Sex-related differences in vocal responses to pitch feedback perturbations during sustained vocalization

The present study assessed the effect of sex on voice fundamental frequency (F(0)) responses to pitch feedback perturbations during sustained vocalization. Sixty-four native-Mandarin speakers heard their voice pitch feedback shifted at ± 50, ± 100, or ± 200 cents for 200 ms, five times during each vocalization. The results showed that, as compared to female speakers, male speakers produced significantly larger but slower vocal responses to the pitch-shifted stimuli. These findings reveal a modulation of vocal response as a function of sex, and suggest that there may be a differential processing of vocal pitch feedback perturbations between men and women.     

Laryngeal electromyographic responses to perturbations in voice pitch auditory feedback

The present study was conducted to test the hypothesis that intrinsic laryngeal muscles are involved in producing voice fundamental frequency (F(0)) responses to perturbations in voice pitch auditory feedback. Electromyography (EMG) recordings of the cricothyroid and thyroarytenoid muscles were made with hooked-wire electrodes, while subjects sustained vowel phonations at three different voice F(0) levels (conversational, high pitch in head register, and falsetto register) and received randomized pitch shifts (±100 or ±300 cents) in their voice auditory feedback. The median latencies from stimulus onset to the peak in the EMG and voice F(0) responses were 167 and 224 ms, respectively. Among the three different F(0) levels, the falsetto register produced compensatory EMG responses that occurred prior to vocal responses and increased along with rising voice F(0) responses and decreased for falling F(0) responses. For the conversational and high voice levels, the EMG response timing was more variable than in the falsetto voice, and changes in EMG activity with relevance to the vocal responses did not follow the consistent trend observed in the falsetto condition. The data from the falsetto condition suggest that both the cricothyroid and thyroarytenoid muscles are involved in generating the compensatory vocal responses to pitch-shifted voice feedback.     

Voice responses to changes in pitch of voice or tone auditory feedback

The present study was undertaken to examine if a subject's 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 subject's 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.     

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.     

Compensatory responses to loudness-shifted voice feedback during production of Mandarin speech

Previous studies have demonstrated that perturbations in voice pitch or loudness feedback lead to compensatory changes in voice F(0) or amplitude during production of sustained vowels. Responses to pitch-shifted auditory feedback have also been observed during English and Mandarin speech. The present study investigated whether Mandarin speakers would respond to amplitude-shifted feedback during meaningful speech production. Native speakers of Mandarin produced two-syllable utterances with focus on the first syllable, the second syllable, or none of the syllables, as prompted by corresponding questions. Their acoustic speech signal was fed back to them with loudness shifted by +/-3 dB for 200 ms durations. The responses to the feedback perturbations had mean latencies of approximately 142 ms and magnitudes of approximately 0.86 dB. Response magnitudes were greater and latencies were longer when emphasis was placed on the first syllable than when there was no emphasis. Since amplitude is not known for being highly effective in encoding linguistic contrasts, the fact that subjects reacted to amplitude perturbation just as fast as they reacted to F(0) perturbations in previous studies provides clear evidence that a highly automatic feedback mechanism is active in controlling both F(0) and amplitude of speech production.     

Voice F0 responses to pitch-shifted voice feedback during English speech

Previous studies have demonstrated that motor control of segmental features of speech rely to some extent on sensory feedback. Control of voice fundamental frequency (F0) has been shown to be modulated by perturbations in voice pitch feedback during various phonatory tasks and in Mandarin speech. The present study was designed to determine if voice Fo is modulated in a task-dependent manner during production of suprasegmental features of English speech. English speakers received pitch-modulated voice feedback (+/-50, 100, and 200 cents, 200 ms duration) during a sustained vowel task and a speech task. Response magnitudes during speech (mean 31.5 cents) were larger than during the vowels (mean 21.6 cents), response magnitudes increased as a function of stimulus magnitude during speech but not vowels, and responses to downward pitch-shift stimuli were larger than those to upward stimuli. Response latencies were shorter in speech (mean 122 ms) compared to vowels (mean 154 ms). These findings support previous research suggesting the audio vocal system is involved in the control of suprasegmental features of English speech by correcting for errors between voice pitch feedback and the desired F0.     

