Deficit or Difference? Effects of Altered Auditory Feedback on Speech Fluency and Kinematic Variability in Adults Who Stutter

Purpose The purpose of this study was to test whether adults who stutter (AWS) display a different range of sensitivity to delayed auditory feedback (DAF). Two experiments were conducted to assess the fluency of AWS under long-latency DAF and to test the effect of short-latency DAF on speech kinematic variability in AWS. Method In Experiment 1, 15 AWS performed a conversational speaking task under nonaltered auditory feedback and 250-ms DAF. The rates of stuttering-like disfluencies, other disfluencies, and speech errors and articulation rate were compared. In Experiment 2, 13 AWS and 15 adults who do not stutter (AWNS) read three utterances under four auditory feedback conditions: nonaltered auditory feedback, amplified auditory feedback, 25-ms DAF, and 50-ms DAF. Across-utterance kinematic variability (spatiotemporal index) and within-utterance variability (percent determinism and stability) were compared between groups. Results In Experiment 1, under 250-ms DAF, the rate of stuttering-like disfluencies and speech errors increased significantly, while articulation rate decreased significantly in AWS. In Experiment 2, AWS exhibited higher kinematic variability than AWNS across the feedback conditions. Under 25-ms DAF, the spatiotemporal index of AWS decreased significantly compared to the other feedback conditions. AWS showed lower overall percent determinism than AWNS, but their percent determinism increased under 50-ms DAF to approximate that of AWNS. Conclusions Auditory feedback manipulations can alter speech fluency and kinematic variability in AWS. Longer latency auditory feedback delays induce speech disruptions, while subtle auditory feedback manipulations potentially benefit speech motor control. Both AWS and AWNS are susceptible to auditory feedback during speech production, but AWS appear to exhibit a distinct continuum of sensitivity.

Stutter and phenomena: The phenomenology and deconstruction of delayed auditory feedback

Jacques Derrida’s early critique of Husserlian phenomenology discusses the production of the ‘phenomenological voice’ as the consummate model of human consciousness. Challenging Husserl’s conviction that consciousness is produced from the self-enclosed act of ‘hearing-oneself-speak’, Derrida points to vocality as the complex site of the self’s relationship to presence and exteriority. The internal division between hearing and speaking, he argues, introduces difference into the generation of conscious life. The use of delayed auditory feedback (DAF) as a prosthetic for stuttering provides an opportunity to engage Derrida’s insights on the connection between consciousness and voice with an ear to the speech of people who stutter. DAF, which may reduce or increase dysfluency depending on the speech of the user, introduces a series of delays, alterations and supplements to speech that underwrite the heterogeneous experience of conscious life. What can the philosophy of deconstruction add to conversations about the function of DAF, and what can theory about and experiences with DAF teach us about the self’s presence to itself and the role of alterity in shaping speech? What does stuttering teach us about the necessity of dysfluency for all speech? This article examines the relation between the voice and the phenomenological voice, and between stuttering and prosthetics. Concluding with an analysis of Richard Serra’s experimental recording, Boomerang (1974), it argues that voice is always already prostheticized with alterity, and that in hearing-oneself-speak we exist with voice in an expansive and unfinished conversation with our own mystery.

Investigation of the effect of Delayed Auditory Feedback and transcranial Direct Current Stimulation (DAF-tDCS) treatment for the enhancement of speech fluency in adults who stutter: a Randomized Controlled Trial

