Auditory-Motor Control of Fundamental Frequency in Vocal Vibrato.

Purpose: The purpose of this study was to investigate how classically trained singers use their auditory feedback to control fundamental frequency (f) during production of vocal vibrato. Two main questions were addressed: (1) Do singers produce reflexive fresponses to sudden perturbation of the f of their auditory feedback during production of vibrato indicative of feedback control? (2) Do singers produce adaptive fresponses to repeated perturbation of the f of their auditory feedback during production of vibrato indicative of feedback and feedforward control? In addition, one methodological question was addressed to determine if adaptive f responses were more precisely assessed with or without an auditory cue for f during the repeated f perturbation paradigm.

Method: Ten classically trained singers produced sustained vowels with vibrato while the f and harmonics of their auditory feedback were suddenly perturbed by 100 cents to assess reflexive control or repeatedly perturbed by 100 cents to assess adaptive control. Half of the participants completed the repeated perturbation experiment with an auditory cue for f, and the other half completed the experiment without an auditory cue for f. Acoustical analyses measured changes in mean f in response to the auditory feedback perturbations.

Results: On average, participants produced compensatory responses to both sudden and repeated perturbation of the f of their auditory feedback. The magnitude of the responses to repeated perturbations was larger than the responses to sudden perturbations. Responses were also larger in the cued, repeated f perturbation experiment than in the uncued, repeated f perturbation experiment.

Conclusions: These findings indicate that classically-trained singers use both feedforward and feedback mechanisms to control their average f during production of vibrato. When compared to prior studies of singers producing a steady voice, the reflexive f responses were larger in the current study, which may indicate that the feedback control system is engaged more during production of vibrato.