Do Not Cut Off Your Tail: A Mega-Analysis of Responses to Auditory Perturbation Experiments

PURPOSE

The practice of removing "following" responses from speech perturbation analyses is increasingly common, despite no clear evidence as to whether these responses represent a unique response type. This study aimed to determine if the distribution of responses to auditory perturbation paradigms represents a bimodal distribution, consisting of two distinct response types, or a unimodal distribution.

METHOD

This mega-analysis pooled data from 22 previous studies to examine the distribution and magnitude of responses to auditory perturbations across four tasks: adaptive pitch, adaptive formant, reflexive pitch, and reflexive formant. Data included at least 150 unique participants for each task, with studies comprising younger adult, older adult, and Parkinson's disease populations. A Silverman's unimodality test followed by a smoothed bootstrap resampling technique was performed for each task to evaluate the number of modes in each distribution. Wilcoxon signed-ranks tests were also performed for each distribution to confirm significant compensation in response to the perturbation.

RESULTS

Modality analyses were not significant (p > .05) for any group or task, indicating unimodal distributions. Our analyses also confirmed compensatory reflexive responses to pitch and formant perturbations across all groups, as well as adaptive responses to sustained formant perturbations. However, analyses of sustained pitch perturbations only revealed evidence of adaptation in studies with younger adults.

CONCLUSION

The demonstration of a clear unimodal distribution across all tasks suggests that following responses do not represent a distinct response pattern, but rather the tail of a unimodal distribution.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24282676.

A comparison of structural morphometry in children and adults with persistent developmental stuttering

This cross-sectional study aimed to differentiate earlier occurring neuroanatomical differences that may reflect core deficits in stuttering versus changes associated with a longer duration of stuttering by analysing structural morphometry in a large sample of children and adults who stutter and age-matched controls. Whole-brain T1-weighted structural scans were obtained from 166 individuals who stutter (74 children, 92 adults; ages 3-58) and 191 controls (92 children, 99 adults; ages 3-53) from eight prior studies in our laboratories. Mean size and gyrification measures were extracted using FreeSurfer software for each cortical region of interest. FreeSurfer software was also used to generate subcortical volumes for regions in the automatic subcortical segmentation. For cortical analyses, separate ANOVA analyses of size (surface area, cortical thickness) and gyrification (local gyrification index) measures were conducted to test for a main effect of diagnosis (stuttering, control) and the interaction of diagnosis-group with age-group (children, adults) across cortical regions. Cortical analyses were first conducted across a set of regions that comprise the speech network and then in a second whole-brain analysis. Next, separate ANOVA analyses of volume were conducted across subcortical regions in each hemisphere. False discovery rate corrections were applied for all analyses. Additionally, we tested for correlations between structural morphometry and stuttering severity. Analyses revealed thinner cortex in children who stutter compared with controls in several key speech-planning regions, with significant correlations between cortical thickness and stuttering severity. These differences in cortical size were not present in adults who stutter, who instead showed reduced gyrification in the right inferior frontal gyrus. Findings suggest that early cortical anomalies in key speech planning regions may be associated with stuttering onset. Persistent stuttering into adulthood may result from network-level dysfunction instead of focal differences in cortical morphometry. Adults who stutter may also have a more heterogeneous neural presentation than children who stutter due to their unique lived experiences.

The Relationships Among Vocal Variability, Vocal-Articulatory Coordination, and Dysphonia in Children

OBJECTIVE

The purpose of this study was to evaluate the relationship between vocal variability and variability of vocal-articulatory coordination in children. Furthermore, this study examined if this relationship was impacted by pediatric dysphonia.

STUDY DESIGN

Retrospective analysis of speech samples in the Arizona Child Acoustic Database.

METHODS

Speech samples from children 2-7 years of age were selected for analysis. Vocal variability was defined as the coefficient of variation (CoV) of fundamental frequency, taken from the center of sustained vowels. Variability of vocal-articulatory coordination was defined as the CoV of voice onset time (VOT) of voiceless stop consonants. Both objective and subjective measures of dysphonia were completed for each participant.

RESULTS

Children had a negative correlation between VOT variability and vocal variability. Further analysis indicated that this relationship was present in children with typical developmental levels of dysphonia but absent for children with moderate to severe dysphonia. Increased dysphonia severity was associated with increased vocal variability.

