From planning to articulation in speech production: what differentiates a person who stutters from a person who does not stutter?

Erasmus clinical model of the onset and development of stuttering 2.0

A clinical, evidence-based model to inform clients and their parents about the nature of stuttering is indispensable for the field. In this paper, we propose the Erasmus Clinical Model of Stuttering 2.0 for children who stutter and their parents, and adult clients. It provides an up-to-date, clinical model summary of current insights into the genetic, neurological, motoric, linguistic, sensory, temperamental, psychological and social factors (be it causal, eliciting, or maintaining) related to stuttering. First a review is presented of current insights in these factors, and of six scientific theories or models that have inspired the development of our current clinical model. Following this, we will propose the model, which has proven to be useful in clinical practice. The proposed Erasmus Clinical Model of Stuttering visualizes the onset and course of stuttering, and includes scales for stuttering severity and impact, to be completed by the (parent of) the person who stutters. The pathway of the model towards stuttering onset is based on predisposing and mediating factors. In most children with an onset of stuttering, stuttering is transient, but if stuttering continues, its severity and impact vary widely. The model includes the circle of Engel (1977), which visualizes unique interactions of relevant biological, psychological, and social factors that determine the speaker's experience of stuttering severity and its impact. Discussing these factors and their interaction with an individual client can feed into therapeutic targets. The model is supplemented by a lifeline casus.

Reactions and responses to anticipation of stuttering and how they contribute to stuttered speech that listeners perceive as fluent - An opinion paper

The experience of stuttering is wide ranging and includes a variety of perceived and unperceived behaviors and experiences. One of those experiences is anticipation of stuttering. While anticipation of stuttering is commonly discussed in terms of being a prediction of an upcoming event, it has also been equated to an internal realization of stuttering - which is the conceptualization applied here. The aim of this paper is to impress upon the reader that anticipated moments of stuttering (whether at a conscious or subconscious level) must be met with an adaptive reaction or response (which may also occur consciously or subconsciously). While these adaptive reactions and responses may differ based on whether they promote positive or negative communicative behaviors, they still represent adaptations by the speaker. Among the broad category of reactions and responses to anticipation of stuttering are motoric adaptations to speech, which include characteristic stuttering behaviors and other adaptations that may contribute to speech that is perceived by listeners as fluent. An outcome of this conceptualization is, even when adaptations result in listener perceived fluency, the speech of the person who stutters is still controlled by stuttering - meaning that some observable or unobservable adaptation is required. It is critical that speech-language pathologists recognize that the behaviors of people who stutter may reflect reactions and responses to an internal realization of stuttering and observable and unobservable reactions and responses must be considered in both assessments and interventions.

Speech Movement Variability in People Who Stutter: A Vocal Tract Magnetic Resonance Imaging Study

Purpose People who stutter (PWS) have more unstable speech motor systems than people who are typically fluent (PWTF). Here, we used real-time magnetic resonance imaging (MRI) of the vocal tract to assess variability and duration of movements of different articulators in PWS and PWTF during fluent speech production. Method The vocal tracts of 28 adults with moderate to severe stuttering and 20 PWTF were scanned using MRI while repeating simple and complex pseudowords. Midsagittal images of the vocal tract from lips to larynx were reconstructed at 33.3 frames per second. For each participant, we measured the variability and duration of movements across multiple repetitions of the pseudowords in three selected articulators: the lips, tongue body, and velum. Results PWS showed significantly greater speech movement variability than PWTF during fluent repetitions of pseudowords. The group difference was most evident for measurements of lip aperture using these stimuli, as reported previously, but here, we report that movements of the tongue body and velum were also affected during the same utterances. Variability was not affected by phonological complexity. Speech movement variability was unrelated to stuttering severity within the PWS group. PWS also showed longer speech movement durations relative to PWTF for fluent repetitions of multisyllabic pseudowords, and this group difference was even more evident as complexity increased. Conclusions Using real-time MRI of the vocal tract, we found that PWS produced more variable movements than PWTF even during fluent productions of simple pseudowords. PWS also took longer to produce multisyllabic words relative to PWTF, particularly when words were more complex. This indicates general, trait-level differences in the control of the articulators between PWS and PWTF. Supplemental Material https://doi.org/10.23641/asha.14782092.

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.

An articulatory study of differences and similarities between stuttered disfluencies and non-pathological disfluencies

While stuttering-like disfluencies have long interested researchers, little is known about their articulatory realisation. Yet, such a description seems crucial in order to better understand the differences between stuttering-like and other disfluencies, and their underlying motor mechanisms. Hence, we aimed to compare the articulatory supraglottic activity in stuttered disfluencies with non-pathological disfluencies by using Electromagnetic Articulography (EMA) data. To achieve this comparison, two criteria were used for the description of articulatory activity during the disfluency. The first focused on the characterisation of the movements observable during the disfluency. This criterion gives an indication of the presence or absence of articulatory movement as well as interarticulator coupling. The second criterion provided information on the retention and anticipation of the sound preceding and following the disfluency. In order to strengthen our analysis, both criteria were examined using two complementary methodologies. The first was an expert-based analysis, while the second used a set of metrics based on velocity and acceleration. These analyses were conducted independently, and the final results of our study corresponded to the conclusions of the comparison of both methodology results. The results we obtained show that stuttered disfluencies and non-pathological disfluencies do have common characteristics. However, stuttered disfluencies and non-pathological disfluencies produced by Persons Who Stutter (PWS) present some particularities, mainly in terms of retention and anticipation, and the presence of spasmodic movements. Results are discussed in the light of different models of stuttering.

Inhibitory Control of Lexical Selection in Adults who Stutter

PURPOSE

Based on previous evidence that lexical selection may operate differently in adults who stutter (AWS) versus typically-fluent adults (TFA), and that atypical attentional processing may be a contributing factor, the purpose of this study was to investigate inhibitory control of lexical selection in AWS.

METHOD

12 AWS and 12 TFA completed two tasks. One was a picture naming task featuring High and Low Agreement object naming. Naming accuracy and reaction times (RT), and event-related potentials (ERPs) time-locked to picture onset, were recorded. Second was a flanker task featuring Congruent and Incongruent arrow arrays. Push-button accuracy and RTs, and ERPs time-locked to arrow array onset, were recorded.

RESULTS

Low Agreement pictures were named less accurately and slower than High Agreement pictures in both Groups. The magnitude of the Agreement effect on naming RTs was larger in AWS versus TFA. Delta-plot analysis revealed that the Agreement effect was positively correlated with individual differences in inhibition in TFA but not in AWS. Moreover, Low Agreement pictures elicited negative-going ERP activity relative to High Agreement pictures in both Groups. However, the scalp topography of this effect was markedly reduced in AWS versus TFA. For the Flanker task, Congruency affected push-button accuracy and RTs, and N2 amplitudes, similarly between groups.

