Vocal Perturbation Research Articles

Effects of low-frequency repetitive transcranial magnetic stimulation in adductor laryngeal dystonia: a safety, feasibility, and pilot study

PurposeThe effects of neuromodulation are virtually unexplored in adductor laryngeal dystonia (AdLD), a disorder characterized by involuntary contraction of intrinsic laryngeal muscles. Recent findings indicated that intracortical inhibition is reduced in people with AdLD. Low-frequency repetitive transcranial magnetic stimulation (rTMS) induces prolonged intracortical inhibition, but the effects in AdLD are unexplored. This pilot and feasibility study aimed to examine the safety, feasibility, and effects of a single session 1 Hz rTMS over the laryngeal motor cortex (LMC) in people with AdLD and healthy individuals.MethodsThe stimulation location was individualized and determined through TMS-evoked responses in the thyroarytenoid muscles using fine-wire electrodes. 1200 pulses of 1 Hz rTMS were delivered to the left LMC in two groups: Control (n = 6) and AdLD (n = 7). Tolerance, adverse effects, intracortical inhibition, and voice recordings were collected immediately before and after rTMS. Voice quality was assessed with acoustic-based and auditory-perceptual measures.ResultsAll participants tolerated the procedures, with no unexpected adverse events or worsening of symptoms. No significant effects on intracortical inhibition were observed. In the AdLD group, there was a large-effect size after rTMS in vocal perturbation measures and a small-effect size in decreased phonatory breaks.ConclusionsOne rTMS session over the LMC is safe and feasible, and demonstrated trends of beneficial effects on voice quality and phonatory function in AdLD. These preliminary findings support further investigation to assess clinical benefits in a future randomized sham-controlled trial.ClinicalTrials.govNCT02957942, registered on November 8, 2016.

Human Stress Detection: Cortisol Levels in Stressed Speakers Predict Voice-Based Judgments of Stress.

Despite recent evidence of a positive relationship between cortisol levels and voice pitch in stressed speakers, the extent to which human listeners can reliably judge stress from the voice remains unknown. Here, we tested whether voice-based judgments of stress co-vary with the free cortisol levels and vocal parameters of speakers recorded in a real-life stressful situation (oral examination) and baseline (2 weeks prior). Hormone and acoustic analyses indicated elevated salivary cortisol levels and corresponding changes in voice pitch, vocal tract resonances (formants), and speed of speech during stress. In turn, listeners' stress ratings correlated significantly with speakers' cortisol levels. Higher pitched voices were consistently perceived as more stressed; however, the influence of formant frequencies, vocal perturbation and noise parameters on stress ratings varied across contexts, suggesting that listeners utilize different strategies when assessing calm versus stressed speech. These results indicate that nonverbal vocal cues can convey honest information about a speaker's underlying physiological level of stress that listeners can, to some extent, detect and utilize, while underscoring the necessity to control for individual differences in the biological stress response.

Effect of the vocal tract filtering on the measurement of vocal cycle perturbations

Jitter and shimmer appear as symptoms of disordered voices and they are defined as the cycle-to-cycle variation of the cycle length and cycle amplitude, respectively. The frequency modulation of the phonatory excitation, i.e. vocal jitter, causes amplitude modulation (shimmer) of the speech signal due to the action of the vocal tract transfer function. In this Letter, the authors investigate the extent to which the vocal tract filtering affects the accuracy of measurement of vocal cycle perturbations of the phonatory excitation. To achieve this goal, the direct digital synthesiser is used to generate a series of glottal excitation cycles with the desired amount of vocal perturbations that crosses the vocal tract model to produce a set of 231 stimuli of sustained vowels [a]. Praat is used to measure the amount of perturbations. Results show that the values of the input shimmer inserted in the glottal excitation are smaller than the values measured by Praat. An undesired amount of shimmer is generated in the speech signal when the glottal excitation signal perturbed with jitter crosses through the vocal tract.

