Psychedelics in developmental stuttering to modulate brain functioning: a new therapeutic perspective?

Developmental stuttering (DS) is a neurodevelopmental speech-motor disorder characterized by symptoms such as blocks, repetitions, and prolongations. Persistent DS often has a significant negative impact on quality of life, and interventions for it have limited efficacy. Herein, we briefly review existing research on the neurophysiological underpinnings of DS -specifically, brain metabolic and default mode/social-cognitive networks (DMN/SCN) anomalies- arguing that psychedelic compounds might be considered and investigated (e.g., in randomized clinical trials) for treatment of DS. The neural background of DS is likely to be heterogeneous, and some contribution from genetically determinants of metabolic deficiencies in the basal ganglia and speech-motor cortical regions are thought to play a role in appearance of DS symptoms, which possibly results in a cascade of events contributing to impairments in speech-motor execution. In persistent DS, the difficulties of speech are often linked to a series of associated aspects such as social anxiety and social avoidance. In this context, the SCN and DMN (also influencing a series of fronto-parietal, somato-motor, and attentional networks) may have a role in worsening dysfluencies. Interestingly, brain metabolism and SCN/DMN connectivity can be modified by psychedelics, which have been shown to improve clinical evidence of some psychiatric conditions (e.g., depression, post-traumatic stress disorder, etc.) associated with psychological constructs such as rumination and social anxiety, which also tend to be present in persistent DS. To date, while there have been no controlled trials on the effects of psychedelics in DS, anecdotal evidence suggests that these agents may have beneficial effects on stuttering and its associated characteristics. We suggest that psychedelics warrant investigation in DS.

Stutterers' experiences on classic psychedelics: A preliminary self-report study.

Stuttering poses challenges to social, occupational, and educational aspects of life. Traditional behavioral therapies can be helpful but effects are often limited. Pharmaceutical treatments have been explored but there are no FDA-approved treatments for stuttering. Interest has grown in the potential use of classic psychedelics, including psilocybin and LSD, which have shown effectiveness in treating disorders with similar symptoms (e.g., anxiety, depression, PTSD). The potential effects of psychedelics on stuttering have not been explored. We conducted a preliminary investigation of self-identified stutterers who report their experiences taking classic psychedelics on the online messaging forum, Reddit. We qualitatively analyzed 114 publicly available posts, extracting meaningful units and assigning descriptor codes inductively. We then deductively organized responses into an established framework of psychedelics which includes behavioral, emotional, cognitive, belief-based, and social effects. These effects were subsequently grouped under organizing themes (positive, negative, neutral). Descriptive statistics revealed that the majority of users (74.0%) reported positive overall short-term effects particularly related to behavioral and emotional change (e.g., reduced stuttering and anxiety), but negative (9.6%), mixed (positive and negative; 4.8%), and neutral overall experiences (11.6%) were also reported. The results support the possibility that psychedelics may impact stuttering, but caution must be applied in their interpretation given the entirely uncontrolled research setting and potential adverse health effects of psychedelics as reported elsewhere. While these results do not encourage the use of psychedelics by stutterers, they suggest that future work could examine the impact of psychedelics on stuttering under supervised and in clinically controlled settings.

Reactive Inhibitory Control Precedes Overt Stuttering Events.

Research points to neurofunctional differences underlying fluent speech between stutterers and non-stutterers. Considerably less work has focused on processes that underlie stuttered vs. fluent speech. Additionally, most of this research has focused on speech motor processes despite contributions from cognitive processes prior to the onset of stuttered speech. We used MEG to test the hypothesis that reactive inhibitory control is triggered prior to stuttered speech. Twenty-nine stutterers completed a delayed-response task that featured a cue (prior to a go cue) signaling the imminent requirement to produce a word that was either stuttered or fluent. Consistent with our hypothesis, we observed increased beta power likely emanating from the right pre-supplementary motor area (R-preSMA)-an area implicated in reactive inhibitory control-in response to the cue preceding stuttered vs. fluent productions. Beta power differences between stuttered and fluent trials correlated with stuttering severity and participants' percentage of trials stuttered increased exponentially with beta power in the R-preSMA. Trial-by-trial beta power modulations in the R-preSMA following the cue predicted whether a trial would be stuttered or fluent. Stuttered trials were also associated with delayed speech onset suggesting an overall slowing or freezing of the speech motor system that may be a consequence of inhibitory control. Post-hoc analyses revealed that independently generated anticipated words were associated with greater beta power and more stuttering than researcher-assisted anticipated words, pointing to a relationship between self-perceived likelihood of stuttering (i.e., anticipation) and inhibitory control. This work offers a neurocognitive account of stuttering by characterizing cognitive processes that precede overt stuttering events.

