EXPRESS: Don’t blame yourself: Conscious source monitoring modulates feedback control during speech production

Sensory feedback plays an important role in speech motor control. One of the main sources of evidence for this are studies where online auditory feedback is perturbed during ongoing speech. In motor control, it is therefore crucial to distinguish between sensory feedback and externally generated sensory events. This is called source monitoring. Previous altered feedback studies have taken non-conscious source monitoring for granted, as automatic responses to altered sensory feedback imply that the feedback changes are processed as self-caused. However, the role of conscious source monitoring is unclear. The current study investigated whether conscious source monitoring modulates responses to unexpected pitch changes in auditory feedback. During a first block, some participants spontaneously attributed the pitch shifts to themselves (self-blamers) while others attributed them to an external source (other-blamers). Before block 2, all participants were informed that the pitch shifts were experimentally induced. The self-blamers then showed a reduction in response magnitude in block 2 compared with block 1, while the other-blamers did not. This suggests that conscious source monitoring modulates responses to altered auditory feedback, such that consciously ascribing feedback to oneself leads to larger compensation responses. These results can be accounted for within the dominant comparator framework, where conscious source monitoring could modulate the gain on sensory feedback. Alternatively, the results can be naturally explained from an inferential framework, where conscious knowledge may bias the priors in a Bayesian process to determine the most likely source of a sensory event.

Exploring the Relationship Between Speech Motor Control and Phonological Processing in Children Who Stutter and Typically Developed Children

Introduction: Language processing (especially phonology) and speech motor control are disordered in stuttering. However, it is unclear how they are related based on the models of speech processing. The present study aimed to study non-word repetition, rhyme and alliteration judgment, and speech motor control and investigate their relationship in children who stutter (CWS) compared to typically developed children (TDC). Materials and Methods: Twenty-eight CWS (mean age=5.46 years) and 28 peers TDC (mean age=5.52 years) participated in this study. Phonological processing, according to the speech processing model, is divided into phonological input and output. Phonological input, phonological output, and speech motor control were assessed by rhyme and alliteration tasks, accurate phonological production during non-word repetition task, and Robbins-Klee oral speech motor protocol, respectively. The Pearson correlation coefficient, independent t-test, and Cohen’s d were used for data analysis. Results: Both non-word repetition and speech motor skills were significantly different in CWS than TDC (P<0.001). But rhyme and alliteration judgment were similar across groups (P>0.001). Phonological processing and speech motor control were not significantly correlated (P>0.001). Conclusion: Phonological processing (output), a level before articulation, and speech motor control are not correlated, but both are disordered in preschool CWS. Additionally, phonological processing (input) is similar in CWS and TDC. That is, phonological input is not affected by stuttering in CWS.

When inefficient speech-motor control affects speech comprehension: atypical electrophysiological correlates of language prediction in stuttering

It is well attested that people predict forthcoming information during language comprehension. The literature presents different proposals on how this ability could be implemented. Here, we tested the hypothesis according to which language production mechanisms have a role in such predictive processing. To this aim, we studied two electroencephalographic correlates of predictability during speech comprehension ‒ pre-target alpha‒beta (8-30 Hz) power decrease and the post-target N400 event-related potential (ERP) effect, ‒ in a population with impaired speech-motor control, i.e., adults who stutter (AWS), compared to typically fluent adults (TFA). Participants listened to sentences that could either constrain towards a target word or not, allowing or not to make predictions. We analyzed time-frequency modulations in a silent interval preceding the target and ERPs at the presentation of the target. Results showed that, compared to TFA, AWS display: i) a widespread and bilateral reduced power decrease in posterior temporal and parietal regions, and a power increase in anterior regions, especially in the left hemisphere (high vs. low constraining) and ii) a reduced N400 effect (non-predictable vs. predictable). The results suggest a reduced efficiency in generating predictions in AWS with respect to TFA. Additionally, the magnitude of the N400 effect in AWS is correlated with alpha power change in the right pre-motor and supplementary motor cortex, a key node in the dysfunctional network in stuttering. Overall, the results support the idea that processes and neural structures prominently devoted to speech planning and execution support prediction during language comprehension.

Convergence in voice fundamental frequency during synchronous speech

Joint speech behaviours where speakers produce speech in unison are found in a variety of everyday settings, and have clinical relevance as a temporary fluency-enhancing technique for people who stutter. It is currently unknown whether such synchronisation of speech timing among two speakers is also accompanied by alignment in their vocal characteristics, for example in acoustic measures such as pitch. The current study investigated this by testing whether convergence in voice fundamental frequency (F0) between speakers could be demonstrated during synchronous speech. Sixty participants across two online experiments were audio recorded whilst reading a series of sentences, first on their own, and then in synchrony with another speaker (the accompanist) in a number of between-subject conditions. Experiment 1 demonstrated significant convergence in participants’ F0 to a pre-recorded accompanist voice, in the form of both upward (high F0 accompanist condition) and downward (low and extra-low F0 accompanist conditions) changes in F0. Experiment 2 demonstrated that such convergence was not seen during a visual synchronous speech condition, in which participants spoke in synchrony with silent video recordings of the accompanist. An audiovisual condition in which participants were able to both see and hear the accompanist in pre-recorded videos did not result in greater convergence in F0 compared to synchronisation with the pre-recorded voice alone. These findings suggest the need for models of speech motor control to incorporate interactions between self- and other-speech feedback during speech production, and suggest a novel hypothesis for the mechanisms underlying the fluency-enhancing effects of synchronous speech in people who stutter.

