Auditory feedback control in adults who stutter during metronome-paced speech II. Formant Perturbation

Abstract

Purpose: Prior work has shown that Adults who stutter (AWS) have reduced and delayed responses to auditory feedback perturbations. This study aimed to determine whether external timing cues, which increase fluency, resolve auditory feedback processing disruptions.

Methods: Fifteen AWS and sixteen adults who do not stutter (ANS) read aloud a multisyllabic sentence either with natural stress and timing or with each syllable paced at the rate of a metronome. On random trials, an auditory feedback formant perturbation was applied, and formant responses were compared between groups and pacing conditions.

Results: During normally paced speech, ANS showed a significant compensatory response to the perturbation by the end of the perturbed vowel, while AWS did not. In the metronome-paced condition, which significantly reduced the disfluency rate, the opposite was true: AWS showed a significant response by the end of the vowel, while ANS did not.

Conclusion: These findings indicate a potential link between the reduction in stuttering found during metronome-paced speech and changes in auditory motor integration in AWS.

Keywords: Auditory feedback; Metronome; Speech timing control; Stuttering.

Figure 1.

A schematic diagram showing the setup for the experiment. Following the presentation of an orthographic stimulus sentence and a condition cue (“Normal” or “Rhythm”), participants read the sentence according to the cue. Participants’ speech signals were recorded and fed to an experimental computer running Audapter. On perturbed trials, detection of the onset of /ε/ in “steady” was used to initiate the pre-programmed auditory perturbation which was fed back to the participant via insert earphones. Both the perturbed and unperturbed signals were recorded for further analysis.

Figure 2:

Example spectrograms of “The steady bat” during a formant perturbation trial generated from the recorded microphone signal (top) and headphone signal (bottom). The first and second formant traces during the word “steady” are displayed. In the headphone signal spectrogram, the original formant traces are displayed in black and the shifted formant traces are overlaid in blue. Note that only the first formant is perturbed. Phoneme boundaries and international phonetic alphabet symbols are indicated above the microphone signals. F1 = first formant, F2 = second formant, Hz = hertz.

Figure 3.

Disfluency rate in the normal and metronome-paced conditions for AWS. Circles represent individual participants.

Figure 4.

Time-normalized formant responses to the F1 perturbation during the /ε/ in “steady” in the normal (A) and metronome-paced (B) conditions. Solid curves indicate the average difference in F1 frequency between the perturbed and non-perturbed conditions for ANS (blue) and AWS (orange). Dashed lines indicate mean formant change response +/− standard error of the mean. The blue bars indicate intervals of significant responses in ANS (p < 0.05, uncorrected). The orange bars represent intervals of significant responses in AWS (p < 0.05, uncorrected). The magenta bars indicate intervals of significant differences between ANS and AWS (p < 0.05, uncorrected). Duration of the non-normalized /ε/ response curves (averaged between perturbed and non-perturbed trials and across subjects) for each group and speaking condition are included to the right of the response curves for reference.