CONCLUSION

Increased VOT variability was associated with decreased vocal variability in children with dysphonia severities consistent with typical vocal development. However, this relationship was not present in children with moderate to severe dysphonia. This study suggests that future work is needed to examine the relationships between the vocal system and vocal-articulatory coordination in children with and without diagnosed voice disorders.

Quantitatively characterizing reflexive responses to pitch perturbations

Background

Reflexive pitch perturbation experiments are commonly used to investigate the neural mechanisms underlying vocal motor control. In these experiments, the fundamental frequency–the acoustic correlate of pitch–of a speech signal is shifted unexpectedly and played back to the speaker via headphones in near real-time. In response to the shift, speakers increase or decrease their fundamental frequency in the direction opposing the shift so that their perceived pitch is closer to what they intended. The goal of the current work is to develop a quantitative model of responses to reflexive perturbations that can be interpreted in terms of the physiological mechanisms underlying the response and that captures both group-mean data and individual subject responses.

Methods

A model framework was established that allowed the specification of several models based on Proportional-Integral-Derivative and State-Space/Directions Into Velocities of Articulators (DIVA) model classes. The performance of 19 models was compared in fitting experimental data from two published studies. The models were evaluated in terms of their ability to capture both population-level responses and individual differences in sensorimotor control processes.

Results

A three-parameter DIVA model performed best when fitting group-mean data from both studies; this model is equivalent to a single-rate state-space model and a first-order low pass filter model. The same model also provided stable estimates of parameters across samples from individual subject data and performed among the best models to differentiate between subjects. The three parameters correspond to gains in the auditory feedback controller’s response to a perceived error, the delay of this response, and the gain of the somatosensory feedback controller’s “resistance” to this correction. Excellent fits were also obtained from a four-parameter model with an additional auditory velocity error term; this model was better able to capture multi-component reflexive responses seen in some individual subjects.

Conclusion

Our results demonstrate the stereotyped nature of an individual’s responses to pitch perturbations. Further, we identified a model that captures population responses to pitch perturbations and characterizes individual differences in a stable manner with parameters that relate to underlying motor control capabilities. Future work will evaluate the model in characterizing responses from individuals with communication disorders.

A Practical Guide to Calculating Cepstral Peak Prominence in Praat

The acoustic measure of cepstral peak prominence (CPP) is recommended for the analysis of dysphonia. Yet, clinical use of this measure is not universal, as clinicians and researchers are still learning the strengths and limitations of this measure. Furthermore, affordable access to specialized acoustic software is a significant barrier to universal CPP use. This article will provide a guide on how to calculate CPP in Praat, a free software program, using a new CPP plugin. Important external factors that could influence CPP measures are discussed, and suggestions for clinical use are provided. As CPP becomes more widely used by clinicians and researchers, it is important to consider external factors that may inadvertently influence CPP values. Controlling for these external factors will aid in reducing variability across CPP values, which will make CPP a valuable tool for both clinical and research purposes.

Increased Intra-Subject Variability of Neural Activity During Speech Production in People with Autism Spectrum Disorder

Background

Communication difficulties are a core deficit in many people with autism spectrum disorder (ASD). The current study evaluated neural activation in participants with ASD and neurotypical (NT) controls during a speech production task.

Methods

Neural activities of participants with ASD (N = 15, M = 16.7 years, language abilities ranged from low verbal abilities to verbally fluent) and NT controls (N = 12, M = 17.1 years) was examined using functional magnetic resonance imaging with a sparse-sampling paradigm.

Results

There were no differences between the ASD and NT groups in average speech activation or inter-subject run-to-run variability in speech activation. Intra-subject run-to-run neural variability was greater in the ASD group and was positively correlated with autism severity in cortical areas associated with speech.

Conclusions

These findings highlight the importance of understanding intra-subject neural variability in participants with ASD.

