Recent studies have shown that when phonating subjects hear their voice pitch feedback shift upward or downward, they respond with a change in voice fundamental frequency (F0) output. Three experiments were performed to improve our understanding of this response and to explore the effects of different stimulus variables on voice F0 responses to pitch-shift stimuli. In experiment 1, it was found that neither the absolute level of feedback intensity nor the presence of pink masking noise significantly affect magnitude or latency of the voice F0 response. In experiment 2, changes in stimulus magnitude led to no systematic differences in response magnitudes or latencies. However, as stimulus magnitude was increased from 25 to 300 cents, the proportion of responses that changed in the direction opposite that of the stimulus ("opposing" response) decreased. A corresponding increase was observed in the proportion of same direction responses ("following" response). In experiment 3, increases in pitch-shift stimulus durations from 20 to 100 ms led to no differences in the F0 response. Durations between 100 and 500 ms led to longer duration voice F0 responses with greater response magnitude, and suggested the existence of a second F0 response with a longer latency than the first.

Previous findings have shown that subjects respond to an alteration, or shift, of auditory feedback pitch with a change in voice fundamental frequency (F0). When pitch shifts exceeding 500 ms in duration were presented, subjects' averaged responses appeared to consist of both an early and a late component. The latency of the second response was long enough to be produced voluntarily. To test the hypothesis that there are two responses to pitch-shift stimuli and to clarify the role of intention, subjects were instructed to change their voice F0 in the opposite direction of the pitch-shift stimulus, in the same direction, or not to respond at all. In a second group, subjects were tested under the above conditions as well as under instructions to raise voice F0 or to lower F0 as rapidly as possible upon hearing a pitch shift. Results showed that, when given instructions to produce a voluntary response, subjects made both an early vocal response (VR1) and a later vocal response (VR2). The second response, VR2, was almost always made in the instructed direction, whereas VR1 was often made incorrectly. The latency of VR1 was reduced under instructions to respond to feedback pitch shifts by changing voice F0 in the opposite direction, compared with that when told to ignore the pitch shifts. Latency and amplitude measures of VR2 differed under the various experimental conditions. These results demonstrate that there are two responses to pitch-shift stimuli. The first is relatively automatic but may be modulated by instructions to the participant. The second response is probably a voluntary one.

No abstract

Previous studies have shown that voice fundamental frequency (F0) is modified by changes in the pitch of vocal feedback and have demonstrated that the audio-vocal control system has both open- and closed-loop control properties. However, the extent to which this system operates in closed-loop fashion may have been underestimated in previous work. Because the step-type stimuli used were very rapid, and people are physically unable to change their voice F0 as rapidly as the stimuli, feedback responses might have been reduced or suppressed. In the present study, pitch-shift stimuli, consisting of a disparity between voice F0 and feedback pitch of varying ramp onset velocities, were presented to subjects vocalizing a steady /ah/ sound to examine the effect of stimulus onset on voice F0 responses. Results showed that response velocity covaried with stimulus velocity. Response latency and time of the peak response decreased with increases in stimulus velocity, while response magnitude decreased. A simple feedback model reproduced most features of these responses. These results strongly support previous suggestions that the audio-vocal system monitors auditory feedback and, through closed-loop negative feedback, adjusts voice F0 so as to cancel low-level fluctuations in F0.

In order to maintain a steady voice fundamental frequency (F 0 ), it is assumed that people compare their auditory feedback pitch with an internal (memory) or external (acoustic) referent. In the present study we examined whether the internal referent is fixed or variable by comparing voice F 0 responses to incorrect auditory feedback in two timing conditions. In one condition, the incorrect pitch was introduced during vocalization (ON condition). In the second, the incorrect auditory feedback pitch was presented before vocal onset and then removed during vocalization (OFF condition). These conditions were examined with pitch-shift stimuli of ±25, 100, and 200 cents. There were no differences in response latency or magnitude between the two timing conditions, indicating that for a sustained-pitch vocalization task, the internal referent is not fixed. Several alternative types of referencing are discussed, which include use of a pitch relative to that which existed at the onset of vocalization (a sample and hold strategy) and pitch velocity referencing.