Contemporary clinical conversations about stuttering: What does brain imaging research mean to clinicians?

PURPOSE: To discuss among neuroscientists and community speech-language pathologists what brain imaging research means to clinicians. METHOD: Two university neuroscientists and two speech-language pathologists in private practice discussed the matter. Written conversational turns in an exchange were limited to 100 words each. When that written dialogue was concluded, each participant provided 200 words of final reflection about the matter. RESULT: For now, neuroscience treatments are not available for clinicians to use. But sometime in the future, a critical mass of neuroscientists will likely produce such treatments. The neuroscientists expressed diverse views about the methods that might be used for that to occur. CONCLUSION: Neuroscience does have practical clinical application at present and, in a way, that does not exclude a concurrent influence of the social model of disability. As such, the current practices of clinicians are supported by basic neuroscience research.

Linguistic features of stuttering during spontaneous speech.

PURPOSE: Previous work shows that linguistic features (e.g., word length, word frequency) impact the predictability of stuttering events. Most of this work has been conducted using reading tasks. Our study examined how linguistic features impact the predictability of stuttering events during spontaneous speech. METHODS: The data were sourced from the FluencyBank database and consisted of interviews with 35 adult stutterers (27,009 words). Three logistic regression mixed models were fit as the primary analyses: one model with four features (i.e., initial phoneme, grammatical function, word length, and word position within a sentence), a second model with six features (i.e., the features from the previous model plus word frequency and neighborhood density), and a third model with nine features (i.e., the features from the previous model plus bigram frequency, word concreteness, and typical age of word acquisition). We compared our models using the Area Under the Curve statistic. RESULTS: The four-feature model revealed that initial phoneme, grammatical function, and word length were predictive of stuttering events. The six-feature model revealed that initial phoneme, word length, word frequency, and neighborhood density were predictive of stuttering events. The nine-feature model was not more predictive than the six-feature model. CONCLUSION: Linguistic features that were previously found to be predictive of stuttering during reading were predictive of stuttering during spontaneous speech. The results indicate the influence of linguistic processes on the predictability of stuttering events such that words associated with increased planning demands (e.g., longer words, low frequency words) were more likely to be stuttered.

Eliciting Stuttering in School-Age and Adolescent Stutterers in Experimental Settings.

PURPOSE: Most neural and physiological research on stuttering focuses on the fluent speech of speakers who stutter due to the difficulty associated with eliciting stuttering reliably in the laboratory. We previously introduced an approach to elicit stuttered speech in the laboratory in adults who stutter. The purpose of this study was to determine whether that approach reliably elicits stuttering in school-age children and teenagers who stutter (CWS/TWS). METHOD: Twenty-three CWS/TWS participated. A clinical interview was used to identify participant-specific anticipated and unanticipated words in CWS and TWS. Two tasks were administered: (a) a delayed word reading task in which participants read words and produced them after a 5-s delay and (b) a delayed response question task in which participants responded to examiner questions after a 5-s delay. Two CWS and eight TWS completed the reading task; six CWS and seven TWS completed the question task. Trials were coded as unambiguously fluent, ambiguous, and unambiguously stuttered. RESULTS: The method yielded, at a group level, a near-equal distribution of unambiguously stuttered and fluent utterances: 42.5% and 45.1%, respectively, in the reading task and 40.5% and 51.4%, respectively, in the question task. CONCLUSIONS: The method presented in this article elicited a comparable amount of unambiguously stuttered and fluent trials in CWS and TWS, at a group level, during two different word production tasks. The inclusion of different tasks supports the generalizability of our approach, which can be used to elicit stuttering in studies that aim to unravel the neural and physiological bases that underlie stuttered speech.

The Relationship Between Auditory-Motor Integration, Interoceptive Awareness, and Self-Reported Stuttering Severity.

