Effects of delayed auditory feedback (DAF) on the pitch-shift reflex.

Changes in voice pitch auditory feedback to vocalizing subjects elicit compensatory changes in voice fundamental frequency (F0). The neural mechanisms responsible for this behavior involve the auditory and vocal-motor systems, collectively known as the audio-vocal system. Previous work [Burnett et al., J. Acoust. Soc. Am. 103, 3153-3161 (1998); Hain et al., Exp. Brain Res. 130, 133-141 (2000); Larson et al., J. Acoust. Soc. Am. 107, 559-564 (2000)] indicated that this system operates using negative feedback to cancel out low-level errors in voice F0 output. By introducing delays in the auditory feedback pathway, we hoped to transiently "open" the feedback loop and learn which components of the response are most closely related to the timing of the auditory feedback signal. Subjects were presented with pitch-shift stimuli that were paired with a delay of 0, 50, 100, 200, 300, or 500 ms. Delayed auditory feedback did not affect voice F0 response latency or magnitude, but it delayed the timing of later parts of the response. As a further test of the audio-vocal control system, a second experiment was conducted in which delays of 100, 200, or 300 ms were combined with stimuli having onset velocities of 1000 or 330 cents/s. Results confirmed earlier reports that the system is sensitive to velocity of stimulus onset. A simple feedback model reproduced most features of both experiments. These results strongly support previous suggestions that the audio-vocal system monitors auditory feedback and, through closed-loop negative feedback incorporating a delay, adjusts voice F0 so as to cancel unintentional small magnitude fluctuations in F0.