The Neural Circuitry Underlying the "Rhythm Effect" in Stuttering

Purpose Stuttering is characterized by intermittent speech disfluencies, which are dramatically reduced when speakers synchronize their speech with a steady beat. The goal of this study was to characterize the neural underpinnings of this phenomenon using functional magnetic resonance imaging. Method Data were collected from 16 adults who stutter and 17 adults who do not stutter while they read sentences aloud either in a normal, self-paced fashion or paced by the beat of a series of isochronous tones ("rhythmic"). Task activation and task-based functional connectivity analyses were carried out to compare neural responses between speaking conditions and groups after controlling for speaking rate. Results Adults who stutter produced fewer disfluent trials in the rhythmic condition than in the normal condition. Adults who stutter did not have any significant changes in activation between the rhythmic condition and the normal condition, but when groups were collapsed, participants had greater activation in the rhythmic condition in regions associated with speech sequencing, sensory feedback control, and timing perception. Adults who stutter also demonstrated increased functional connectivity among cerebellar regions during rhythmic speech as compared to normal speech and decreased connectivity between the left inferior cerebellum and the left prefrontal cortex. Conclusions Modulation of connectivity in the cerebellum and prefrontal cortex during rhythmic speech suggests that this fluency-inducing technique activates a compensatory timing system in the cerebellum and potentially modulates top-down motor control and attentional systems. These findings corroborate previous work associating the cerebellum with fluency in adults who stutter and indicate that the cerebellum may be targeted to enhance future therapeutic interventions. Supplemental Material https://doi.org/10.23641/asha.14417681.

Relationships between vocal pitch perception and production: a developmental perspective

The purpose of this study was to examine the relationships between vocal pitch discrimination abilities and vocal responses to auditory pitch-shifts. Twenty children (6.6-11.7 years) and twenty adults (18-28 years) completed a listening task to determine auditory discrimination abilities to vocal fundamental frequency (fo) as well as two vocalization tasks in which their perceived fo was modulated in real-time. These pitch-shifts were either unexpected, providing information on auditory feedback control, or sustained, providing information on sensorimotor adaptation. Children were subdivided into two groups based on their auditory pitch discrimination abilities; children within two standard deviations of the adult group were classified as having adult-like discrimination abilities (N = 11), whereas children outside of this range were classified as having less sensitive discrimination abilities than adults (N = 9). Children with less sensitive auditory pitch discrimination abilities had significantly larger vocal response magnitudes to unexpected pitch-shifts and significantly smaller vocal response magnitudes to sustained pitch-shifts. Children with less sensitive auditory pitch discrimination abilities may rely more on auditory feedback and thus may be less adept at updating their stored motor programs.

Relative Fundamental Frequency in Children With and Without Vocal Fold Nodules

Purpose Relative fundamental frequency (RFF) is an acoustic measure that is sensitive to functional voice differences in adults. The aim of the current study was to evaluate RFF in children, as there are known structural and functional differences between the pediatric and adult vocal mechanisms. Method RFF was analyzed in 28 children with vocal fold nodules (CwVN, M = 9.0 years) and 28 children with typical voices (CwTV, M = 8.9 years). RFF is the instantaneous fundamental frequency (f ₀) of the 10 vocalic cycles during devoicing (vocal offset) and 10 vocalic cycles during the revoicing (vocal onset) of the vowels that surround a voiceless consonant. Each cycle's f ₀ was normalized to a steady-state portion of the vowel. RFF values for the cycles closest to the voiceless consonant, that is, Offset Cycle 10 and Onset Cycle 1, were examined. Results Average RFF values for Offset Cycle 10 and Onset Cycle 1 did not differ between CwVN and CwTV; however, within-subject variability of Offset Cycle 10 was decreased in CwVN. Across both groups, male children had lower Offset Cycle 10 RFF values as compared to female children. Additionally, Onset Cycle 1 values were decreased in younger children as compared to those of older children. Conclusions Unlike previous work with adults, CwVN did not have significantly different RFF values than CwTV. Younger children had lower RFF values for Onset Cycle 1 than older children, suggesting that vocal onset f ₀ may provide information on the maturity of the laryngeal motor system.