Background: With a population prevalence of one percent, stuttering is among the main speech pathology-related topics of research. Adults who stutter may benefit from transcranial direct current stimulation (tDCS) as an adjunctive intervention for enhancing speech fluency. In this study, Delayed Auditory Feedback (DAF) was combined with tDCS applied over the superior temporal gyrus. It was anticipated that the combined intervention cause improvements in speech fluency.Methods: A randomized, double-blind, sham-controlled clinical trial was conducted to investigate the effectiveness of intervention in enhancing speech fluency. Fifty participants were randomly allocated to the intervention or control group. In the intervention group, participants received DAF combined with anodal tDCS, while the control group was exposed to sham tDCS simultaneously with DAF. Each subject participated in six intervention sessions. Speech fluency was assessed as the baseline, before intervention as well as immediately, one week and six weeks after intervention. Results: In the intervention group, the percentage of stuttered syllables was significantly reduced immediately, one week and six weeks after the intervention, as compared with the control group. The scores of the Stuttering Severity Instrument, also showed a significant reduction in the intervention group compared with the control group. No significant difference was found in the Overall Assessment of the Speaker’s Experience of Stuttering questionnaire scores between the two groups after intervention. Conclusion: The results of this study propose anodal tDCS as an adjunctive method to increase speech fluency in stuttering for a prolonged time course after intervention, when combined with fluency therapy.Trial registration: This trial was registered in ClinicalTrial.gov before recruiting the subjects. The registration number is NCT03990168 and the date of registration is June 18, 2019. https://clinicaltrials.gov/ct2/show/NCT03990168

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.

Investigation of the effect of Delayed Auditory Feedback and transcranial Direct Current Stimulation (DAF-tDCS) treatment for the enhancement of speech fluency in adults who stutter: a Randomized Controlled Trial

Background: With a population prevalence of one percent, stuttering is among the main speech pathology-related topics of research. Adults who stutter may benefit from transcranial direct current stimulation (tDCS) as an adjunctive intervention for enhancing speech fluency. In this study, Delayed Auditory Feedback (DAF) was combined with tDCS applied over the superior temporal gyrus. It was anticipated that intervention caused improvements of speech fluency become more stable.Methods: A randomized, double-blind, sham-controlled clinical trial was conducted to investigate the effectiveness of intervention in enhancing speech fluency. Fifty participants were randomly allocated the intervention or control group. In the intervention group, participants received DAF combined with anodal tDCS, while the control group was exposed to sham tDCS simultaneously with DAF. Each subject participated in six intervention sessions. Speech fluency was assessed before intervention as baseline, as well as immediately, one week and six weeks after intervention.Results: In the intervention group, the percentage of stuttered syllables was significantly reduced immediately, one week and six weeks after the intervention, as compared with the control group. The scores of the Stuttering Severity Instrument, also showed a significant reduction in the intervention group compared with the control group. No significant difference was found in the Overall Assessment of the Speaker’s Experience of Stuttering questionnaire scores between the two patient two groups after intervention.Conclusion: The results of this study propose anodal tDCS as an adjunctive method to increase speech fluency in stuttering for a prolonged time course after intervention, when combined with fluency therapy.Trial registration: This trial was registered in ClinicalTrial.gov before recruiting the subjects. The registration number is NCT03990168 and the date of registration is June 18, 2019. https://clinicaltrials.gov/ct2/show/NCT03990168

Speed, Accuracy, and Efficiency of Judgements of Coincidence between Speech Acts and Auditory Perception during a Delayed Auditory Feedback Paradigm: A Behavioral Study in Patients with Schizophrenia

The inability to differentiate between one’s actions and their consequences from sensory inputs originating from an alien source might cause classical first-rank symptoms in schizophrenia, such as audio-verbal hallucinations (AVH). We aimed to determine whether patients with or without AVH perform differently in a task challenging the audio-verbal self-monitoring system compared to controls. Controls (n = 21) and schizophrenia patients with (AH, n = 11) and without AVH (NH, n = 9) participated. Subjects had to discern whether they heard a sound they had just uttered with or without delay. Reaction time, accuracy as well as sensitivity and response bias were compared between groups. There were no group effects in reaction time. Controls were significantly more accurate in the detection of delays compared to AH and to NH. However, the most salient observation was that these deficits were not uniformly present, but were selectively elicited by the delay, reducing patients’ response accuracy to chance level. The analysis of the data based on signal detection theory revealed a significant drop in sensitivity in both patient groups compared to the controls, and a response bias: Particularly the patients with AVH seemed to be biased not to consider a delay, rather than falsely signaling a delay. Such a deficit may blur the distinction between external events and self-initiated actions, thus eventually interfering with the patients’ sense of agency.