Feedback and Feedforward Auditory-Motor Processes for Voice and Articulation in Parkinson's Disease.

PURPOSE: Unexpected and sustained manipulations of auditory feedback during speech production result in "reflexive" and "adaptive" responses, which can shed light on feedback and feedforward auditory-motor control processes, respectively. Persons with Parkinson's disease (PwPD) have shown aberrant reflexive and adaptive responses, but responses appear to differ for control of vocal and articulatory features. However, these responses have not been examined for both voice and articulation in the same speakers and with respect to auditory acuity and functional speech outcomes (speech intelligibility and naturalness). METHOD: Here, 28 PwPD on their typical dopaminergic medication schedule and 28 age-, sex-, and hearing-matched controls completed tasks yielding reflexive and adaptive responses as well as auditory acuity for both vocal and articulatory features. RESULTS: No group differences were found for any measures of auditory-motor control, conflicting with prior findings in PwPD while off medication. Auditory-motor measures were also compared with listener ratings of speech function: first formant frequency acuity was related to speech intelligibility, whereas adaptive responses to vocal fundamental frequency manipulations were related to speech naturalness. CONCLUSIONS: These results support that auditory-motor processes for both voice and articulatory features are intact for PwPD receiving medication. This work is also the first to suggest associations between measures of auditory-motor control and speech intelligibility and naturalness.

Auditory-Motor Perturbations of Voice Fundamental Frequency: Feedback Delay and Amplification.

Purpose Gradual and sudden perturbations of vocal fundamental frequency (f o), also known as adaptive and reflexive f o perturbations, are techniques to study the influence of auditory feedback on voice f o control mechanisms. Previous vocal f o perturbations have incorporated varied setup-specific feedback delays and amplifications. Here, we investigated the effects of feedback delays (10-100 ms) and amplifications on both adaptive and reflexive f o perturbation paradigms, encapsulating the variability in equipment-specific delays (3-45 ms) and amplifications utilized in previous experiments. Method Responses to adaptive and reflexive f o perturbations were recorded in 24 typical speakers for four delay conditions (10, 40, 70, and 100 ms) or three amplification conditions (-10, +5, and +10 dB relative to microphone) in a counterbalanced order. Repeated-measures analyses of variance were carried out on the magnitude of f o responses to determine the effect of feedback condition. Results There was a statistically significant effect of the level of auditory feedback amplification on the response magnitude during adaptive f o perturbations, driven by the difference between +10- and -10-dB amplification conditions (hold phase difference: M = 38.3 cents, SD = 51.2 cents; after-effect phase: M = 66.1 cents, SD = 84.6 cents). No other statistically significant effects of condition were found for either paradigm. Conclusions Experimental equipment delays below 100 ms in behavioral paradigms do not affect the results of f o perturbation paradigms. As there is no statistically significant difference between the response magnitudes elicited by +5- and +10-dB auditory amplification conditions, this study is a confirmation that an auditory feedback amplification of +5 dB relative to microphone is sufficient to elicit robust compensatory responses for f o perturbation paradigms.

Visual Analog Scale Ratings and Orthographic Transcription Measures of Sentence Intelligibility in Parkinson's Disease With Variable Listener Exposure.

Purpose While orthographic transcription (OT) is the gold standard for measures of intelligibility, it is relatively inaccessible to clinicians. This study investigates the relationship between visual analog scale (VAS) ratings and OT measures of intelligibility for speakers with Parkinson's disease (PD), with the eventual goal of developing more clinically feasible assessments of intelligibility. Method Twenty speakers with PD and 5 controls read 11 sentences. First, 33 listeners completed an OT task using 1 sentence from each speaker. An additional 33 listeners rated the intelligibility of 1 sentence from each speaker using a VAS, reflecting a minimized exposure VAS (MEV) task. Lastly, 14 additional listeners each rated the intelligibility of all 11 sentences produced by all speakers using a VAS, reflecting an extended exposure VAS (EEV) task. Smaller listener groups were simulated from each VAS task for comparison to scores from the OT task. Results There was a strong relationship between OT and both MEV and EEV. This relationship remained strong (R 2 ≥ .82) even when only 1 listener in MEV and 2 listeners in EEV were simulated per sentence. Conclusions VAS ratings may be a suitable alternative to OT measures of sentence intelligibility for PD using listeners with both minimal and extended exposure to the stimuli.

The Relationship Between Physiological Mechanisms and the Self-Perception of Vocal Effort.

Purpose This study aimed to examine the relationship between a large set of hypothesized physiological measures of vocal effort and self-ratings of vocal effort. Method Twenty-six healthy adults modulated speech rate and vocal effort during repetitions of the utterance /ifi/, followed by self-perceptual ratings of vocal effort on a visual analog scale. Physiological measures included (a) intrinsic laryngeal tension via kinematic stiffness ratios determined from high-speed laryngoscopy, (b) extrinsic suprahyoid and infrahyoid laryngeal tension via normalized percent activations and durations derived from surface electromyography, (c) supraglottal compression via expert visual-perceptual ratings, and (d) subglottal pressure via magnitude of neck surface vibrations from an accelerometer signal. Results Individual statistical models revealed that all of the physiological predictors, except for kinematic stiffness ratios, were significantly predictive of self-ratings of vocal effort. However, a combined regression model analysis yielded only 3 significant predictors: subglottal pressure, mediolateral supraglottal compression, and the normalized percent activation of the suprahyoid muscles (adjusted R 2 = .60). Conclusions Vocal effort manifests as increases in specific laryngeal physiological measures. Further work is needed to examine these measures in combination with other contributing factors, as well as in speakers with dysphonia.