Auditory Feedback Control Mechanisms Do Not Contribute to Cortical Hyperactivity Within the Voice Production Network in Adductor Spasmodic Dysphonia

Purpose Adductor spasmodic dysphonia (ADSD), the most common form of spasmodic dysphonia, is a debilitating voice disorder characterized by hyperactivity and muscle spasms in the vocal folds during speech. Prior neuroimaging studies have noted excessive brain activity during speech in participants with ADSD compared to controls. Speech involves an auditory feedback control mechanism that generates motor commands aimed at eliminating disparities between desired and actual auditory signals. Thus, excessive neural activity in ADSD during speech may reflect, at least in part, increased engagement of the auditory feedback control mechanism as it attempts to correct vocal production errors detected through audition. Method To test this possibility, functional magnetic resonance imaging was used to identify differences between participants with ADSD (n = 12) and age-matched controls (n = 12) in (a) brain activity when producing speech under different auditory feedback conditions and (b) resting-state functional connectivity within the cortical network responsible for vocalization. Results As seen in prior studies, the ADSD group had significantly higher activity than the control group during speech with normal auditory feedback (compared to a silent baseline task) in three left-hemisphere cortical regions: ventral Rolandic (sensorimotor) cortex, anterior planum temporale, and posterior superior temporal gyrus/planum temporale. Importantly, this same pattern of hyperactivity was also found when auditory feedback control of speech was eliminated through masking noise. Furthermore, the ADSD group had significantly higher resting-state functional connectivity between sensorimotor and auditory cortical regions within the left hemisphere as well as between the left and right hemispheres. Conclusions Together, our results indicate that hyperactivation in the cortical speech network of individuals with ADSD does not result from hyperactive auditory feedback control mechanisms and rather is likely related to impairments in somatosensory feedback control and/or feedforward control mechanisms.

A Simple 3-Parameter Model for Examining Adaptation in Speech and Voice Production

Sensorimotor adaptation experiments are commonly used to examine motor learning behavior and to uncover information about the underlying control mechanisms of many motor behaviors, including speech production. In the speech and voice domains, aspects of the acoustic signal are shifted/perturbed over time via auditory feedback manipulations. In response, speakers alter their production in the opposite direction of the shift so that their perceived production is closer to what they intended. This process relies on a combination of feedback and feedforward control mechanisms that are difficult to disentangle. The current study describes and tests a simple 3-parameter mathematical model that quantifies the relative contribution of feedback and feedforward control mechanisms to sensorimotor adaptation. The model is a simplified version of the DIVA model, an adaptive neural network model of speech motor control. The three fitting parameters of SimpleDIVA are associated with the three key subsystems involved in speech motor control, namely auditory feedback control, somatosensory feedback control, and feedforward control. The model is tested through computer simulations that identify optimal model fits to six existing sensorimotor adaptation datasets. We show its utility in (1) interpreting the results of adaptation experiments involving the first and second formant frequencies as well as fundamental frequency; (2) assessing the effects of masking noise in adaptation paradigms; (3) fitting more than one perturbation dimension simultaneously; (4) examining sensorimotor adaptation at different timepoints in the production signal; and (5) quantitatively predicting responses in one experiment using parameters derived from another experiment. The model simulations produce excellent fits to real data across different types of perturbations and experimental paradigms (mean correlation between data and model fits across all six studies = 0.95 ± 0.02). The model parameters provide a mechanistic explanation for the behavioral responses to the adaptation paradigm that are not readily available from the behavioral responses alone. Overall, SimpleDIVA offers new insights into speech and voice motor control and has the potential to inform future directions of speech rehabilitation research in disordered populations. Simulation software, including an easy-to-use graphical user interface, is publicly available to facilitate the use of the model in future studies.

Vocal Pitch Discrimination in Children with and without Vocal Fold Nodules

Vocal pitch discrimination abilities were compared in sixteen children with vocal fold nodules (CwVN) and sixteen matched controls with typical voices (CwTV). Vocal pitch discrimination was also evaluated in thirty-five vocally healthy children and twenty adults to examine potential changes as a function of maturation. CwTV were categorized as either younger (N = 15, 5.6-7.7 years) or older (N = 20, 8.2-11.7 years). Participants completed two-alternative, forced choice listening tasks in which they judged whether pairs of sustained /α/ tokens were different in pitch. Each pair consisted of a base token with a fundamental frequency fo ) of 216.2 Hz and a test token with a fo that was adaptively modified, according to the participant's prior judgments. There were no significant differences in pitch discrimination abilities between CwVN and CwTV. Pitch discrimination abilities were significantly poorer in younger and older CwTV as compared to adults. Additionally, younger CwTV had significantly poorer discrimination abilities than older CwTV. Findings from this study suggest that CwVN do not have differences in pitch discrimination abilities, yet, therapies designed for CwVN should consider this developmental trend in perceptual abilities.