Stuttering is a neurodevelopmental speech disorder associated with motor timing that differs from non-stutterers. While neurodevelopmental disorders impacted by timing are associated with compromised auditory-motor integration and interoception, the interplay between those abilities and stuttering remains unexplored. Here, we studied the relationships between speech auditory-motor synchronization (a proxy for auditory-motor integration), interoceptive awareness, and self-reported stuttering severity using remotely delivered assessments. Results indicate that in general, stutterers and non-stutterers exhibit similar auditory-motor integration and interoceptive abilities. However, while speech auditory-motor synchrony (i.e., integration) and interoceptive awareness were not related, speech synchrony was inversely related to the speaker's perception of stuttering severity as perceived by others, and interoceptive awareness was inversely related to self-reported stuttering impact. These findings support claims that stuttering is a heterogeneous, multi-faceted disorder such that uncorrelated auditory-motor integration and interoception measurements predicted different aspects of stuttering, suggesting two unrelated sources of timing differences associated with the disorder.

The effect of gap duration on the perception of fluent versus disfluent speech.

PURPOSE: Gap duration contributes to the perception of utterances as fluent or disfluent, but few studies have systematically investigated the impact of gap duration on fluency judgments. The purposes of this study were to determine how gaps impact disfluency perception, and how listener background and experience impact these judgments. METHODS: Sixty participants (20 adults who stutter [AWS], 20 speech-language pathologists [SLPs], and 20 naïve listeners) listened to four tokens of the utterance, "Buy Bobby a puppy," produced at typical speech rates. The gap duration between "Buy" and "Bobby" was systematically manipulated with gaps ranging from 23.59 ms to 325.44 ms. Participants identified stimuli as fluent or disfluent. RESULTS: The disfluency threshold - the point at which 50 % of trials were categorized as disfluent - occurred at a gap duration of 126.46 ms, across all participants and tokens. The SLPs exhibited higher disfluency thresholds than the AWS and the naïve listeners. CONCLUSION: This study determined, based on the specific set of stimuli used, when the perception of utterances tends to shift from fluent to disfluent. Group differences indicated that SLPs are less inclined to identify disfluencies in speech potentially because they aim to be less critical of speech that deviates from "typical".

Activation in Right Dorsolateral Prefrontal Cortex Underlies Stuttering Anticipation.

People who stutter learn to anticipate many of their overt stuttering events. Despite the critical role of anticipation, particularly how responses to anticipation shape stuttering behaviors, the neural bases associated with anticipation are unknown. We used a novel approach to identify anticipated and unanticipated words, which were produced by 22 adult stutterers in a delayed-response task while hemodynamic activity was measured using functional near infrared spectroscopy (fNIRS). Twenty-two control participants were included such that each individualized set of anticipated and unanticipated words was produced by one stutterer and one control participant. We conducted an analysis on the right dorsolateral prefrontal cortex (R-DLPFC) based on converging lines of evidence from the stuttering and cognitive control literatures. We also assessed connectivity between the R-DLPFC and right supramarginal gyrus (R-SMG), two key nodes of the frontoparietal network (FPN), to assess the role of cognitive control, and particularly error-likelihood monitoring, in stuttering anticipation. All analyses focused on the five-second anticipation phase preceding the go signal to produce speech. The results indicate that anticipated words are associated with elevated activation in the R-DLPFC, and that compared to non-stutterers, stutterers exhibit greater activity in the R-DLPFC, irrespective of anticipation. Further, anticipated words are associated with reduced connectivity between the R-DLPFC and R-SMG. These findings highlight the potential roles of the R-DLPFC and the greater FPN as a neural substrate of stuttering anticipation. The results also support previous accounts of error-likelihood monitoring and action-stopping in stuttering anticipation. Overall, this work offers numerous directions for future research with clinical implications for targeted neuromodulation.

Adults who stutter do not stutter during private speech.

PURPOSE: Adults who stutter tend not to stutter when they are alone. This phenomenon is difficult to study because it is difficult to know whether participants perceive that they are truly alone and not being heard or observed. This may explain the presence of stuttering during previous studies in which stutterers spoke while they were alone. We addressed this issue by developing a paradigm that elicited private speech, or overt speech meant only for the speaker. We tested the hypothesis that adults do not stutter during private speech. METHOD: Twenty-four participants were audio-/video-recorded while speaking in several conditions: 1) conversational speech; 2) reading; 3) private speech, in which deception was used to increase the probability that participants produced speech intended for only themselves; 4) private speech+, for which real-time transcription was used so that participants produced the same words as in the private speech condition but while addressing two listeners; and 5) a second conversational speech condition. RESULTS: Stuttering was not observed in more than 10,000 syllables produced during the private speech condition, except for seven possible, mild stuttering events exhibited by 3 of 24 participants. Stuttering frequency was similar for the remaining conditions. CONCLUSIONS: Adults appear not to stutter during private speech, indicating that speakers' perceptions of listeners, whether real or imagined, play a critical and likely necessary role in the manifestation of stuttering events. Future work should disentangle whether this is due to the removal of concerns about social evaluation or judgment, self-monitoring, or other communicative processes.