Comparison Between Patient-Perceived Voice Changes and Quantitative Voice Measures in the First Postoperative Year After Thyroidectomy

Voice changes after thyroidectomy are typically attributed to recurrent laryngeal nerve injury. However, most postoperative voice changes occur in the absence of clinically evident vocal fold paralysis. To date, no study has compared the prevalence, duration, and consequences of voice-related disability from the patient perspective with use of quantitative vocal measures. To assess the quality-of-life consequences of postthyroidectomy voice change from the perspective of patients with thyroid cancer and to compare patient-perceived voice changes with changes in quantitative vocal variables at 5 time points in the first postoperative year. This prospective mixed methods observational study within a randomized clinical trial occurred at the University of Wisconsin Hospital and Clinics. Participants were 42 patients with clinically node-negative papillary thyroid cancer without a preexisting vocal cord paralysis who were recruited and enrolled from outpatient clinics between June 6, 2014, and March 6, 2017, as part of the ongoing randomized clinical trial. Total thyroidectomy. Semistructured interviews, symptom prevalence, and instrumental voice evaluations (laryngoscopy, phonation threshold pressure, Dysphonia Severity Index, and Voice Handicap Index) occurred at baseline (n = 42) and 2-week (n = 42), 6-week (n = 39), 6-month (n = 35), and 1-year (n = 30) postoperative time points. Participants had a mean age of 48 years (interquartile range, 38-58 years; age range, 22-70 years) and were mostly female (74% [31 of 42]) and of white race/ethnicity (98% [41 of 42]). Impaired communication was the primary theme derived from patient interviews from before thyroidectomy to after thyroidectomy. Voice changes were perceived by 24 participants at 2 weeks after thyroidectomy. After surgery, voice symptoms were prevalent and persisted for 50% (21 of 42) of participants out to at least 1 year of follow-up. Quantitative vocal perturbations were detected in the Dysphonia Severity Index and Voice Handicap Index at the 2-week follow-up but returned to baseline levels by the 6-week follow-up visit. Voice changes are common after surgery for papillary thyroid cancer and affect quality of life for many patients out to 1 year of follow-up. Directly querying patients about postoperative voice changes and questioning whether commonly used aerodynamic and acoustic variables detect meaningful voice changes are important in identifying patients whose quality of life has been affected by postthyroidectomy dysphonia. ClinicalTrials.gov Identifier: NCT02138214.

Acoustic speech analysis of patients with decompensated heart failure: A pilot study.

This pilot study used acoustic speech analysis to monitor patients with heart failure (HF), which is characterized by increased intracardiac filling pressures and peripheral edema. HF-related edema in the vocal folds and lungs is hypothesized to affect phonation and speech respiration. Acoustic measures of vocal perturbation and speech breathing characteristics were computed from sustained vowels and speech passages recorded daily from ten patients with HF undergoing inpatient diuretic treatment. After treatment, patients displayed a higher proportion of automatically identified creaky voice, increased fundamental frequency, and decreased cepstral peak prominence variation, suggesting that speech biomarkers can be early indicators of HF.

Correlation of the Iranian Voice Quality of Life Profile (IVQLP) with Acoustic Measurements across Three Common Voice Disorders

The Iranian Voice Quality of Life Profile (IVQLP) is a recent culture-based developed tool for assessing the quality of life of dysphonic patients. The research questions addressed here are as follows: (1) Are the correlations between IVQLP scores and values of objective voice measures? (2) Do the correlations differ across the three different voice disorders? The subjects were divided into three groups: muscle tension dysphonia (MTD) (n = 62), benign midmembranous vocal fold lesions (n = 56), and unilateral vocal fold paralysis (UVFP) (n = 32). The study sample consisted of 91 males and 59 females. The individuals had a mean age of 46.53 ± 13.84 years. All of the participants completed the IVQLP questionnaire. The PRAAT software was used to provide acoustic analyses. The correlations between fundamental frequency (F0), perturbation analyses, harmonics-to-noise ratio, and IVQLP data of the three groups of patients were measured using Pearson's correlation. There was a significant correlation between the total score and jitter in the MTD group. For the benign vocal fold lesion group, correlations were significant and relatively strong for numerous analyses. Again, there were numerous significant and strong correlations for the UVFP group. Results may indicate two interpretations. One interpretation of the results is that patients with morphological tissue changes (lesions, paralysis) appear to associate their sense of how their voice problem negatively affects their lives. A second interpretation is that there is perhaps a threshold of vocal perturbation or instability that lends itself to a patient's connection to his or her sense of how the voice affects his or her quality of life.