Measuring the rate of change of voice fundamental frequency in fluent speech during mental depression

A method of measuring the rate of change of fundamental frequency has been developed in an effort to find acoustic voice parameters that could be useful in psychiatric research. A minicomputer program was used to extract seven parameters from the fundamental frequency contour of tape-recorded speech samples: (1) the average rate of change of the fundamental frequency and (2) its standard deviation, (3) the absolute rate of fundamental frequency change, (4) the total reading time, (5) the percent pause time of the total reading time, (6) the mean, and (7) the standard deviation of the fundamental frequency distribution. The method is demonstrated on (a) a material consisting of synthetic speech and (b) voice recordings of depressed patients who were examined during depression and after improvement.     

Relative contributions of temporal and place pitch cues to fundamental frequency discrimination in cochlear implantees

The effect of the filter bank on fundamental frequency (F0) discrimination was examined in four Nucleus CI24 cochlear implant subjects for synthetic stylized vowel-like stimuli. The four tested filter banks differed in cutoff frequencies, amount of overlap between filters, and shape of the filters. To assess the effects of temporal pitch cues on F0 discrimination, temporal fluctuations were removed above 10 Hz in one condition and above 200 Hz in another. Results indicate that F0 discrimination based upon place pitch cues is possible, but just-noticeable differences exceed 1 octave or more depending on the filter bank used. Increasing the frequency resolution in the F0 range improves the F0 discrimination based upon place pitch cues. The results of F0 discrimination based upon place pitch agree with a model that compares the centroids of the electrical excitation pattern. The addition of temporal fluctuations up to 200 Hz significantly improves F0 discrimination. Just-noticeable differences using both place and temporal pitch cues range from 6% to 60%. Filter banks that do not resolve the higher harmonics provided the best temporal pitch cues, because temporal pitch cues are clearest when the fluctuation on all channels is at F0 and preferably in phase.     

Effect of noise on the detectability and fundamental frequency discrimination of complex tones

Percent correct performance for discrimination of the fundamental frequency (0) of a complex tone was measured as a function of the level of a background pink noise (using fixed values of the difference in F0, deltaF0) and compared with percent correct performance for detection of the complex tone in noise, again as a function of noise level. The tone included some low, resolvable components, but not the fundamental component. The results were used to test the hypothesis that the worsening in F0 discrimination with increasing noise level was caused by the reduced detectability of the tone rather than by reduced precision of the internal representation of F0. For small values of deltaF0, the hypothesis was rejected because measured performance fell below that predicted by the hypothesis. However, this was true only for high noise levels, within 2-4.5 dB of the level required for masked threshold. The results indicate that the mechanism for extracting the F0 of a complex tone with resolved harmonics is remarkably robust. They also indicate that adding a background noise to a complex tone containing resolved harmonics is not a good means for equating its pitch salience with that of a complex tone containing only unresolved harmonics.     

Effect of artificially lengthened vocal tract on vocal fold oscillation's fundamental frequency.

The fundamental frequency of vocal fold oscillation (F(0)) is controlled by laryngeal mechanics and aerodynamic properties. F(0) change per unit change of transglottal pressure (dF/dP) using a shutter valve has been studied and found to have nonlinear, V-shaped relationship with F(0). On the other hand, the vocal tract is also known to affect vocal fold oscillation. This study examined the effect of artificially lengthened vocal tract length on dF/dP. dF/dP was measured in six men using two mouthpieces of different lengths. Results: The dF/dP graph for the longer vocal tract was shifted leftward relative to the shorter one. Conclusion: Using the one-mass model, the nadir of the "V" on the dF/dP graph was strongly influenced by the resonance around the first formant frequency. However, a more precise model is needed to account for the effects of viscosity and turbulence.     