Speech planning and execution in children who stutter: Preliminary findings from a fNIRS investigation.

Few studies have investigated the neural mechanisms underlying speech production in children who stutter (CWS), despite the critical importance of understanding these mechanisms closer to the time of stuttering onset. The relative contributions of speech planning and execution in CWS therefore are also unknown. Using functional near-infrared spectroscopy, the current study investigated neural mechanisms of planning and execution in a small sample of 9-12 year-old CWS and controls (N = 12) by implementing two tasks that manipulated speech planning and execution loads. Planning was associated with atypical activation in bilateral inferior frontal gyrus and right supramarginal gyrus. Execution was associated with atypical activation in bilateral precentral gyrus and inferior frontal gyrus, as well as right supramarginal gyrus and superior temporal gyrus. The CWS exhibited some activation patterns that were similar to the adults who stutter (AWS) as reported in our previous study: atypical planning in frontal areas including left inferior frontal gyrus and atypical execution in fronto-temporo-parietal regions including left precentral gyrus, and right inferior frontal, superior temporal, and supramarginal gyri. However, differences also emerged. Whereas CWS and AWS both appear to exhibit atypical activation in right inferior and supramarginal gyri during execution, only CWS appear to exhibit this same pattern during planning. In addition, the CWS appear to exhibit atypical activation in left inferior frontal and right precentral gyri related to execution, whereas AWS do not. These preliminary results are discussed in the context of possible impairments in sensorimotor integration and inhibitory control for CWS.

Temperament is Linked to Avoidant Responses to Stuttering Anticipation.

PURPOSE: The purpose of the present study was to examine the degree to which certain temperament constructs predict individual differences in three types of behavioral responses to anticipation among children and adults who stutter (CWS and AWS, respectively): avoidance, physical change, and approach. METHODS: Participants included 64 CWS (9- to 17-years-old) and 54 AWS (18- to 50-years-old) who completed an online survey package including a temperament questionnaire (Early Adolescent Temperament Questionnaire-Revised for the CWS; Adult Temperament Questionnaire for the AWS) and the Stuttering Anticipation Scale. The data were analyzed separately for CWS and AWS using multivariate multiple regressions to assess how each temperament construct predicted avoidance, physical change, and approach responses to anticipation. RESULTS: CWS who reported higher levels of shyness were more likely to engage in avoidant behavioral responses when they anticipate an upcoming moment of stuttering. AWS who reported higher levels of orienting sensitivity were more likely to engage in avoidant behavioral responses when they anticipate an upcoming moment of stuttering. No temperament constructs predicted physical change or approach responses to anticipation among either age group. CONCLUSION: Specific aspects of temperament appear to be linked to the degree that CWS and AWS engage in avoidant behavioral responses to stuttering anticipation. These findings support the continued study of how individual differences impact the internal experience and outward manifestation of stuttering behaviors.

Deficit or Difference? Effects of Altered Auditory Feedback on Speech Fluency and Kinematic Variability in Adults Who Stutter.

Purpose The purpose of this study was to test whether adults who stutter (AWS) display a different range of sensitivity to delayed auditory feedback (DAF). Two experiments were conducted to assess the fluency of AWS under long-latency DAF and to test the effect of short-latency DAF on speech kinematic variability in AWS. Method In Experiment 1, 15 AWS performed a conversational speaking task under nonaltered auditory feedback and 250-ms DAF. The rates of stuttering-like disfluencies, other disfluencies, and speech errors and articulation rate were compared. In Experiment 2, 13 AWS and 15 adults who do not stutter (AWNS) read three utterances under four auditory feedback conditions: nonaltered auditory feedback, amplified auditory feedback, 25-ms DAF, and 50-ms DAF. Across-utterance kinematic variability (spatiotemporal index) and within-utterance variability (percent determinism and stability) were compared between groups. Results In Experiment 1, under 250-ms DAF, the rate of stuttering-like disfluencies and speech errors increased significantly, while articulation rate decreased significantly in AWS. In Experiment 2, AWS exhibited higher kinematic variability than AWNS across the feedback conditions. Under 25-ms DAF, the spatiotemporal index of AWS decreased significantly compared to the other feedback conditions. AWS showed lower overall percent determinism than AWNS, but their percent determinism increased under 50-ms DAF to approximate that of AWNS. Conclusions Auditory feedback manipulations can alter speech fluency and kinematic variability in AWS. Longer latency auditory feedback delays induce speech disruptions, while subtle auditory feedback manipulations potentially benefit speech motor control. Both AWS and AWNS are susceptible to auditory feedback during speech production, but AWS appear to exhibit a distinct continuum of sensitivity.