CONCLUSIONS

Results point to a selective deficit in inhibitory control of lexical selection in AWS. Potential pathways between diminished inhibitory control of lexical selection, speech motor control and stuttering are discussed.

Speaking-related changes in cortical functional connectivity associated with assisted and spontaneous recovery from developmental stuttering

We previously reported speaking-related activity changes associated with assisted recovery induced by a fluency shaping therapy program and unassisted recovery from developmental stuttering (Kell et al., Brain 2009). While assisted recovery re-lateralized activity to the left hemisphere, unassisted recovery was specifically associated with the activation of the left BA 47/12 in the lateral orbitofrontal cortex. These findings suggested plastic changes in speaking-related functional connectivity between left hemispheric speech network nodes. We reanalyzed these data involving 13 stuttering men before and after fluency shaping, 13 men who recovered spontaneously from their stuttering, and 13 male control participants, and examined functional connectivity during overt vs. covert reading by means of psychophysiological interactions computed across left cortical regions involved in articulation control. Persistent stuttering was associated with reduced auditory-motor coupling and enhanced integration of somatosensory feedback between the supramarginal gyrus and the prefrontal cortex. Assisted recovery reduced this hyper-connectivity and increased functional connectivity between the articulatory motor cortex and the auditory feedback processing anterior superior temporal gyrus. In spontaneous recovery, both auditory-motor coupling and integration of somatosensory feedback were normalized. In addition, activity in the left orbitofrontal cortex and superior cerebellum appeared uncoupled from the rest of the speech production network. These data suggest that therapy and spontaneous recovery normalizes the left hemispheric speaking-related activity via an improvement of auditory-motor mapping. By contrast, long-lasting unassisted recovery from stuttering is additionally supported by a functional isolation of the superior cerebellum from the rest of the speech production network, through the pivotal left BA 47/12.

The Influence of Executive Functions on Phonemic Processing in Children Who Do and Do Not Stutter

PURPOSE

The aim of the present study was to investigate dual-task performance in children who stutter (CWS) and those who do not to investigate if the groups differed in the ability to attend and allocate cognitive resources effectively during task performance.

METHOD

Participants were 24 children (12 CWS) in both groups matched for age and sex. For the primary task, participants performed a phoneme monitoring in a picture-written word interference task. For the secondary task, participants made pitch judgments on tones presented at varying (short, long) stimulus onset asynchrony (SOA) from the onset of the picture.

RESULTS

The CWS were comparable to the children who do not stutter in performing the monitoring task although the SOA-based performance differences in this task were more variable in the CWS. The CWS were also significantly slower in making tone decisions at the short SOA and showed a trend for making more errors in this task.

CONCLUSIONS

The findings are interpreted to suggest higher dual-task cost effects in CWS. A potential explanation for this finding requiring further testing and confirmation is that the CWS show reduced efficiency in attending to the tone stimuli while simultaneously prioritizing attention to the phoneme-monitoring task.

Motor practice effects and sensorimotor integration in adults who stutter: Evidence from visuomotor tracking performance

PURPOSE

The purpose of this study was to utilize a visuomotor tracking task, with both the jaw and hand, to add to the literature regarding non-speech motor practice and sensorimotor integration (outside of auditory-motor integration domain) in adults who do (PWS) and do not (PWNS) stutter.

METHOD

Participants were 15 PWS (14 males, mean age = 27.0) and 15 PWNS (14 males, mean age = 27.2). Participants tracked both predictable and unpredictable moving targets separately with their jaw and their dominant hand, and accuracy was assessed by calculating phase and amplitude difference between the participant and the target. Motor practice effect was examined by comparing group performance over consecutive tracking trials of predictable conditions as well as within the first trial of same conditions.

RESULTS

Results showed that compared to PWNS, PWS were not significantly different in matching either the phase (timing) or the amplitude of the target in both jaw and hand tracking of predictable and unpredictable targets. Further, there were no significant between-group differences in motor practice effects for either jaw or hand tracking. Both groups showed improved tracking accuracy within and between the trials.

CONCLUSION

Our findings revealed no statistically significant differences in non-speech motor practice effects and integration of sensorimotor feedback between PWS and PWNS, at least in the context of the visuomotor tracking tasks employed in the study. In general, both talker groups exhibited practice effects (i.e., increased accuracy over time) within and between tracking trials during both jaw and hand tracking. Implications for these results are discussed.

EDUCATIONAL OBJECTIVES

The reader will be able to: (a) describe the importance of motor learning and sensory-motor integration for speech, (b) summarize past research on PWS's performance during speech and nonspeech motor tasks, and (c) describe the relation between different aspects of speech and non-speech motor control and stuttering.

Responses of adults who stutter to the anticipation of stuttering

PURPOSE

Many people who stutter experience the phenomenon of anticipation-the sense that stuttering will occur before it is physically and overtly realized. A systematic investigation of how people who stutter respond to anticipation has not been previously reported. The purposes of this study were to provide self-report evidence of what people do in response to anticipation of stuttering and to determine the extent to which this anticipation occurs.

METHODS

Thirty adults who stutter indicated on a Likert rating scale the extent to which they anticipate stuttering and answered three open-ended (written) questions regarding how they respond to anticipation.

RESULTS

All participants reported experiencing anticipation at least "sometimes," and 77% of the participants reported experiencing anticipation "often" or "always." The extent to which participants reported experiencing anticipation was not related to stuttering severity, impact, or treatment history. Analysis of written responses revealed 24 major categories, which were heuristically divided into action or non-action responses. Categories representing avoidance and self-management strategies were further divided into 14 and 19 subcategories, respectively. Participants were just as likely to view anticipation as helpful as they were to view it as harmful.

CONCLUSION

Findings demonstrate that most, if not all, adults who stutter experience anticipation, and the majority of adults who stutter report doing so at least often. Adults who stutter respond to this anticipation by altering the speech production process in various ways. Results highlight the importance of the role that anticipation plays in how stuttering behaviors manifest themselves.

EDUCATIONAL OBJECTIVES

The reader will be able to: (a) summarize existing literature on the anticipation of stuttering; (b) describe the role and extent of anticipation of stuttering in adults; (c) describe the various ways that adults who stutter respond to anticipation; (d) describe the importance of measuring anticipation in clinical and research domains.

