Jay J. Bauer

Vocal responses to unanticipated perturbations in voice loudness feedback: An automatic mechanism for stabilizing voice amplitude

The present study tested whether subjects respond to unanticipated short perturbations in voice loudness feedback with compensatory responses in voice amplitude. The role of stimulus magnitude (+/- 1,3 vs 6 dB SPL), stimulus direction (up vs down), and the ongoing voice amplitude level (normal vs soft) were compared across compensations. Subjects responded to perturbations in voice loudness feedback with a compensatory change in voice amplitude 76% of the time. Mean latency of amplitude compensation was 157 ms. Mean response magnitudes were smallest for 1-dB stimulus perturbations (0.75 dB) and greatest for 6-dB conditions (0.98 dB). However, expressed as gain, responses for 1-dB perturbations were largest and almost approached 1.0. Response magnitudes were larger for the soft voice amplitude condition compared to the normal voice amplitude condition. A mathematical model of the audio-vocal system captured the main features of the compensations. Previous research has demonstrated that subjects can respond to an unanticipated perturbation in voice pitch feedback with an automatic compensatory response in voice fundamental frequency. Data from the present study suggest that voice loudness feedback can be used in a similar manner to monitor and stabilize voice amplitude around a desired loudness level.

Compensation for pitch-shifted auditory feedback during the production of Mandarin tone sequences

Recent research has found that while speaking, subjects react to perturbations in pitch of voice auditory feedback by changing their voice fundamental frequency (F0) to compensate for the perceived pitch-shift. The long response latencies (150-200 ms) suggest they may be too slow to assist in on-line control of the local pitch contour patterns associated with lexical tones on a syllable-to-syllable basis. In the present study, we introduced pitch-shifted auditory feedback to native speakers of Mandarin Chinese while they produced disyllabic sequences /ma ma/ with different tonal combinations at a natural speaking rate. Voice F0 response latencies (100-150 ms) to the pitch perturbations were shorter than syllable durations reported elsewhere. Response magnitudes increased from 50 cents during static tone to 85 cents during dynamic tone productions. Response latencies and peak times decreased in phrases involving a dynamic change in F0. The larger response magnitudes and shorter latency and peak times in tasks requiring accurate, dynamic control of F0, indicate this automatic system for regulation of voice F0 may be task-dependent. These findings suggest that auditory feedback may be used to help regulate voice F0 during production of bi-tonal Mandarin phrases.

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 responses to changes in pitch of voice or tone auditory feedback

The present study was undertaken to examine if a subjects voice F0 responded not only to perturbations in pitch of voice feedback but also to changes in pitch of a side tone presented congruent with voice feedback. Small magnitude brief duration perturbations in pitch of voice or tone auditory feedback were randomly introduced during sustained vowel phonations. Results demonstrated a higher rate and larger magnitude of voice F0 responses to changes in pitch of the voice compared with a triangular-shaped tone (experiment 1) or a pure tone (experiment 2). However, response latencies did not differ across voice or tone conditions. Data suggest that subjects responded to the change in F0 rather than harmonic frequencies of auditory feedback because voice F0 response prevalence, magnitude, or latency did not statistically differ across triangular-shaped tone or pure-tone feedback. Results indicate the audio-vocal system is sensitive to the change in pitch of a variety of sounds, which may represent a flexible system capable of adapting to changes in the subjects voice. However, lower prevalence and smaller responses to tone pitch-shifted signals suggest that the audio-vocal system may resist changes to the pitch of other environmental sounds when voice feedback is present.

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.

Voice F0 responses elicited by perturbations in pitch of auditory feedback in individuals that stutter and controls

This study aims to increase our understanding of the underlying mechanisms of vocal control in frequency‐altered conditions of auditory feedback for people who do and who do not stutter by assessing the vocal responses to perturbations in pitch of auditory feedback. Past research has shown that the speech of people who stutter improves during frequency‐altered feedback, but the mechanisms responsible for this fluency remain unclear. Typically, brief modulations in pitch of voice auditory feedback lead to short‐latency corrective voice F0 responses during sustained phonations and inflected speech in nonstuttering individuals. However, data are lacking regarding audio‐vocal control mechanisms in individuals that stutter. Brief upward (+) and downward (−) perturbations in pitch (50 or 600 cents in magnitude) lasting 200 ms in duration were introduced intermittently into vocalizing subjects auditory feedback. To date, N=3 moderate to severe developmental stutterers and N=3 age and gender matched control nonst...

