The role of auditory feedback in sustaining vocal vibrato.
Vocal vibrato and tremor are characterized by oscillations in voice fundamental frequency (F0). These oscillations may be sustained by a control loop within the auditory system. One component of the control loop is the pitch-shift reflex (PSR). The PSR is a closed loop negative feedback reflex that is triggered in response to discrepancies between intended and perceived pitch with a latency of approximately 100 ms. Consecutive compensatory reflexive responses lead to oscillations in pitch every approximately 200 ms, resulting in approximately 5-Hz modulation of F0. Pitch-shift reflexes were elicited experimentally in six subjects while they sustained /u/ vowels at a comfortable pitch and loudness. Auditory feedback was sinusoidally modulated at discrete integer frequencies (1 to 10 Hz) with +/- 25 cents amplitude. Modulated auditory feedback induced oscillations in voice F0 output of all subjects at rates consistent with vocal vibrato and tremor. Transfer functions revealed peak gains at 4 to 7 Hz in all subjects, with an average peak gain at 5 Hz. These gains occurred in the modulation frequency region where the voice output and auditory feedback signals were in phase. A control loop in the auditory system may sustain vocal vibrato and tremorlike oscillations in voice F0.
D000328:Adult; D003056:Cochlear Nerve / Q000502:physiology; D005246:Feedback / Q000502:physiology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007821:Laryngeal Muscles / Q000294:innervation; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D010897:Pitch Discrimination / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D013018:Sound Spectrography; D014833:Voice Quality / Q000502:physiology*