Pitch Shifting With the Commercially Available Eventide Eclipse: Intended and Unintended Changes to the Speech Signal

Purpose This study details the intended and unintended consequences of pitch shifting with the commercially available Eventide Eclipse. Method Ten vocally healthy participants ( M = 22.0 years; 6 cisgender females, 4 cisgender males) produced a sustained /ɑ/, creating an input signal. This input signal was processed in near real time by the Eventide Eclipse to create an output signal that was either not shifted (0 cents), shifted +100 cents, or shifted -100 cents. Shifts occurred either throughout the entire vocalization or for a 200-ms period after vocal onset. Results Input signals were compared to output signals to examine potential changes. Average pitch-shift magnitudes were within 1 cent of the intended pitch shift. Measured pitch-shift length for intended 200-ms shifts was between 5.9% and 21.7% less than expected, based on the portion of shift selected for measurement. The delay between input and output signals was an average of 11.1 ms. Trials shifted +100 cents had a longer delay than trials shifted -100 or 0 cents. The first 2 formants (F1, F2) shifted in the direction of the pitch shift, with F1 shifting 6.5% and F2 shifting 6.0%. Conclusions The Eventide Eclipse is an accurate pitch-shifting hardware that can be used to explore voice and vocal motor control. The pitch-shifting algorithm shifts all frequencies, resulting in a subsequent change in F1 and F2 during pitch-shifted trials. Researchers using this device should be mindful of stimuli selection to avoid confusion during data interpretation.

Validation of an Algorithm for Semi-automated Estimation of Voice Relative Fundamental Frequency

OBJECTIVES

Relative fundamental frequency (RFF) has shown promise as an acoustic measure of voice, but the subjective and time-consuming nature of its manual estimation has made clinical translation infeasible. Here, a faster, more objective algorithm for RFF estimation is evaluated in a large and diverse sample of individuals with and without voice disorders.

METHODS

Acoustic recordings were collected from 154 individuals with voice disorders and 36 age- and sex-matched controls with typical voices. These recordings were split into training and 2 testing sets. Using an algorithm tuned to the training set, semi-automated RFF estimates in the testing sets were compared to manual RFF estimates derived from 3 trained technicians.

RESULTS

The semi-automated RFF estimations were highly correlated ( r = 0.82-0.91) with the manual RFF estimates.

CONCLUSIONS

Fast and more objective estimation of RFF makes large-scale RFF analysis feasible. This algorithm allows for future work to optimize RFF measures and expand their potential for clinical voice assessment.

The Impact of Glottal Configuration on Speech Breathing

OBJECTIVE

The purpose of this study was to examine whether changes in respiratory patterns occurred in response to volitional changes in glottal configuration.

METHODS

Twelve vocally healthy participants read a passage while wearing the Inductotrace respiratory inductive plethysmograph, which measures the excursions of the rib cage and abdomen. Participants read the passage 5 times in a typical speaking voice (baseline phase), 10 times in an experimental voice, which was similar to a breathy vocal quality (experimental phase), and 5 times again in a typical speaking voice (return phase). Kinematic estimates of lung volume (LV) initiation, LV termination, and LV excursion were collected for each speech breath.

RESULTS

Participants spoke with larger LV excursions during the experimental phase, characterized by increased LV initiation and decreased LV termination compared with the baseline phase.

CONCLUSION

In response to volitional changes in glottal configuration, healthy individuals spoke with increased LV excursion. They both responded to changes (decreasing LV termination) and planned for more efficient future utterances (increasing LV initiation) during the experimental phase. This study demonstrated that respiratory patterns change in response to changes in glottal configuration; future work will examine these patterns in individuals with voice disorders.

Relative Fundamental Frequency Distinguishes Between Phonotraumatic and Non-Phonotraumatic Vocal Hyperfunction

PURPOSE

The purpose of this article is to examine the ability of an acoustic measure, relative fundamental frequency (RFF), to distinguish between two subtypes of vocal hyperfunction (VH): phonotraumatic (PVH) and non-phonotraumatic (NPVH).

METHOD

RFF values were compared among control individuals with typical voices (N = 49), individuals with PVH (N = 54), and individuals with NPVH (N = 35).