A review of brain circuitries involved in stuttering

Stuttering has been the subject of much research, nevertheless its etiology remains incompletely understood. This article presents a critical review of the literature on stuttering, with particular reference to the role of the basal ganglia (BG). Neuroimaging and lesion studies of developmental and acquired stuttering, as well as pharmacological and genetic studies are discussed. Evidence of structural and functional changes in the BG in those who stutter indicates that this motor speech disorder is due, at least in part, to abnormal BG cues for the initiation and termination of articulatory movements. Studies discussed provide evidence of a dysfunctional hyperdopaminergic state of the thalamocortical pathways underlying speech motor control in stuttering. Evidence that stuttering can improve, worsen or recur following deep brain stimulation for other indications is presented in order to emphasize the role of BG in stuttering. Further research is needed to fully elucidate the pathophysiology of this speech disorder, which is associated with significant social isolation.

Stuttering as a trait or state - an ALE meta-analysis of neuroimaging studies

Stuttering is a speech disorder characterised by repetitions, prolongations and blocks that disrupt the forward movement of speech. An earlier meta-analysis of brain imaging studies of stuttering (Brown et al., 2005) revealed a general trend towards rightward lateralization of brain activations and hyperactivity in the larynx motor cortex bilaterally. The present study sought not only to update that meta-analysis with recent work but to introduce an important distinction not present in the first study, namely the difference between 'trait' and 'state' stuttering. The analysis of trait stuttering compares people who stutter (PWS) with people who do not stutter when behaviour is controlled for, i.e., when speech is fluent in both groups. In contrast, the analysis of state stuttering examines PWS during episodes of stuttered speech compared with episodes of fluent speech. Seventeen studies were analysed using activation likelihood estimation. Trait stuttering was characterised by the well-known rightward shift in lateralization for language and speech areas. State stuttering revealed a more diverse pattern. Abnormal activation of larynx and lip motor cortex was common to the two analyses. State stuttering was associated with overactivation in the right hemisphere larynx and lip motor cortex. Trait stuttering was associated with overactivation of lip motor cortex in the right hemisphere but underactivation of larynx motor cortex in the left hemisphere. These results support a large literature highlighting laryngeal and lip involvement in the symptomatology of stuttering, and disambiguate two possible sources of activation in neuroimaging studies of persistent developmental stuttering.

Practice and retention of nonwords in adults who stutter

PURPOSE

We investigated short-term practice and retention of nonwords in 10 adults who stutter (Mean age=30.7 years, SD=15.1) and age and sex-matched 10 control participants (Mean age=30.8 years, SD=14.9).

METHODS

Participants were required to repeat nonwords varying in length (3, 4, and 6 syllables), phonotactic constraint (PC vs. NPC, on 3-syllable nonwords only), and complexity (simple, complex). They were tested twice with 1h gap between sessions.

RESULTS

Logistic mixed model of speech accuracy revealed that the AWS showed a significantly lower probability of correct responses with increasing length and complexity. Analysis of speech kinematics revealed practice effects within Session 1 in AWS seen as a reduction in movement variability for the 3-syllable nonwords; the control group was performing at ceiling at this length. For the 4-syllable nonwords, the control group showed a significant reduction in movement variability with practice, and retained this reduction in Session 2, while the AWS group did not show practice or retention. Group differences were not evident at the 6-syllable level.

CONCLUSIONS

Group differences in speech accuracy suggest differences in phonemic encoding and/or speech motor processes. Group differences in changes in movement variability within and between sessions suggest reduced practice and retention in AWS. Relevance of the combined use of both behavioral and kinematic measures to interpret the nature of the skill acquisition deficit in persons who stutter is discussed.

EDUCATIONAL OBJECTIVES

At the end of this activity the reader will be able to: (a) summarize the process of skill acquisition; (b) discuss the literature on skill acquisition deficits in adults who stutter, (c) summarize the differences between AWS and control participants in speech accuracy and speech kinematics with short-term practice and retention of nonwords, (d) discuss potential research directions in the area of skill acquisition in AWS.

The impact of threat and cognitive stress on speech motor control in people who stutter

PURPOSE

In the present study, an Emotional Stroop and Classical Stroop task were used to separate the effect of threat content and cognitive stress from the phonetic features of words on motor preparation and execution processes.

METHOD

A group of 10 people who stutter (PWS) and 10 matched people who do not stutter (PNS) repeated colour names for threat content words and neutral words, as well as for traditional Stroop stimuli. Data collection included speech acoustics and movement data from upper lip and lower lip using 3D EMA.

RESULTS

PWS in both tasks were slower to respond and showed smaller upper lip movement ranges than PNS. For the Emotional Stroop task only, PWS were found to show larger inter-lip phase differences compared to PNS. General threat words were executed with faster lower lip movements (larger range and shorter duration) in both groups, but only PWS showed a change in upper lip movements. For stutter specific threat words, both groups showed a more variable lip coordination pattern, but only PWS showed a delay in reaction time compared to neutral words. Individual stuttered words showed no effects. Both groups showed a classical Stroop interference effect in reaction time but no changes in motor variables.

CONCLUSION

This study shows differential motor responses in PWS compared to controls for specific threat words. Cognitive stress was not found to affect stuttering individuals differently than controls or that its impact spreads to motor execution processes.

EDUCATIONAL OBJECTIVES

After reading this article, the reader will be able to: (1) discuss the importance of understanding how threat content influences speech motor control in people who stutter and non-stuttering speakers; (2) discuss the need to use tasks like the Emotional Stroop and Regular Stroop to separate phonetic (word-bound) based impact on fluency from other factors in people who stutter; and (3) describe the role of anxiety and cognitive stress on speech motor processes.

Anxiety and speaking in people who stutter: an investigation using the emotional Stroop task

People with anxiety disorders show an attentional bias towards threat or negative emotion words. This exploratory study examined whether people who stutter (PWS), who can be anxious when speaking, show similar bias and whether reactions to threat words also influence speech motor planning and execution. Comparisons were made between 31 PWS and 31 fluent controls in a modified emotional Stroop task where, depending on a visual cue, participants named the colour of threat and neutral words at either a normal or fast articulation rate. In a manual version of the same task participants pressed the corresponding colour button with either a long or short duration. PWS but not controls were slower to respond to threat words than neutral words, however, this emotionality effect was only evident for verbal responding. Emotionality did not interact with speech rate, but the size of the emotionality effect among PWS did correlate with frequency of stuttering. Results suggest PWS show an attentional bias to threat words similar to that found in people with anxiety disorder. In addition, this bias appears to be contingent on engaging the speech production system as a response modality. No evidence was found to indicate that emotional reactivity during the Stroop task constrains or destabilises, perhaps via arousal mechanisms, speech motor adjustment or execution for PWS.