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.

Synchronised speech and speech motor control: convergence in voice fundamental frequency during choral speech

Synchronised speech behaviours such as choral speech (speaking in unison) are found in a variety of everyday settings, and have clinical relevance as a temporary fluency-enhancing technique for people who stutter. It is currently unknown whether such synchronisation of speech timing among two speakers is also accompanied by alignment in their vocal characteristics, for example in acoustic measures such as pitch. The current study investigated this by testing whether convergence in voice fundamental frequency (F0) between speakers could be demonstrated during choral speech. Sixty participants across three online experiments were audio recorded whilst reading a series of sentences, first on their own, and then in synchrony with another speaker (the accompanist) in a number of between-subject conditions. Experiment 1 demonstrated significant convergence in participants’ F0 to a pre-recorded accompanist voice, in the form of both upward (high F0 accompanist condition) and downward (low F0 accompanist condition) changes in F0; however, upward convergence was greater than downward convergence. Experiment 2 found that downward convergent changes in F0 could not be increased by the use of an accompanist voice with an even lower F0. Experiment 3 demonstrated that such convergence was not seen during a visual choral speech condition, in which participants spoke in synchrony with silent video recordings of the accompanist. Further, convergence in F0 was enhanced for a condition where participants could both see and hear the accompanist in pre-recorded videos compared to synchronisation with the pre-recorded voice alone. These findings suggest the need for models of speech motor control to incorporate interactions between self- and other-speech feedback during speech production, and suggest a novel hypothesis for the mechanisms underlying the fluency-enhancing effects of choral speech in people who stutter.

The Role of Sensory Feedback in Developmental Stuttering: A Review

Developmental stuttering is a neurodevelopmental disorder that severely affects speech fluency. Multiple lines of evidence point to a role of sensory feedback in the disorder; this has led to a number of theories proposing different disruptions to the use of sensory feedback during speech motor control in people who stutter. The purpose of this review was to bring together evidence from studies using altered auditory feedback paradigms with people who stutter, in order to evaluate the predictions of these different theories. This review highlights converging evidence for particular patterns of differences in the responses of people who stutter to feedback perturbations. The implications for hypotheses on the nature of the disruption to sensorimotor control of speech in the disorder are discussed, with reference to neurocomputational models of speech control (predominantly, the DIVA model; Guenther et al., 2006; Tourville et al., 2008). While some consistent patterns are emerging from this evidence, it is clear that more work in this area is needed with developmental samples in particular, in order to tease apart differences related to symptom onset from those related to compensatory strategies that develop with experience of stuttering.

Changes in Intermuscular Coherence as a Function of Age and Phase of Speech Production During an Overt Reading Task

Purpose: The authors evaluated changes in intermuscular coherence (IMC) of orofacial and speech breathing muscles across phase of speech production in healthy younger and older adults. Method: Sixty adults (30 younger = M: 26.97 year; 30 older = M: 66.37 year) read aloud a list of 40 words. IMC was evaluated across phase: preparation (300 ms before speech onset), initiation (300 ms after onset), and total execution (entire word). Results: Orofacial IMC was lowest in the initiation, higher in preparation, and highest for the total execution phase. Chest wall IMC was lowest for the preparation and initiation and highest for the total execution phase. Despite age-related differences in accuracy, neuromuscular modulation for phase was similar between groups. Conclusion: These results expand our knowledge of speech motor control by demonstrating that IMC is sensitive to phase of speech planning and production.

Development and Validation of a Probe Word List to Assess Speech Motor Skills in Children

Purpose The aim of the study was to develop and validate a probe word list and scoring system to assess speech motor skills in preschool and school-age children with motor speech disorders. Method This article describes the development of a probe word list and scoring system using a modified word complexity measure and principles based on the hierarchical development of speech motor control known as the Motor Speech Hierarchy (MSH). The probe word list development accounted for factors related to word (i.e., motoric) complexity, linguistic variables, and content familiarity. The probe word list and scoring system was administered to 48 preschool and school-age children with moderate-to-severe speech motor delay at clinical centers in Ontario, Canada, and then evaluated for reliability and validity. Results One-way analyses of variance revealed that the motor complexity of the probe words increased significantly for each MSH stage, while no significant differences in the linguistic complexity were found for neighborhood density, mean biphone frequency, or log word frequency. The probe word list and scoring system yielded high reliability on measures of internal consistency and intrarater reliability. Interrater reliability indicated moderate agreement across the MSH stages, with the exception of MSH Stage V, which yielded substantial agreement. The probe word list and scoring system demonstrated high content, construct (unidimensionality, convergent validity, and discriminant validity), and criterion-related (concurrent and predictive) validity. Conclusions The probe word list and scoring system described in the current study provide a standardized method that speech-language pathologists can use in the assessment of speech motor control. It can support clinicians in identifying speech motor difficulties in preschool and school-age children, set appropriate goals, and potentially measure changes in these goals across time and/or after intervention.