ObjectiveThis study examined adaptive responses to auditory perturbation of fundamental frequency (f o ) in speakers with Parkinson's disease (PD) and control speakers. MethodSixteen speakers with PD and nineteen control speakers produced sustained vowels while they received perturbed auditory feedback (i.e., f o shifted upward or downward). Speakers' pitch acuity was quantified using a just-noticeable-difference (JND) paradigm. Twelve listeners provided estimates of the speech intelligibility for speakers with PD. ResultsFifteen responses from each speaker group for each shift direction were included in analyses. While control speakers generally showed consistent adaptive responses opposing the perturbation, speakers with PD showed no compensation on average, with individual PD speakers showing highly variable responses. In the PD group, the degree of compensation was not significantly correlated with age, disease progression, pitch acuity, or intelligibility. ConclusionsThese findings indicate reduced adaptation to sustained f o perturbation and higher variability in PD compared to control participants. No significant differences were seen in pitch acuity between groups, suggesting that the f o adaptation deficit in PD is not the result of purely perceptual mechanisms. SignificanceThese results suggest there is an impairment in vocal motor control in PD. Building on these results, contributions can be made to developing targeted voice treatments for PD.PLOS ONE | https://doi.org/10.1371/journal.pone

Purpose: The vocal auditory-motor control of individuals with hyperfunctional voice disorders was examined using a sensorimotor adaptation paradigm. Method: Nine individuals with hyperfunctional voice disorders and 9 individuals with typical voices produced sustained vowels over 160 trials in 2 separate conditions: (a) while experiencing gradual upward perturbations in the fundamental frequency (f o ) of their auditory feedback (shift-up) and (b) under no auditory perturbation (control). The shift-up condition consisted of 4 ordered (fixed) phases: baseline (no perturbation), ramp (gradual increases in heard f o ), hold (a consistently higher heard f o ), and after-effect (no perturbation). Adaptive responses were defined as the difference in produced f o during control and shift-up conditions.Results: Adaptive responses were significantly different between groups. Individuals with typical voices generally showed compensatory adaptive responses, with decreased f o during the ramp and hold phases. Conversely, many individuals with hyperfunctional voice disorders instead displayed the opposite effect by following the direction of the perturbation. When f o was experimentally increased, speakers further increased their f o . Conclusion: Results indicate that some individuals diagnosed with hyperfunctional voice disorders have disrupted auditory-motor control, suggesting atypical neurological function. These findings may eventually allow for the development of new interventions for hyperfunctional voice disorders.

Purpose The purpose of this study was to explore the relationship between feedback and feedforward control of articulation and voice by measuring reflexive and adaptive responses to first formant ( F 1 ) and fundamental frequency ( f o ) perturbations. In addition, perception of F 1 and f o perturbation was estimated using passive (listening) and active (speaking) just noticeable difference paradigms to assess the relation of auditory acuity to reflexive and adaptive responses. Method Twenty healthy women produced single words and sustained vowels while the F 1 or f o of their auditory feedback was suddenly and unpredictably perturbed to assess reflexive responses or gradually and predictably perturbed to assess adaptive responses. Results Typical speakers' reflexive responses to sudden perturbation of F 1 were related to their adaptive responses to gradual perturbation of F 1 . Specifically, speakers with larger reflexive responses to sudden perturbation of F 1 had larger adaptive responses to gradual perturbation of F 1 . Furthermore, their reflexive responses to sudden perturbation of F 1 were associated with their passive auditory acuity to F 1 such that speakers with better auditory acuity to F 1 produced larger reflexive responses to sudden perturbations of F 1 . Typical speakers' adaptive responses to gradual perturbation of F 1 were not associated with their auditory acuity to F 1 . Speakers' reflexive and adaptive responses to perturbation of f o were not related, nor were their responses related to either measure of auditory acuity to f o . Conclusion These findings indicate that there may be disparate feedback and feedforward control mechanisms for articulatory and vocal error correction based on auditory feedback.

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.