EDUCATIONAL OBJECTIVES

The reader will be able to: (1) explain the importance of cognitive aspects of anxiety, such as attentional biases, in the possible cause and/or maintenance of anxiety in people who stutter, (2) explain how the emotional Stroop task can be used as a measure of attentional bias to threat information, and (3) evaluate the findings with respect to the relationship between attentional bias to threat information and speech production in people who stutter.

Phonetic complexity and stuttering in Arabic

The current study investigated whether phonetic complexity affected stuttering rate in Jordanian Arabic speakers. Speakers were assigned to three age groups (6-11, 12-17 and 18+ years). An Arabic index of phonetic complexity (AIPC) was developed. Each word was given a score based on the number of complex phonetic properties out of a total of nine that it contained in the AIPC. The results showed that stuttering on function words for Jordanian Arabic did not correlate significantly with the AIPC score for any age group. The AIPC scores of content and function-content words correlated positively with stuttering rate for the 6-11 age group alone with the function-content words affecting fluency more severely than did the content words. The AIPC scores of stuttered function, content and stuttered function-content words were higher than those of fluent words. The non-stuttered words had lower AIPC scores than the stuttered corresponding classes. This showed that the higher the AIPC score on stuttered words, the greater the chance for these word categories to be stuttered. The AIPC factors that most affected fluency in Jordanian Arabic were place of articulation, manner of articulation, word length, word shape and consonant length. We conclude that Arabic is similar to other languages with regard to the loci of stuttering, their phonetic complexity and AIPC factors affecting stuttering most. The correlation between phonetic complexity and the order of the AIPC factors are different between Arabic and other languages.

Accuracy of perceptual and acoustic methods for the detection of inspiratory loci in spontaneous speech

The present study investigates the accuracy of perceptually and acoustically determined inspiratory loci in spontaneous speech for the purpose of identifying breath groups. Sixteen participants were asked to talk about simple topics in daily life at a comfortable speaking rate and loudness while connected to a pneumotach and audio microphone. The locations of inspiratory loci were determined on the basis of the aerodynamic signal, which served as a reference for loci identified perceptually and acoustically. Signal detection theory was used to evaluate the accuracy of the methods. The results showed that the greatest accuracy in pause detection was achieved (1) perceptually, on the basis of agreement between at least two of three judges, and (2) acoustically, using a pause duration threshold of 300 ms. In general, the perceptually based method was more accurate than was the acoustically based method. Inconsistencies among perceptually determined, acoustically determined, and aerodynamically determined inspiratory loci for spontaneous speech should be weighed in selecting a method of breath group determination.

Influences of sentence length and syntactic complexity on the speech motor control of children who stutter

PURPOSE

To investigate the potential effects of increased sentence length and syntactic complexity on the speech motor control of children who stutter (CWS).

METHOD

Participants repeated sentences of varied length and syntactic complexity. Kinematic measures of articulatory coordination variability and movement duration during perceptually fluent speech were analyzed for 16 CWS and 16 typically developing children (CTD) between 4 and 6 years of age. Behavioral data from a larger pool of children were also examined.

RESULTS

For both groups, articulatory coordination variability increased with sentence length. For syntactically simple sentences, CWS had higher coordination variability than CTD. There was no group difference in coordination variability for complex sentences. Coordination variability increased significantly with complexity for CTD, whereas that of CWS remained at the high level demonstrated for simple sentences. There was a trend for higher overall coordination variability in CWS compared with CTD. For both groups, movement duration was greater for syntactically complex, as compared with simple, sentences.

CONCLUSIONS

Results indicate more variable speech motor coordination during fluent speech production in many CWS as compared with CTD. Disproportionate effects of length and complexity on coordination variability and duration were not found for CWS. Considerable individual differences in performance were observed.

Early-stage chunking of finger tapping sequences by persons who stutter and fluent speakers

This research note explored the hypothesis that chunking differences underlie the slow finger-tap sequencing performance reported in the literature for persons who stutter (PWS) relative to fluent speakers (PNS). Early-stage chunking was defined as an immediate and spontaneous tendency to organize a long sequence into pauses, for motor planning, and chunks of fluent motor performance. A previously published study in which 12 PWS and 12 matched PNS practised a 10-item finger tapping sequence 30 times was examined. Both groups significantly decreased the duration of between-chunk intervals (BCIs) and within-chunk intervals (WCIs) over practice. PNS had significantly shorter WCIs relative to PWS, but minimal differences between groups were found for the number of, or duration of, BCI. Results imply that sequencing differences found between PNS and PWS may be due to differences in automatizing movements within chunks or retrieving chunks from memory rather than chunking per se.

Speech sequence skill learning in adults who stutter

The present study compared the ability of 12 people who stutter (PWS) and 12 people who do not stutter (PNS) to consolidate a novel sequential speech task. Participants practiced 100 repetitions of a single, monosyllabic, nonsense word sequence during an initial practice session and returned 24-h later to perform an additional 50 repetitions. Results showed significantly slower sequence durations in the PWS compared to PNS following extensive practice and consolidation. However, the hypothesis that poor performance gains in PWS compared to PNS during practice would be maintained following a 24-h consolidation period was not supported. Further descriptive analysis revealed large within group differences in PWS which to some extent were attributed to a subgroup of PWS who failed to show any improvements in performance following practice or consolidation. The results and the possible presence of subgroups of PWS are discussed with regard to their limitations in motor learning abilities.

EDUCATIONAL OBJECTIVES

The reader will be able to (1) explain the difference between practice and learning, (2) define consolidation and explain the importance of measuring performance following a consolidation period, (3) understand past research on PWS' performance during both speech and nonspeech motor tasks, and (4) explain why individual differences in practice effects and learning may have important implications for client variability in treatment outcome.

Overreliance on auditory feedback may lead to sound/syllable repetitions: simulations of stuttering and fluency-inducing conditions with a neural model of speech production

This paper investigates the hypothesis that stuttering may result in part from impaired readout of feedforward control of speech, which forces persons who stutter (PWS) to produce speech with a motor strategy that is weighted too much toward auditory feedback control. Over-reliance on feedback control leads to production errors which if they grow large enough, can cause the motor system to "reset" and repeat the current syllable. This hypothesis is investigated using computer simulations of a "neurally impaired" version of the DIVA model, a neural network model of speech acquisition and production. The model's outputs are compared to published acoustic data from PWS' fluent speech, and to combined acoustic and articulatory movement data collected from the dysfluent speech of one PWS. The simulations mimic the errors observed in the PWS subject's speech, as well as the repairs of these errors. Additional simulations were able to account for enhancements of fluency gained by slowed/prolonged speech and masking noise. Together these results support the hypothesis that many dysfluencies in stuttering are due to a bias away from feedforward control and toward feedback control.