Effect of duration on the frequency discrimination of individual partials in a complex tone and on the discrimination of fundamental frequency

Thresholds for the discrimination of fundamental frequency (FODLs) and frequency difference limens (FDLs) for individual partials within a complex tone (F0=250 Hz, harmonics 1-7) were measured for stimulus durations of 200, 50, and 16 ms. The FDLs increased with decreasing duration. Although the results differed across subjects, the effect of duration generally decreased as the harmonic number increased from 1 to 4, then increased as the harmonic number increased to 6, and finally decreased for the seventh harmonic. For each duration, FODLs were smaller than the smallest FDL for any individual harmonic, indicating that information is combined across harmonics in the discrimination of FO. FODLs predicted from the FDLs corresponded well with observed FODLs for the 200- and 16-ms durations but were significantly larger than observed FODLs for the 50-ms duration. A supplementary pitch-matching experiment using two subjects indicated that the contribution of the seventh harmonic to the pitch of the 16-ms complex tone was smaller than would be predicted from the FDL for that harmonic. The results are consistent with the idea that the dominant region shifts upward with decreasing duration, but that the weight assigned to individual harmonics is not always adjusted in an optimal way.     

Effect of perturbations in an active medium on the instability of the difference frequency of laser radiation

A frequency-stabilized helium-neon laser with Zeeman frequency splitting in the magnetic field was studied. A series of pulses with repetition frequency equal to the frequency difference caused by the splitting of the gain profile by the magnetic field was used as a reference signal for a laser interferometer. The modulation of discharge current by electric noise or natural oscillations of the discharge current were found to lengthen the edges of these pulses, which decreases the accuracy of measurements with a laser interferometer.     

Phonatory control in male singing: A study of the effects of subglottal pressure, fundamental frequency, and mode of phonation on the voice source

This article describes experiments carried out in order to gain a deeper understanding of the mechanisms underlying variation of vocal loudness in singers. Ten singers, two of whom are famous professional opera tenor soloists, phonated at different pitches and different loudnesses. Their voice source characteristics were analyzed by inverse filtering the oral airflow signal. It was found that the main physiological variable underlying loudness variation is subglottal pressure (Ps). The voice source property determining most of the loudness variation is the amplitude of the negative peak of the differentiated flow signal, as predicted by previous research. Increases in this amplitude are achieved by (a) increasing the pulse amplitude of the flow waveform; (b) moving the moment of vocal fold contact earlier in time, closer to the center of the pulse; and (c) skewing the pulses. The last mentioned alternative seems dependent on both Ps and the ratio between the fundamental frequency and the first formant. On the average, the singers doubled Ps when they increased fundamental frequency by one octave, and a doubling of the excess Ps over threshold caused the sound pressure level (SPL) to increase by 8–9 dB for neutral phonation, less if mode of phonation was changed to pressed. A shift of mode of phonation from flow over neutral to pressed was associated with a reduction of the peak glottal permittance i.e., the ratio between peak transglottal airflow to Ps. Flow phonation had the most favorable relationship between Ps and SPL.     

Effects of fundamental frequency and vocal-tract length changes on attention to one of two simultaneous talkers

Three experiments used the Coordinated Response Measure task to examine the roles that differences in F0 and differences in vocal-tract length have on the ability to attend to one of two simultaneous speech signals. The first experiment asked how increases in the natural F0 difference between two sentences (originally spoken by the same talker) affected listeners' ability to attend to one of the sentences. The second experiment used differences in vocal-tract length, and the third used both F0 and vocal-tract length differences. Differences in F0 greater than 2 semitones produced systematic improvements in performance. Differences in vocal-tract length produced systematic improvements in performance when the ratio of lengths was 1.08 or greater, particularly when the shorter vocal tract belonged to the target talker. Neither of these manipulations produced improvements in performance as great as those produced by a different-sex talker. Systematic changes in both F0 and vocal-tract length that simulated an incremental shift in gender produced substantially larger improvements in performance than did differences in F0 or vocal-tract length alone. In general, shifting one of two utterances spoken by a female voice towards a male voice produces a greater improvement in performance than shifting male towards female. The increase in performance varied with the intonation patterns of individual talkers, being smallest for those talkers who showed most variability in their intonation patterns between different utterances.