Papers Related to Lab Projects
Comparison of voice F0 responses to pitch-shift onset and offset conditions
Larson, C.R., Burnett, T.A., Bauer, J. J., Kiran, S., & Hain, T.C. (In Press). Comparison of voice F0 responses to pitch-shift onset and offset conditions. Journal of the Acoustical Society of America.
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In order to maintain a steady voice fundamental frequency (F0), 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 F0 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.
Effect of Duration of Pitch-Shifted Feedback on Vocal Responses in Parkinson's Disease Patients and Normal Controls
Kiran, S., & Larson, C.R. (2001). Effect of Duration of Pitch-Shifted Feedback on Vocal Responses in Parkinson's Disease Patients and Normal Controls. Journal of Speech Language and Hearing Research, 44, 975-987.
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Study of the pitch-shift reflex is useful for the investigation of how auditory feedback is used in the control of voice fundamental frequency. The present study was an attempt to learn if the basal ganglia are involved in central mechanisms of the pitch-shift reflex by comparing measures of the reflex in a group of Parkinson's Disease patients with control participants. The effect of varying duration of the pitch-shift stimulus (PSS) on the voice fundamental frequency (F0) response in 10 Parkinson's disease (PD) patients and 10 age-matched normal controls was investigated. Participants were instructed to vocalize into a microphone while their voice was fed back to them over headphones. This feedback of the vocal signal was shifted in pitch either up or down, with the duration of this shift systematically manipulated at 100 ms, 500 ms and 1000 ms. Although the participants were on medication, making interpretation of the results problematic with regard to basal ganglia function, it was reasoned that positive effects could nevertheless suggest basal ganglia involvement in this reflex and motivate further research. Results indicated that both groups responded to increased stimulus duration of the pitch-shift stimulus with increases in reflex peak time, magnitude and end times. However, PD patients had significantly longer peak times and end times than controls for stimulus durations of 100 ms. These results suggest that basal ganglia dysfunction may affect mechanisms relating to the execution and termination of the pitch-shift reflex for brief stimulus durations. The results also support hypotheses of impaired sensory integration of auditory feedback in PD patients.
Effects of delayed auditory feedback (DAF) on the pitch-shift reflex
Hain, T.C., Burnett, T.A., Larson, C.R., & Kiran, S. (2001). Effects of delayed auditory feedback (DAF) on the pitch-shift reflex. Journal of the Acoustical Society of America, 109, 2146-2152.
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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., 1998; Hain et al., 2000; Larson et al., 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 F0.
Instructing Subjects to Make a Voluntary Response Reveals the Presence of Two Components to the Audio - Vocal Reflex
Hain, T.C., Burnett, T.A., Kiran, S., Larson, C.R., Singh, S., & Kenney, M.K. (2000). Instructing Subjects to Make a Voluntary Response Reveals the Presence of Two Components to the Audio - Vocal Reflex. Experimental Brain Research, 130, 133-141.
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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 that it could 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 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.
Effects of pitch-shift velocity on voice F0 responses
Larson, C.R., Burnett, T.A., Kiran, S., Kenney, M.K., & Hain, T.C. (2000). Effects of pitch-shift velocity on voice F0 responses. Journal of the Acoustical Society of America, 101 (1), 559-564.
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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 co-varied 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
Voice F0 Responses to Manipulations in Pitch Feedback
Burnett, T.A., Freedland, M.B., Larson, C.R., & Hain, T.C. (1998). Voice F0 Responses to Manipulations in Pitch Feedback. Journal of the Acoustical Society of America, 103, 3153-3161.
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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.
