Theresa A. Burnett

Voice F0 responses to pitch-shifted auditory feedback: a preliminary study

Auditory feedback has been suggested to be important for voice fundamental frequency (F0) control. The present study featured a new technique for testing this hypothesis by which the pitch of a subjects voice was modulated, fed back over earphones, and the resultant change in the emitted voice F0 was measured. The responses of 67 normal, healthy young adults were recorded as they attempted to ignore intermittent upward or downward shifts in pitch feedback while they sustained steady vowel sounds (/a/) or sang musical scales. Ninety-six percent of subjects increased their F0 when the feedback pitch was decreased, and 78% of subjects decreased their F0 when the pitch feedback was increased. Latencies of responses ranged from 104 to 223 ms. Results indicate people normally rely on pitch feedback to control voice F0.

Effects of pitch-shift velocity on voice F0 responses

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.

The Effect of Neuromuscular Stimulation of the Genioglossus on the Hypopharyngeal Airway

Objectives To determine the effects of neuromuscular stimulation (NS) of the genioglossus muscle on hypopharyngeal airway size.

Comparison of voice F0 responses to pitch-shift onset and offset conditions

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 h...

Voice F0 responses to actual versus consciously perceived auditory feedback pitch shifts

The purpose of this study was to determine the effect of pitch shift discrimination ability on production of voice F0 responses to auditory feedback pitch shifts. Subjects repeatedly vocalized /u/ into a microphone while listening to their voice fed back over headphones. During each trial, auditory feedback pitch was experimentally shifted upward or downward (randomly determined) by 50 cents for 100 ms. Subjects subsequently pressed a button labeled up or down to indicate their perceived direction of voice feedback pitch shift. Voice output was recorded, F0 extracted, smoothed, time aligned to the onset of the pitch shift, and averaged. Button response accuracy was found to be at chance expectancy among the majority of subjects. Nevertheless, all subjects responded vocally to the pitch shifts by changing voice F0 in the opposite direction, indicating that the direction of the shift was indeed processed by the auditory system. These results are consistent with the existence of preattentive mechanisms of au...

Re‐examining the effects of perturbation magnitude, direction, and duration on the pitch‐shift reflex.

Comparing average voice fundamental frequency (F0) responses to pitch‐shifted auditory feedback has revealed effects of some stimulus parameters, but not of others. We hypothesize that some stimulus effects on pitch‐shift reflex characteristics are spurious, the result of differences in the incidence of the pitch‐shift reflex rather than its inherent characteristics. Using a template correlation analysis technique that allows the pitch‐shift reflex to be identified in individual trials, the effects of stimulus magnitude, direction, and duration were re‐examined. We presented 30 healthy adults with auditory feedback pitch shifts during sustained phonation of the vowel /u/. Pitch shifts were all combinations of magnitude (50, 300, and 600 cents), Direction (up and down) and duration (100 and 500 ms) for a total of 12 conditions. Results indicate significant effects of pitch perturbation magnitude and direction on the incidence of the pitch‐shift reflex. Implications for our understanding of voice F0 respons...

Age effects of pitch‐shifted auditory feedback on reflexive and volitional voice F0 control

Research on voice fundamental frequency (F0) control suggests that when making a voluntary vocal response to a pitch change in voice auditory feedback, the pitch‐shift reflex typically occurs before the volitional response is initiated. The current study examined the effects of aging on reflexive and volitional voice F0 responses to pitch‐shifted auditory feedback. Thirty participants (age range 19 to 78 years) repeatedly sustained an /u/ vocalization at a steady pitch and loudness while listening to their voice fed backed over headphones. Once per vocalization, feedback pitch was randomly shifted upward or downward for 100 milliseconds and 20 or 100 cents. In the Sustain condition, participants attempted to ignore the pitch change in auditory feedback voice. In the Follow condition, participants immediately changed their pitch in the same direction as the auditory pitch shift they heard. Preliminary results from thirteen participants indicate that there appears to be no effect of aging on the first F0 re...

Correlations between voice F0 responses and manual reaction times to auditory feedback pitch shifts

There appear to be two types of voice F0 responses to voice auditory feedback pitch manipulations: early, opposing responses, and later responses that vary across subject and task. The purpose of this study was to determine whether either type correlates with volitional motor abilities. Subjects vocalized /u/ into a microphone while listening to their voice fed back over headphones. Subjects also pressed a joystick button as rapidly as possible upon hearing any experimenter‐generated auditory feedback pitch shift. Pitch shift stimuli were 50 cents upward or downward (randomized), and 100‐ms duration. Voice was recorded, F0 extracted, smoothed, time aligned to the onset of the shift, averaged according to shift direction, and the onset of the first voice F0 response was measured. Average manual reaction time was calculated. Findings indicated no significant correlation between manual responses and early voice F0 response. However, later voice F0 responses and manual reaction times were positively correlate...

Effect of target source and dynamics on voice F0 stability in the presence of auditory feedback pitch perturbations

The quickness with which a motor system recovers from an unanticipated perturbation is an indication of its stability. This principle was examined with regard to the voice F0 control system and auditory feedback. Trained singers sang a steady note or an upward glissando, either from memory or by tracking a synthesized tone. At an unanticipated time during phonation, the singers’ auditory feedback pitch was ‘‘flattened’’ by 1 semitone for a period of 100 ms, creating an effect similar to that which would be heard during a production error. All singers produced voice F0 changes in response to the auditory perturbations, and many of these voice F0 changes were oscillatory in nature. The number of oscillations and the speed with which they were dampened were measured and compared across the different types of vocal productions (steady note versus glissando) and across the different target sources (pitch memory versus synthesized tone). Results indicate that voice pitch stability varies with the nature of the ...

Voice F0 responds to auditory feedback pitch shifts during both steady and dynamic vocal behaviors

When trying to hold steady voice fundamental frequency (F0), subjects vocally oppose experimentally introduced small upward or downward shifts in auditory feedback pitch. These voice F0 responses have a latency of 100–150 ms, and occur despite efforts by subjects to ignore the feedback pitch shifts. The consistent and involuntary nature of these responses provides evidence of closed‐loop fine control of voice F0. Studies of oculomotor and limb movement systems have revealed different control strategies for static versus dynamic behaviors. It is not clear whether the fine control voice F0 likewise differs. For this reason, a study was undertaken to determine if the voice F0 response to pitch‐shifted auditory feedback was affected by task dynamics. Specifically, a comparison was made between responses to pitch shifts introduced during voice F0 hold and ramp tasks. Results indicate a similar role of the voice F0 response across both vocal behaviors, namely, to facilitate production of an intended target, be ...