Role of voice F0 production accuracy and pitch perception ability in modifying compensatory voice F0 responses during sustained vowel productions

The purpose of the present study is to assess whether subject characteristics in terms of voice F0 production accuracy and pitch perception ability are related to the ability to compensate in real‐time for altered auditory feedback. To assess the relationship of vocal production, pitch‐perception, and voice F0 error‐correction, a series of three tasks were completed by typical college‐age participants: (1) A pitch‐matching task where participants vocally matched the pitch of audible complex tones, (2) two‐tone forced choice pitch‐discrimination tasks where participants decided if complex tone pairs (200 ms duration for each tone) sounded the same or different, and (3) pitch‐shifting tasks where participants produced sustained vowel phonations, while listening to experimentally altered auditory feedback (brief 200 ms pitch perturbations of +/−20, 60, or 100 cents were introduced into the feedback). Dependent measures of pitch‐matching accuracy, pitch‐discrimination sensitivity, and variations in the latenc...

Voice F0 responses elicited by perturbations in pitch of auditory feedback during English speech and sustained vowels

Twenty‐one native speakers of American English were asked to repeatedly inflect the pitch of either the first or second syllable of an English speech phrase or produce non‐word sustained vowels while listening to amplified auditory feedback. Brief upward and downward perturbations in pitch of auditory feedback were introduced in real time shortly after vocal onset. Resultant changes in voice F0 due to perturbations in pitch were compared across vocal conditions and perturbation direction. Data indicated that auditory feedback was used in real‐time to stabilize voice F0 during both normal English speech and sustained vowels. Incomplete compensatory corrections in voice F0 due to the perturbations in pitch of auditory feedback were prevalent during both dynamic speech (gain: ∼12.7%) and static sustained vowel phonations (gain: ∼19.3%), and appear to be regulated by similar corrective mechanisms. However during dynamic speech, voice F0 was modulated across syllable boundaries in a task‐dependent manner accor...

Reaction time of voluntary modulations in voice F0 during sustained pitch vocalizations

In an attempt to more clearly understand the neural control of voice, a reaction time study was designed to investigate how rapidly normal subjects, i.e., nontrained singers, can voluntarily increase or decrease their voice fundamental frequency (F0) during sustained vocalizations when cued with a 1000‐Hz auditory tone stimulus. Results revealed that overall reaction times (RTs) (F=21.9, df=2, 150, p=0.01) for upward F0 modulations occurred faster (range: 138–176 ms) than downward responses (range: 196–234 ms). In contrast to the reaction time findings, slightly higher peak velocities were observed for downward responses compared to upward responses. Shorter RTs observed for F0 elevation are therefore possibly related to central mechanisms involved in the planning of or execution of the direction in which F0 is to be modulated instead of muscle biomechanics. The fastest RTs obtained from the present study (138 ms) are slightly longer than the reflex latencies of the initial pitch‐shift reflex response (10...

Improvements in methodology for the pitch‐shifting technique

In recent years several studies have been published on voice control that utilized the pitch‐shifting technique. The technique requires averaging of multiple vocalizations to repeated presentations of pitch‐shifted feedback in order to eliminate random fluctuations in voice fundamental frequency. Time‐locked reflexive responses to a stimulus parameter are observed quite clearly after averaging. The present study was undertaken to improve the pitch‐shift methodology for data acquisition and analysis. Auditory pitch stimuli were presented at rates of 10, 5, and 2 per 5‐sec vocalization, as opposed to previous studies that used one stimulus per vocalization. Results of testing these rates of stimulus presentation on a group of 22 subjects indicated there was no difference in reflex magnitude or latency between the present methods and rates up to 5/vocalization. Rates of 10/vocalization led to a reduction in reflex magnitude. Using the 5/vocalization rate, it was possible to reduce the number of vocalizations...