EDUCATIONAL OBJECTIVES

The reader will be able to (a) describe the contribution of auditory feedback control and feedforward control to normal and stuttered speech production, (b) summarize the neural modeling approach to speech production and its application to stuttering, and (c) explain how the DIVA model accounts for enhancements of fluency gained by slowed/prolonged speech and masking noise.

Sensory feedback dependence hypothesis in persons who stutter

The present study investigated the role of sensory feedback (auditory, proprioception, and tactile) at the intra- and inter-gestural levels of speech motor coordination in normal and fast speech rate conditions in two groups: (1) persons who stutter (PWS) and (2) those who do not (PNS). Feedback perturbations were carried out with the use of masking noise (auditory), tendon vibration (proprioception), and nonwords that differed in the amount of required tactile lip contact (/api/+tactile and /awi/-tactile). Comparisons were also made between jaw-free and jaw-immobilized (with a bite-block) task conditions. It was hypothesized that if PWS depend more strongly on sensory feedback control during speech production, they would show an increase in variability of movement coordination in the combined presence of fast speech rates and feedback perturbations, in particular, when jaw motions are blocked and adaptations in the other articulators are required to achieve the task goals. Significant feedback perturbation effects were found for both groups, but the only significant between-group effect was found at fast speech rates in the jaw-free condition, showing that control speakers were more perturbed at the intra-gestural level of coordination than PWS when simultaneous (auditory, proprioceptive, and tactile) perturbations were present. The findings do not provide support for either the feedback dependency or the sensory deficit hypotheses described in the literature to explain movement characteristics found in fluent speech production of PWS.

Speech skill learning of persons who stutter and fluent speakers under single and dual task conditions

Two studies compared the accuracy and efficiency of initiating oral reading of nonsense syllables by persons who stutter (PWS) and fluent speakers (PNS) over practise. Findings of Study One, comparing 12 PWS and 12 PNS, replicated previous findings of slow speech sequence initiation over practise by PWS relative to PNS. In Study Two, nine PWS and eight PNS practised reading syllable sequences under single, and then dual task conditions in which a colour recognition distracter task was introduced. The speech sequences of PWS were initiated significantly slower than those of PNS. Significant GroupxCondition interactions for reaction time and accuracy were interpreted to suggest that PNS, but not PWS, demonstrated the ability to switch between an attention-demanding movement strategy under dual task conditions and a relatively automatic (little attention required) movement strategy after practise under single task conditions.

Speeded verbal responding in adults who stutter: are there deficits in linguistic encoding?

Linguistic encoding deficits in people who stutter (PWS, n=18) were investigated using auditory priming during picture naming and word vs. non-word comparisons during choice and simple verbal reaction time (RT) tasks. During picture naming, PWS did not differ significantly from normally fluent speakers (n=18) in the magnitude of inhibition of RT from semantically related primes and the magnitude of facilitation from phonologically related primes. PWS also did not differ from controls in the degree to which words were faster than non-words during choice RT, although PWS were slower overall than controls. Simple RT showed no difference between groups, or between words and non-words, suggesting differences in speech initiation time do not explain the choice RT results. The findings are consistent with PWS not being deficient in the time course of lexical activation and selection, phonological encoding, and phonetic encoding. Potential deficits underlying slow choice RTs outside of linguistic encoding are discussed.

EDUCATIONAL OBJECTIVES

The reader will be able to (1) describe possible relationships between linguistic encoding processes and speech motor control difficulties in people who stutter; (2) explain the role of lexical priming tasks during speech production in evaluating the efficiency of linguistic encoding; (3) describe the different levels of processing that may be involved in slow verbal responding by people who stutter, and identify which levels could be involved based on the findings of the present study.

Bite-block perturbation in people who stutter: immediate compensatory and delayed adaptive processes

This exploratory study investigated sensory-motor mechanisms in five people who stutter (PWS) and five people who do not (PNS). Lip kinematic and coordination data were recorded as they produced bi-syllabic nonwords at two rates (normal and fast) in three conditions (jaw-free, immediately after insertion of a bite-block, and after a 10-min accommodation period). At normal speech rates, effects of bite-blocks on lip kinematics were similar for both PWS and PNS speakers showing larger amplitudes, peak velocities, shorter durations and more stable movement cycle patterns. However, at fast speech rates upper lip responses of PWS exhibited larger amplitudes and peak velocities. At both speech rates, the presence of a bite-block changed movement coordination patterns only for PNS. However, at fast speech rates bite-blocks decreased variability of coordination patterns for both groups. No adaptive changes in movement stability were found for either group, but a practice-related increase in lower lip peak velocity was found at normal speech rates. These findings indicate that bite-block perturbation did not exacerbate any hypothesized limitation or difficulty in controlling individual articulatory movements or their coordination in PWS. The results also support the position that specific motor control strategies are used by PWS as compared to PNS to compensate for bite-block perturbations under increased speech rate demands.

LEARNING OUTCOMES

The reader will be able to: (1) distinguish between compensatory and adaptive responses to bite-block perturbation; (2) explain the measurement of articulatory stability; (3) summarize the potential role of motor control strategies in people who stutter; and (4) discuss the assumptions of the motor skills approach to stuttering.

Investigating speech motor practice and learning in people who stutter

In this exploratory study, we investigated whether or not people who stutter (PWS) show motor practice and learning changes similar to those of people who do not stutter (PNS). To this end, five PWS and five PNS repeated a set of non-words at two different rates (normal and fast) across three test sessions (T1, T2 on the same day and T3 on a separate day, at least 1 week apart). The results indicated that PWS and PNS may resemble each other on a number of performance variables (such as movement amplitude and duration), but they differ in terms of practice and learning on variables that relate to movement stability and strength of coordination patterns. These findings are interpreted in support of recent claims about speech motor skill limitations in PWS.

EDUCATIONAL OBJECTIVES

The reader will be able to: (1) define oral articulatory changes associated with motor practice and learning and their measurement; (2) summarize findings from previous studies examining motor practice and learning in PWS; and (3) discuss hypotheses that could account for the present findings that suggest PWS and PNS differ in their speech motor learning abilities.