Measurement of signal-to-noise ratio in dysphonic voices by image processing of spectrograms

The measurement of glottal noise was investigated in human and synthesized dysphonic voices by means of two-dimensional (2D) speech processing. A prime objective was the reduction of measurement sensitivities to fundamental frequency (f0) tracking errors and phonatory aperiodicities. An available fingerprint image enhancement algorithm was used for signal-to-noise measurement in narrow band spectrographic images. This spectrographic signal-to-noise ratio estimation method (S2NR) creates binary masks, mainly based on the orientation field of the partials, to separate energy in regions with strong harmonics from energy in noisy areas. Synthesized vowels with additive noise were used to calibrate the algorithm, validate the calibration, and systematically evaluate its dependence on f0, shimmer (cycle-to-cycle amplitude perturbation), and jitter (cycle-to-cycle f0 perturbation). In synthesized voices with known signal-to-noise ratios in the 5–40dB range, S2NR estimates were, on average, accurate within ±3.2dB and robust to variations in f0 (120Hz or 220Hz), jitter (0–3%), and shimmer (0–30%). In human /a/ produced by dysphonic speakers, S2NR values and perceptual ratings of breathiness revealed a non-linear but monotonic decay of S2NR with increased breathiness. Comparison between S2NR and related acoustic measurements indicated similar behaviors regarding the relationship with breathiness and immunity to shimmer, but the other methods had marked influence of jitter. Overall, the S2NR method did not rely on accurate f0 estimation, was robust to vocal perturbations and largely independent of vowel type, having also potential application in running speech.

The Effect of Smoking on the Dysphonia Severity Index in Females

Objective: This study investigated the capability of the Dysphonia Severity Index (DSI) and its component measures to reveal differences in vocal capability between groups of young adult female smokers and nonsmokers. Patients and Methods: The subjects were 30 female nonsmokers and 30 female smokers between the ages of 18 and 24 years. Data on the DSI components (maximum phonation time, MPT; highest phonational frequency, F_{0 high}; lowest intensity, I_low, and jitter) were collected, followed by calculation of the DSI. Results: Significant differences between groups were observed on the DSI, with reduced DSI scores in smokers primarily due to reductions in F_{0 high} and increases in I_low. A strong partial correlation between MPT and the DSI in smokers may be indicative of reductions in respiratory support and/or phonatory control. Conclusions: Significant group differences in the DSI and component measures may be indicative of early changes in vocal function secondary to smoking. Reductions in frequency and dynamic range are consistent with the possibility of increased vocal fold mass in smokers. The results indicate that significant differences in the DSI between groups may be observed in subjects with perceptually normal vocal quality and with normal levels of vocal perturbation.

Decomposition of Vocal Cycle Length Perturbations into Vocal Jitter and Vocal Microtremor, and Comparison of Their Size in Normophonic Speakers

Summary: A statistical method that enables raw vocal cycle length perturbations to be decomposed into perturbations ascribed to vocal jitter and vocal tremor is presented, together with a comparison of the size of jitter and tremor. The method is based on a time series model that splits the vocal cycle length perturbations into uncorrelated cycle-to-cycle perturbations ascribed to vocal jitter and supra-cycle perturbations ascribed to vocal tremor. The corpus was composed of 114 vocal cycle length time series for sustained vowels [a], [i], and [u] produced by 22 male and 16 female normophonic speakers. The results were the following. First, 100 out of 114 time series were decomposed successfully by means of the time series model. Second, vocal perturbations ascribed to tremor were significantly larger than perturbations ascribed to jitter. Third, the correlation between vocal jitter and vocal tremor was moderate, but statistically significant. Fourth, small but statistically significant differences were observed among the three vowel timbres in the relative jitter and the arithmetic difference of jitter and tremor. Fifth, the differences between male and female speakers were not statistically significant in the relative raw perturbations, the relative jitter, or the modulation level owing to tremor.