RESULTS

Offset Cycle 10 RFF differed significantly among all 3 groups with values progressively decreasing for controls, individuals with NPVH, and individuals with PVH. Individuals with PVH also had lower Offset Cycles 8 and 9 relative to the other 2 groups and lower RFF values for Offset Cycle 7 relative to controls. There was also a trend for lower Onset Cycle 1 RFF values for the PVH group compared with the NPVH group.

CONCLUSIONS

RFF values were significantly different between controls and individuals with VH and also between the two subtypes of VH. This study adds further support to the notion that the differences between these two subsets of VH may be functional as well as structural.

The Relationship Between Relative Fundamental Frequency and a Kinematic Estimate of Laryngeal Stiffness in Healthy Adults

PURPOSE

This study examined the relationship between the acoustic measure relative fundamental frequency (RFF) and a kinematic estimate of laryngeal stiffness.

METHOD

Twelve healthy adults (mean age = 22.7 years, SD = 4.4; 10 women, 2 men) produced repetitions of /ifi/ while varying their vocal effort during simultaneous acoustic and video nasendoscopic recordings. RFF was determined from the last 10 voicing cycles before the voiceless obstruent (RFF offset) and the first 10 cycles of revoicing (RFF onset). A kinematic stiffness ratio was calculated for the vocal fold adductory gesture during revoicing by normalizing the maximum angular velocity by the maximum glottic angle during the voiceless obstruent.

RESULTS

A linear mixed effect model indicated that RFF offset and onset were significant predictors of the kinematic stiffness ratios. The model accounted for 52% of the variance in the kinematic data. Individual relationships between RFF and kinematic stiffness ratios varied across participants, with at least moderate negative correlations in 83% of participants for RFF offset but only 40% of participants for RFF onset.

CONCLUSIONS

RFF significantly predicted kinematic estimates of laryngeal stiffness in healthy speakers and has the potential to be a useful clinical indicator of laryngeal tension. Further research is needed in individuals with voice disorders.

Effects of Biofeedback on Control and Generalization of Nasalization in Typical Speakers

PURPOSE

The purpose of this study was to determine the effects of biofeedback on control of nasalization in individuals with typical speech.

METHOD

Forty-eight individuals with typical speech attempted to increase and decrease vowel nasalization. During training, stimuli consisted of consonant-vowel-consonant (CVC) tokens with the center vowels /a/ or /i/ in either a nasal or nonnasal phonemic context (e.g., /mim/ vs. /bib/), depending on the participant's training group. Half of the participants had access to augmentative visual feedback during training, which was based on a less-invasive acoustic, accelerometric measure of vowel nasalization-the Horii oral-nasal coupling (HONC) score. During pre- and posttraining assessments, acoustically based nasalance was also measured from the center vowels /a/, /i/, /æ/, and /u/ of CVCs in both nasal and nonnasal contexts.

RESULTS

Linear regressions indicated that both phonemic contexts (nasal or nonnasal) and the presence of augmentative visual feedback during training were significant predictors for changes in nasalance scores from pre- to posttraining.

CONCLUSIONS

Participants were able to change the nasalization of their speech following a training period with HONC biofeedback. Future work is necessary to examine the effect of such training in individuals with velopharyngeal dysfunction.

Development of an Electronic Documentation System for Voice Therapy: A New Teaching and Clinical Research Tool

Although research on the outcomes of the treatment of voice disorders is widely discussed, there is a lack of information regarding the specifics of the methods and tasks undertaken during the therapy sessions. One reason may be a lack of a clear, standardized method of documentation for the voice therapy. Therefore this article discusses the development of a new electronic documentation system for voice therapy. The goals of this documentation system are to create a user-friendly, flexible system, which implements the standard terminology and structure proposed in the recent voice therapy taxonomy (Van Stan, Roy, Awan, Stemple, & Hillman, 2015). This documentation system stores all the information from the therapy session in a local database, which is accessible for analysis within or between patients. This allows large-scale datasets to be compiled for future clinical research. This documentation system includes definitions for all terminology, and includes hierarchies, which are not required, but can be followed for additional structure. This documentation system can be used as a teaching tool, with the ability to accommodate the needs of both the novice and expert clinician.