Sequence skill learning in persons who stutter: implications for cortico-striato-thalamo-cortical dysfunction

The basal ganglia and cortico-striato-thalamo-cortical connections are known to play a critical role in sequence skill learning and increasing automaticity over practice. The current paper reviews four studies comparing the sequence skill learning and the transition to automaticity of persons who stutter (PWS) and fluent speakers (PNS) over practice. Studies One and Two found PWS to have poor finger tap sequencing skill and nonsense syllable sequencing skill after practice, and on retention and transfer tests relative to PNS. Studies Three and Four found PWS to be significantly less accurate and/or significantly slower after practice on dual tasks requiring concurrent sequencing and colour recognition over practice relative to PNS. Evidence of PWS' deficits in sequence skill learning and automaticity development support the hypothesis that dysfunction in cortico-striato-thalamo-cortical connections may be one etiological component in the development and maintenance of stuttering.

EDUCATIONAL OBJECTIVES

As a result of this activity, the reader will: (1) be able to articulate the research regarding the basal ganglia system relating to sequence skill learning; (2) be able to summarize the research on stuttering with indications of sequence skill learning deficits; and (3) be able to discuss basal ganglia mechanisms with relevance for theory of stuttering.

Identification of traits associated with stuttering

Stuttering has been considered a heritable disorder since the 1930s. There have been different models of transmission that have been proposed most involving a polygenic component with or without a major locus. In spite of these models, the characteristics being transmitted are not known. This study used two different tasks-a tapping task that is thought to probe hemispheric differences and a Stroop task, which appears to create interferences in speech motor programming and/or execution. The 48 participants in this study included individuals who stutter, high risk family members and controls for each group. Results indicated that for tapping at a comfortable rate, the experimental groups were significantly different from their control groups and for tapping at a fast rate, the stuttering and high risk groups were different from each other. The results of the Stroop test were not statistically significant.

LEARNING OUTCOMES

Readers will learn about: (1) genetic aspects of stuttering; (2) hemispheric dominance in stuttering and high risk subjects; (3) understanding traits that may be associated with stuttering.

The transition to increased automaticity during finger sequence learning in adult males who stutter

The present study compared the automaticity levels of persons who stutter (PWS) and persons who do not stutter (PNS) on a practiced finger sequencing task under dual task conditions. Automaticity was defined as the amount of attention required for task performance. Twelve PWS and 12 control subjects practiced finger tapping sequences under single and then dual task conditions. Control subjects performed the sequencing task significantly faster and less variably under single versus dual task conditions while PWS' performance was consistently slow and variable (comparable to the dual task performance of control subjects) under both conditions. Control subjects were significantly more accurate on a colour recognition distracter task than PWS under dual task conditions. These results suggested that control subjects transitioned to quick, accurate and increasingly automatic performance on the sequencing task after practice, while PWS did not. Because most stuttering treatment programs for adults include practice and automatization of new motor speech skills, findings of this finger sequencing study and future studies of speech sequence learning may have important implications for how to maximize stuttering treatment effectiveness.

EDUCATIONAL OBJECTIVES

As a result of this activity, the participant will be able to: (1) Define automaticity and explain the importance of dual task paradigms to investigate automaticity; (2) Relate the proposed relationship between motor learning and automaticity as stated by the authors; (3) Summarize the reviewed literature concerning the performance of PWS on dual tasks; and (4) Explain why the ability to transition to automaticity during motor learning may have important clinical implications for stuttering treatment effectiveness.

Gestural overlap in consonant clusters: effects on the fluent speech of stuttering and non-stuttering subjects

This study was designed to investigate if persons who stutter differ from persons who do not stutter in the coproduction of different types of consonant clusters, as measured in the number of dysfluencies and incorrect speech productions, in speech reaction times and in word durations. Based on the Gestural Phonology Model of Browman and Goldstein, two types of consonant clusters were formed: homorganic and heterorganic clusters, both intra-syllabic (CVCC) and inter-syllabic (CVC#CVC). Overall, the results indicated that homorganic clusters elicited more incorrect speech productions and longer reaction times than the heterorganic clusters, but there was no difference between the homorganic and the heterorganic clusters in the word duration data. Persons who stutter showed a higher percentage dysfluencies and a higher percentage incorrect speech productions than PWNS but there were no main group effects in reaction times and word durations. However, there was a significant three-way interaction effect between group, cluster type and cluster place: homorganic clusters elicited longer reaction times than heterorganic clusters, but only in the inter-syllabic condition and only for persons who stutter. These results suggest that the production of two consonants with the same place of articulation across a syllable boundary puts higher demands on motor planning and/or initiation than producing the same cluster at the end of a syllable, in particular for PWS. The findings are discussed in light of current theories on speech motor control in stuttering.

EDUCATIONAL OBJECTIVES

The reader will be able to describe: (1) the effect of gestural overlap between consonant clusters on speech reaction time and word duration of people who do and do not stutter and be able to (2) identify the literature in the field of gestural overlap between consonant clusters.

Evidence for compensation for stuttering by the right frontal operculum

There is recent evidence of focal alteration in fibre tracts underlying the left sensorimotor cortex in persistent developmental stuttering (PDS) [Lancet 360 (2002) 380]. If, as proposed, this anatomical abnormality is the cause of PDS, then overactivation in the right hemisphere seen with functional neuroimaging in stutterers may reflect a compensatory mechanism. To investigate this hypothesis, we performed two functional magnetic resonance imaging (fMRI) experiments. The first showed systematic activation of a single focus in the right frontal operculum (RFO) in PDS subjects during reading, which was not observed in controls. Responses in this region were negatively correlated with the severity of stuttering, suggesting compensation rather than primary dysfunction. Negative correlation was also observed during the baseline task that consisted in passive viewing of meaningless signs, indicating that RFO compensation acts independently of specific demands on motor speech output. The second experiment, that involved a covert semantic decision task, confirmed that RFO activation does not require overt utterances or motor output. In combination these findings suggest that the RFO serves a nonspecific compensatory role rather than one restricted to the final stages of speech production.

Kinematic analyses of speech, orofacial nonspeech, and finger movements in stuttering and nonstuttering adults

This work investigated the hypothesis that neuromotor differences between individuals who stutter and individuals who do not stutter are not limited to the movements involved in speech production. Kinematic data were obtained from gender- and age-matched stuttering (n = 10) and nonstuttering (n = 10) adults during speech movements, orofacial nonspeech movements, and finger movements. All movements were performed in 4 conditions differing in sequence length and location of the target movement within the sequence. Results revealed statistically significant differences between the stuttering and nonstuttering individuals on several measures of lip and jaw closing (but not opening) movements during perceptually fluent speech. The magnitude of these differences varied across different levels of utterance length (larger differences during shorter utterances) and across different locations of the target movement within an utterance (larger differences close to the beginning). Results further revealed statistically significant differences between the stuttering and nonstuttering groups in finger flexion (but not extension) movement duration and peak velocity latency. Overall, findings suggest that differences between stuttering and nonstuttering individuals are not confined to the sensorimotor processes underlying speech production or even movements of the orofacial system in general. Rather, it appears that the groups show generalized differences in the duration of certain goal-directed movements across unrelated motor systems.