Psychoacoustical evaluation of PSOLA. II. Double-formant stimuli and the role of vocal perturbation.

This article presents the results of listening experiments and psychoacoustical modeling aimed at evaluating the pitch synchronous overlap-and-add (PSOLA) technique. This technique can be used for simultaneous modification of pitch and duration of natural speech, using simple and efficient time-domain operations on the speech waveform. The first set of experiments tested the ability of subjects to discriminate double-formant stimuli, modified in fundamental frequency using PSOLA, from unmodified stimuli. Of the potential auditory discrimination cues induced by PSOLA, cues from the first formant were found to generally dominate discrimination performance. In the second set of experiments the influence of vocal perturbation, i.e., jitter and shimmer, on discriminability of PSOLA-modified single-formant stimuli was determined. The data show that discriminability deteriorates at most modestly in the presence of jitter and shimmer. With the exception of a few conditions, the trends in these data could be replicated by either using a modulation-discrimination or an intensity-discrimination model, dependent on the formant frequency. As a baseline experiment detection thresholds for jitter and shimmer were measured. Thresholds for jitter could be replicated by using either the modulation-discrimination or the intensity-discrimination model, dependent on the (mean) fundamental frequency of stimuli. The thresholds for shimmer could be accurately predicted for stimuli with a 250-Hz fundamental, but less accurately in the case of a 100-Hz fundamental.

Clinical relevance of the fractal dimension of F 0perturbations computed by the box-counting method

The box-counting method for determining the fractal dimension (Dfj) was applied to the fundamental frequency (F0) perturbations in normal and pathological voices in order to assess its clinical value. The upper limit of these Dfj values was similar for both groups, but the distribution for pathological voices extended to lower values than for the normal voices. However, these lower values were most probably the result of one or a few outlying frequency points due to incorrect determination of the vocal period. The Dfj of normal voices were within the range of values found for randomly varying F0 values. It was concluded, that the vocal perturbations in pathological voices are also more or less randomly distributed. So, the Dfj, at that least determined with the box-counting method, do not contain clinically relevant information in addition to the traditional measures for the extent of the vocal period perturbations. An exception is special perturbation types like diplophonia. The result of the computation is very sensitive for voice breaks and vibrato and depends on the number of periods.

Comparisons of jitter, shimmer, and signal-to-noise ratio from directly digitized versus taped voice samples

The purpose of this study was to compare jitter, shimmer, and signal-to-noise ratio (SNR) measures obtained from tape-recorded samples with the same measures made on directly digitized voice samples, with use of the CSpeech acoustic analysis program. Subjects included 30 young women who phonated the vowel /a/ at a comfortable pitch and loudness level. Voice samples were simultaneously recorded and digitized, and the resulting perturbation measures for the two conditions were compared. Results indicated that there were small but statistically significant differences between percent jitter, percent shimmer, and SNR calculated from taped samples compared with the same measures calculated from directly digitized samples. It was concluded that direct digitization for clinical measures of vocal perturbation was most desirable, but that taped samples could be used, if necessary, with some caution.

Speaker race identification from acoustic cues in the vocal signal.