A rapid and sensitive lateral flow immunoassay (LFIA) for the detection of gluten in foods.

The gluten protein found in a variety of cereal grains is a food allergen that can elicit a spectrum of immuno-inflammatory responses in people. Consumer awareness has prompted changes in food labeling requirements, expanded gluten-free food product availability and increased demand for effective gluten testing methodologies. To meet the challenges associated with gluten testing from diverse and complex foods we developed a lateral flow immunoassay (LFIA) using a pair of novel gliadin monoclonal antibodies (MAbs). Using a visual gold reporter, we show sensitive gluten detection (150 ng/mL) from complex food substrates using a fast (<5 min) and easy testing methodology. In this report we characterize the binding properties of a cohort of newly generated gliadin monoclonal antibodies suitable for gluten detection using multiple assay formats and introduce a novel plug-n-play test strip platform with integrated test components in a single-use format.

Eliciting Stuttering in Laboratory Contexts.

Purpose The contextual variability of stuttering events makes it difficult to reliably elicit stuttered speech in laboratory settings. As a result, studies that compare stuttered versus fluent speech are difficult to conduct and, thus, are limited in the literature. The purpose of the current study is to describe a novel approach to elicit stuttering during laboratory testing. Method A semistructured clinical interview leveraging the phenomenon of stuttering anticipation was administered to 22 adults who stutter (1st visit). The interview was used to generate participant-specific anticipated and unanticipated word lists, which were used as stimuli during a 2nd visit so that the validity of the method could be tested. Results The method yielded a near-equal distribution of unambiguously stuttered and fluent utterances (43.6% and 43.5%, respectively). Moreover, 12.9% of the utterances were judged to be ambiguous, that is, not unambiguously stuttered or fluent. Conclusion This approach outperformed previous attempts to elicit stuttering during laboratory testing. It could be implemented in future studies that compare neural, physiological, or behavioral correlates of fluent versus stuttered speech.

A fNIRS Investigation of Speech Planning and Execution in Adults Who Stutter.

Our study aimed to determine the neural correlates of speech planning and execution in adults who stutter (AWS). Fifteen AWS and 15 controls (CON) completed two tasks that either manipulated speech planning or execution processing loads. Functional near-infrared spectroscopy (fNIRS) was used to measure changes in blood flow concentrations during each task, thus providing an indirect measure of neural activity. An image-based reconstruction technique was used to analyze the results and facilitate their interpretation in the context of previous functional neuroimaging studies of AWS that used positron emission tomography (PET) or functional magnetic resonance imaging (fMRI). For planning, we compared neural activity associated with high versus low planning load in AWS and CON. For execution, we compared the neural activity associated with overt versus covert naming in AWS and CON. Broadly, group level effects corroborate previous PET/fMRI findings including under-activation in left-hemisphere perisylvian speech-language networks and over-activation in right-hemisphere homologs. Increased planning load revealed atypical left-hemisphere activation in AWS, whereas increased execution load yielded atypical right fronto-temporo-parietal and bilateral motor activation in AWS. Our results add to the limited literature differentiating speech planning versus execution processes in AWS.

An exploratory factor analysis of action responses to stuttering anticipation.