The nature and treatment of stuttering as revealed by fMRI A within- and between-group comparison

This article reviews some of our recent functional magnetic resonance imaging (fMRI) studies of stuttering. Using event-related fMRI experiments, we investigated brain activation during speech production. Results of three studies comparing persons who stutter (PWS) and persons who do not stutter (PWNS) are outlined. Their findings point to a region in the right frontal operculum (RFO) that was consistently implicated in stuttering. During overt reading and before fluency shaping therapy, PWS showed higher and more distributed neuronal activation than PWNS. Immediately after therapy differential activations were even more distributed and left sided. They extended to frontal, temporal, and parietal regions, anterior cingulate, insula, and putamen. These over-activations were slightly reduced and again more right sided two years after therapy. Left frontal deactivations remained stable over two years of observation, and therefore possibly indicate a dysfunction. After therapy, we noted higher activations in persons who stutter moderately than in those who stutter severely. These activations might reflect patterns of compensation. We discuss why these findings suggest that fluency-inducing techniques might synchronize a disturbed signal transmission between auditory, speech motor planning, and motor areas.

EDUCATIONAL OBJECTIVES

The reader will learn about and be able to: (1) identify regions of brain activations and deactivations specific for PWS; (2) describe brain activation changes induced by fluency shaping therapy; and (3) discuss the correlation between stuttering severity and brain activation.

Intentional and attentional dynamics of speech-hand coordination

Interest is rapidly growing in the hypothesis that natural language emerged from a more primitive set of linguistic acts based primarily on manual activity and hand gestures. Increasingly, researchers are investigating how hemispheric asymmetries are related to attentional and manual asymmetries (i.e., handedness). Both speech perception and production have origins in the dynamical generative movements of the vocal tract known as articulatory gestures. Thus, the notion of a "gesture" can be extended to both hand movements and speech articulation. The generative actions of the hands and vocal tract can therefore provide a basis for the (direct) perception of linguistic acts. Such gestures are best described using the methods of dynamical systems analysis since both perception and production can be described using the same commensurate language. Experiments were conducted using a phase transition paradigm to examine the coordination of speech-hand gestures in both left- and right-handed individuals. Results address coordination (in-phase vs. anti-phase), hand (left vs. right), lateralization (left vs. right hemisphere), focus of attention (speech vs. tapping), and how dynamical constraints provide a foundation for human communicative acts. Predictions from the asymmetric HKB equation confirm the attentional basis of functional asymmetry. Of significance is a new understanding of the role of perceived synchrony (p-centres) during intentional cases of gestural coordination.

Statistical power in stuttering research: a tutorial

The capacity to make reliable inductive statements about populations is critical for the advancement of scientific knowledge. An important contribution to that advancement of knowledge is determining that effects are either present or not present in populations. Statistical power is an important methodological qualification for any research that presents statistical results, and particularly so for research that presents null results. In this paper we describe the statistical concept of power, outline parameters of research that influence it, and demonstrate how it is calculated. With reference to selected published research, attention is drawn to the problems associated with a body of underpowered research, one being that population effects may go undetected. One way to prevent this problem is to calculate power a priori in planning research and include confidence intervals when presenting the results of research. However, it is difficult, if not impossible in many cases, to obtain high participant numbers for communication disorders of low prevalence such as stuttering. With this in mind, the paper concludes with an attempt to open discussion about ways to redress the problems associated with statistical power.

Speech-motor control and interhemispheric relations in recovered and persistent stuttering

The neurological basis of stuttering is associated with anomalies of interhemispheric relations and of the neural mechanisms of speech-motor control, specifically those involving the supplementary motor area (SMA). Stuttering typically develops through childhood and adolescence but many children will recover without formal treatment or intervention. The hypothesis that such spontaneous recovery is related to a maturation of the SMA is explored. Four experimental tasks were performed by adults whose stuttering has persisted, adults who reported having stuttered as children, and a control group of adults who reported never having stuttered. A Sequence Reproduction Finger Tapping task (Webster, 1986) and a Bimanual Crank Turning task (Preilowski, 1972) examined the functioning of the SMA, and 2 Divided Visual Field tasks examined asymmetries of hemispheric activation. The overall pattern of results for persistent stutterers compared to nonstutterers was consistent with motor-perceptual anomalies previously reported in the literature. The Bimanual Crank Turning task revealed additionally that the bimanual coordination deficits reported in adults who stutter are kinesthetically based and mediated through anterior callosal systems, including the SMA. Ex-stutterers were similar to nonstutterers in their performance of the motor control tasks, but similar to persistent stutterers in perceptual asymmetries associated with Divided Visual Field tasks. Taken together, the results from the four experimental tasks support the general hypothesis that an anomaly in interhemispheric relations and a deficit in the mechanisms of speech-motor control are each a necessary but not sufficient condition for stuttering and that recovery from childhood stuttering reflects a maturation of the mechanisms of speech-motor control.

Lip movement in patients with a history of unilateral cleft lip

OBJECTIVE

The influence of a repaired cleft lip on the stability of coordination between upper and lower lip in nonspeech and speech tasks was investigated.

DESIGN

First, we looked at the effects of a secondary cleft lip repair in three individuals. Second, we compared subjects with a history of repaired unilateral cleft lip and subjects with no history of cleft lip (controls). Lip coordination was measured using continuous estimates of relative phase.

PARTICIPANTS

Subjects were nine children and adolescents with a primary unilateral cleft lip and palate repair and 4 participants without cleft matched for age across different age categories.

RESULTS

In general, the averaged relative phase angle (RPA) angle values were smaller than 180 degrees, indicating an upper lip lead for lip closure. Controls showed a tendency toward a more symmetric type of coordination (close to 180 degrees), compared with subjects with a repaired unilateral cleft lip. The controls also showed less variation in coordination between the lips. For the more complex speech tasks, a general increase in variability of the RPA values for all subjects was observed, most likely suggesting a more flexible type of coordination. Regarding the effect of a secondary cleft lip repair, only one of the three patients showed a clearly less symmetric and less stable type of coordination, compared with preoperation results.