One-second acoustic samples were extracted from the mid-portion of sustained /a/ vowels produced by 50 black and 50 white adult males. Each vowel sample from a black subject was randomly paired with a sample from a white subject. From the tape-recorded samples alone, both expert and naive listeners could determine the race of the speaker with 60% accuracy. The accuracy of race identification was independent of the listener's own race, sex, or listening experience. An acoustic analysis of the samples revealed that, although within ranges reported by previous studies of normal voices, the black speakers had greater frequency perturbation, significantly greater amplitude perturbation, and a significantly lower harmonics-to-noise ratio than did the white speakers. The listeners were most successful in distinguishing voice pairs when the differences in vocal perturbation and additive noise were greatest and were least successful when such differences were minimal or absent. Because there were no significant differences in the mean fundamental frequency or formant structure of the voice samples, it is likely that the listeners relied on differences in spectral noise to discriminate the black and white speakers.

Time-shift, trial, and gender effects on vocal perturbation measures

Three jitter and three shimmer measures were examined for: (1) the stability of the measured values with respect to shifts in sample site (starting point of window in the token) and (2) the effects of trial and gender. The perturbation measures and their coefficients of variation for windows starting from five different but adjacent cycles showed a dependence on sample size. Their variability with regard to shifts in sample site decreased asymptotically with increasing size. The data suggested no statistically significant trial effect except for APQ and no statistically significant gender effect except for absolute jitter. It is speculated that relatively long smoothing windows for shimmer (such as the one used for APQ) would allow the effects of slow vocal modulations (e.g., tremor) to accentuate, especially for lower pitch speakers.

Effects of initial consonant, pneumotachographic mask, and oral pressure tube on vocal perturbation, harmonics-to-noise, and intensity measurements

Summary Vocal perturbation, harmonics-to-noise, and intensity measures were obtained for 10 subjects during three experimental tasks: (a) prolonged /a/, (b) /pa/ with vowel prolonged, and (c) same as (b) with subjects wearing a pneumotachographic mask and oral pressure tube inserted between the lips. There were no statistically significant differences among the experimental conditions for any of the measures. The findings suggest that a single task may be used to obtain airflow, oral pressure, and acoustic measures of vocal performance. Observed differences in jitter and harmonic-to-noise means for the male and female speakers are discussed.

Acoustic waveform perturbations and voice disorders

Summary Small and apparently random perturbations of the vocal waveform's period and amplitude (referred to as jitter and shimmer, respectively) have received a great deal of attention. Automatic extraction methods make assessment of vocal perturbation a potential part of routine clinical assessments. Careful attention will have to be paid to several technological issues, particularly to the quality of recorded voice samples used for this kind of analysis. Better databases must be developed, and the underlying voice physiology requires clarification

Preliminary evaluation of selected acoustic and glottographic measures for clinical phonatory function analysis

Summary Acoustic and glottographic measures may provide important information that could enhance clinical management and documentation of vocal dysfunction. Acoustic measures such as jitter and shimmer reflect “short-term” perturbations, or instabilities of the voice, and the coefficients of variation for frequency and for amplitude reflect “long-term” perturbations. Interpretations of these acoustic measures are based on the assumption that vocal perturbations may be related to laryngeal tissue abnormalities, asymmetries in vocal fold movement, or neuromuscular fluctuations in the respiratory, laryngeal, or vocal tract systems. The abduction quotient is a glottographic measure related to laryngeal adduction and is obtained from an analysis of the electroglottograph signal. The adduction measure appears to be independent of the acoustic perturbation measures. Interpretations of the acoustic and adductory measures may, therefore, complement each other for greater understanding of a patient's laryngeal behavior. Visual displays of the acoustic and glottographic signals also are discussed to demonstrate their value in voice signal interpretations. Case studies illustrate potential interpretations of the acoustic perturbation and abduction quotient measures.

Preliminary experiments on voice screening

An acoustic voice evaluation system has been developed on a mini-computer, primarily aiming at its application to the screening of laryngeal pathology. The system is based on the acoustic measurements of vocal perturbations and noise components from the sustained utterance of the Japanese vowel /e/. Performance of the system is described by referring to the results of clinical voice screening experiments that were performed with 991 subjects for the possible presence of laryngeal cancer.