PURPOSE: We previously introduced theStuttering Anticipation Scale (SAS; Jackson, E. S., Gerlach, H., Rodgers, N. H., & Zebrowski, P. M. (2018). My Client Knows That He's About to Stutter: How Can We Address Stuttering Anticipation during Therapy with Young People Who Stutter? Seminars in Speech and Language, 39, 356-370) - a non-standardized self-report measure for children, teens, and adults who stutter (CWS, TWS, AWS) that quantifies how often they engage in 25 commonly reported action responses to anticipation. The purpose of this study was to leverage the SAS to explore the factor structure of action responses to stuttering anticipation. METHODS: A total of 121 people who stutter completed the SAS online (27 CWS, 40 TWS, 54 AWS). We used exploratory factor analysis (EFA) to determine the underlying latent variables within the 25 SAS items that characterize how people who stutter respond to anticipation. RESULTS: A three-factor model was most appropriate for the data with regard to factor loadings and other model fit indices. The three factors were named: avoidance (17 items), physical change (4 items), and approach (4 items). CONCLUSION: Understanding these three types of action responses to anticipation can help guide clinical decision-making by providing a novel framework for clinicians and their clients who stutter to discuss how the client tends to respond to anticipation, and explore ways to facilitate productive responses to anticipation.

My Client Knows That He's About to Stutter: How Can We Address Stuttering Anticipation during Therapy with Young People Who Stutter?

Stuttering anticipation is endorsed by many people who stutter as a core aspect of the stuttering experience. Anticipation is primarily a covert phenomenon and people who stutter respond to anticipation in a variety of ways. At the same time as anticipation occurs and develops internally, for many individuals the "knowing" or "feeling" that they are about to stutter is a primary contributor to the chronicity of the disorder. In this article, we offer a roadmap for both understanding the phenomenon of anticipation and its relevance to stuttering development. We introduce the Stuttering Anticipation Scale (SAS)-a 25-item clinical tool that can be used to explore a client's internal experience of anticipation to drive goal development and clinical decision making. We ground this discussion in a hypothetical case study of "Ryan," a 14-year-old who stutters, to demonstrate how clinicians might use the SAS to address anticipation in therapy with young people who stutter.

The Impact of Social-Cognitive Stress on Speech Variability, Determinism, and Stability in Adults Who Do and Do Not Stutter.

Purpose: This study examined the impact of social-cognitive stress on sentence-level speech variability, determinism, and stability in adults who stutter (AWS) and adults who do not stutter (AWNS). We demonstrated that complementing the spatiotemporal index (STI) with recurrence quantification analysis (RQA) provides a novel approach to both assessing and interpreting speech variability in stuttering. Method: Twenty AWS and 21 AWNS repeated sentences in audience and nonaudience conditions while their lip movements were tracked. Across-sentence variability was assessed via the STI; within-sentence determinism and stability were assessed via RQA. Results: Compared with the AWNS, the AWS produced speech that was more variable across sentences and more deterministic and stable within sentences. Audience presence contributed to greater within-sentence determinism and stability in the AWS. A subset of AWS who were more susceptible to experiencing anxiety exhibited reduced across-sentence variability in the audience condition compared with the nonaudience condition. Conclusions: This study extends the assessment of speech variability in AWS and AWNS into the social-cognitive domain and demonstrates that the characterization of speech within sentences using RQA is complementary to the across-sentence STI measure. AWS seem to adopt a more restrictive, less flexible speaking approach in response to social-cognitive stress, which is presumably a strategy for maintaining observably fluent speech.

Recurrence Quantification Analysis of Sentence-Level Speech Kinematics.

Purpose: Current approaches to assessing sentence-level speech variability rely on measures that quantify variability across utterances and use normalization procedures that alter raw trajectory data. The current work tests the feasibility of a less restrictive nonlinear approach-recurrence quantification analysis (RQA)-via a procedural example and subsequent analysis of kinematic data. Method: To test the feasibility of RQA, lip aperture (i.e., the Euclidean distance between lip-tracking sensors) was recorded for 21 typically developing adult speakers during production of a simple utterance. The utterance was produced in isolation and in carrier structures differing just in length or in length and complexity. Four RQA indices were calculated: percent recurrence (%REC), percent determinism (%DET), stability (MAXLINE), and stationarity (TREND). Results: Percent determinism (%DET) decreased only for the most linguistically complex sentence; MAXLINE decreased as a function of linguistic complexity but increased for the longer-only sentence; TREND decreased as a function of both length and linguistic complexity. Conclusions: This research note demonstrates the feasibility of using RQA as a tool to compare speech variability across speakers and groups. RQA offers promise as a technique to assess effects of potential stressors (e.g., linguistic or cognitive factors) on the speech production system.