamental frequency ( f o ). Responses were also examined in relation to a measure of auditory acuity. Results Compensatory responses to the laryngeal perturbation were observed with and without auditory masking. The level of compensation was greatest in the laryngeal perturbation condition without auditory masking, followed by the condition with auditory masking; the level of compensation was smallest in the auditory perturbation experiment. No relationship was found between the degree of compensation to auditory versus laryngeal perturbations, and the variation in responses in both perturbation experiments was not related to auditory acuity. Conclusions The findings indicate that somatosensory and auditory feedback control mechanisms work together to compensate for laryngeal perturbations, resulting in the greatest degree of compensation when both sources of feedback are available. In contrast, these two control mechanisms work in competition in response to auditory perturbations, resulting in an overall smaller degree of compensation. Supplemental Material https://doi.org/10.23641/asha.12559628

Auditory Feedback Control Mechanisms Do Not Contribute to Cortical Hyperactivity Within the Voice Production Network in Adductor Spasmodic Dysphonia

Purpose Adductor spasmodic dysphonia (ADSD), the most common form of spasmodic dysphonia, is a debilitating voice disorder characterized by hyperactivity and muscle spasms in the vocal folds during speech. Prior neuroimaging studies have noted excessive brain activity during speech in participants with ADSD compared to controls. Speech involves an auditory feedback control mechanism that generates motor commands aimed at eliminating disparities between desired and actual auditory signals. Thus, excessive neural activity in ADSD during speech may reflect, at least in part, increased engagement of the auditory feedback control mechanism as it attempts to correct vocal production errors detected through audition. Method To test this possibility, functional magnetic resonance imaging was used to identify differences between participants with ADSD ( n = 12) and age-matched controls ( n = 12) in (a) brain activity when producing speech under different auditory feedback conditions and (b) resting-state functional connectivity within the cortical network responsible for vocalization. Results As seen in prior studies, the ADSD group had significantly higher activity than the control group during speech with normal auditory feedback (compared to a silent baseline task) in three left-hemisphere cortical regions: ventral Rolandic (sensorimotor) cortex, anterior planum temporale, and posterior superior temporal gyrus/planum temporale. Importantly, this same pattern of hyperactivity was also found when auditory feedback control of speech was eliminated through masking noise. Furthermore, the ADSD group had significantly higher resting-state functional connectivity between sensorimotor and auditory cortical regions within the left hemisphere as well as between the left and right hemispheres. Conclusions Together, our results indicate that hyperactivation in the cortical speech network of individuals with ADSD does not result from hyperactive auditory feedback control mechanisms and rather is likely related to impairments in somatosensory feedback control and/or feedforward control mechanisms.