CONCLUSIONS

There appear to be differences in lip coordination between speakers without and speakers with a repaired unilateral cleft lip. Furthermore, it seems that the stability of lip coordination tends to increase with age.

Research on speech motor control and its disorders: a review and prospective

This paper reviews issues in speech motor control and a class of communication disorders known as motor speech disorders. Speech motor control refers to the systems and strategies that regulate the production of speech, including the planning and preparation of movements (sometimes called motor programming) and the execution of movement plans to result in muscle contractions and structural displacements. Traditionally, speech motor control is distinguished from phonologic operations, but in some recent phonologic theories, there is a deliberate blurring of the boundaries between phonologic representation and motor functions. Moreover, there is continuing discussion in the literature as to whether a given motor speech disorder (especially apraxia of speech and stuttering) should be understood at the phonologic level, the motoric level, or both of these. The motor speech disorders considered here include: the dysarthrias, apraxia of speech, developmental apraxia of speech, developmental stuttering, acquired (neurogenic and psychogenic) stuttering, and cluttering.

Acoustic duration changes associated with two types of treatment for children who stutter

The purpose of this study was (a) to examine in young children the effects of Speech Motor Training (SMT) on selected temporal acoustic durations considered to be related to speech motor programming, (b) to compare the speech motor effects of that treatment with those of a treatment of childhood stuttering that did not directly incorporate speech motor control training (Extended Length of Utterance [ELU]), and (c) to examine the relation of acoustic duration changes to reduction of stuttering. Twelve children who stutter were recorded while repeating syllable sets /see text/ and /see text/ before and after SMT (n = 6) or ELU treatment (n = 6). Children who did not stutter served as matched reference groups. The syllables beginning with /p/ and /t/ were used as tokens for the acoustic measurement. Five measures served as indicators of temporal aspects of speech motor performance: vowel duration, stop gap duration, voice onset time, stop gap/vowel duration ratio, and total token duration. Results indicated that following SMT there was a significant increase in vowel duration and some reduction in stop gap duration that resulted in significantly reduced stop gap/vowel duration ratios. These acoustic effects were consistent across most participants. The ELU treatment reduced stuttering more than the SMT, but was not accompanied by significant effects on the selected temporal acoustic measures. These findings are compared with previous findings of increased vowel durations associated with fluency enhancement and stuttering treatment. We speculate that the increased vowel durations allow more time for speech motor planning and that stuttering is reduced moderately as a by-product of longer vowel durations. The mechanism(s) by which ELU treatment reduces stuttering did not appear to be captured by the dependent variables measured in this study.

Utterance rate and linguistic properties as determinants of lexical dysfluencies in children who stutter

Two important determinants of variation in stuttering frequency are utterance rate and the linguistic properties of the words being spoken. Little is known how these determinants interrelate. It is hypothesized that those linguistic factors that lead to change in word duration, alter utterance rate locally within an utterance that then gives rise to an increase in stuttering frequency. According to the hypothesis, utterance rate variation should occur locally within the linguistic segments in an utterance that is known to increase the likelihood of stuttering. The hypothesis is tested using length of tone unit as the linguistic factor. Three predictions are confirmed: Utterance rate varies locally within the tone units and this local variation affects stuttering frequency; stuttering frequency is positively related to the length of tone units; variations in utterance rate are correlated with tone unit length. Alternative theoretical formulations of these findings are considered.

Adaptation of stuttering frequency during repeated readings: associated changes in acoustic parameters of perceptually fluent speech

This study is part of a series investigating the hypothesis that stuttering adaptation is a result of motor learning. Previous investigations indicate that nonspeech motor learning typically is associated with an increase in speed of performance. Previous investigations of stuttering, on the other hand, indicate that improvements in fluency during most fluency-enhancing conditions or after stuttering treatment tend to be associated with decreased speech rate, increased duration of specific acoustic segments, and decreased vowel duration variability. The present acoustic findings, obtained from 8 individuals who stutter, reveal that speech adjustments occurring during adaptation differ from those reported for other fluency-enhancing conditions or stuttering treatment. Instead, the observed changes are consistent with those occurring during skill improvements for nonspeech motor tasks and, thus, with a motor learning hypothesis of stuttering adaptation. During the last of 6 repeated readings, a statistically significant increase in articulation rate was observed, together with a decrease in word duration, vowel duration, and consonant-vowel (CV) transition extent. Other adjustments showing relatively consistent trends across individual subjects included decreased CV transition rate and duration, and increased variability of both CV transition extent and vowel duration.

Differences in bimanual coordination associated with stuttering

The motor coordination of adults who stutter was examined in the performance of a bimanual movement task. Fifteen subjects who stutter and 15 matched subjects who do not stutter performed three trials of a bimanual finger movement task. Subjects were required to produce a flexion and extension movement of the metacarpophalangeal joint of each index finger in rhythm to a metronome. The rate of movement increased during the 70 s trial. Stutterers could maintain movements at the prescribed rate as well as nonstutterers; however, stutterers moved with less amplitude and peak velocity. In addition, dynamical analysis revealed that subjects who stutter exhibited greater relative phase variability than subjects who do not stutter. These results shed new light on the mixed results of earlier studies on nonspeech motor performance of individuals who stutter and suggest that there are strategic differences as well as coordination differences that should be observable across a variety on motor tasks requiring coordination of multiple effectors.

Lexicalization in adults who stutter

Three recent theories have implicated lexical processing failures as a possible source of fluency disruption in persons who stutter. Two experiments that bear upon these theories are reported. Both evaluate the effects on speech response latency of picture naming tasks designed to place selective demands on lexicalization: Experiment I, effects of one-word versus two-word responses; Experiment II, effects of a word's frequency of occurrence versus its number of syllables. Twelve adults who stutter and 12 with normally fluent speech participated in each experiment. In Experiment I, increases in naming latency for two-word (noun + verb) versus one-word (noun or verb) responses showed that demands for parallel processing did not differentiate the experimental groups. However, the between-group difference, showing longer latencies among those who stutter, was six times greater for the verb, than for the noun, task. Moreover, the group difference for verbs fully accounted for the size of the difference in the two-word task. Experiment II showed that the relative increase in naming latency associated with the word frequency effect versus the syllable latency effect was significantly greater in the stuttering than the nonstuttering group. Outcomes of the two experiments suggest that during lexicalization, as early as the L1 stage and first phase of L2, slow processing could serve to disrupt fluency in some persons who stutter. Under certain conditions, as specified in the three theories cited, such disruptions could set the occasion for stutter events.