Dual tasking and stuttering: from the laboratory to the clinic

Adults Who Stutter Show Diminished Word Fluency, Regardless of Mode

PURPOSE

Language abilities have long been thought to be weaker in adults who stutter (AWS) compared to adults who do not stutter (AWNS). However, it is unknown whether modality affects language performance by AWS in time pressure situations. This study aimed to examine lexical access and retrieval abilities of AWS in oral and typed modes.

METHOD

Fifteen AWS and 15 well-matched AWNS completed computer-administered letter fluency tasks. Adults were asked to orally produce words that began with one of two letter targets and type words that began with one of two alternate letters. Conditions were counterbalanced across participants.

RESULTS

Generalized linear mixed-effects models were evaluated to determine the effects of group (AWS/AWNS), mode (oral/typed), and expressive vocabulary on letter fluency performance. Group predicted letter fluency such that AWS generated fewer items on both the oral and typed letter fluency tasks. Mode did not impact letter fluency results. Expressive Vocabulary Test scores predicted letter fluency similarly in both AWS and AWNS.

CONCLUSIONS

AWS were not penalized by oral task demands. AWS generated fewer items on the letter fluency tasks regardless of response mode, suggesting that they have weaker lexical access abilities. Furthermore, better expressive vocabulary skills were associated with better letter fluency performance in both groups.

Comparison of Stuttering Severity and Anxiety During Standard and Challenge Phone Calls

PURPOSE

This study was designed to answer three questions. (a) Does percentage of syllables stuttered (%SS) differ between standard and challenge phone calls. (b) Does anxiety differ between standard and challenge phone calls. (c) Is there a relationship between %SS and anxiety during standard and challenge phone calls?

METHOD

Participants were 230 adults diagnosed with stuttering, who were participants from five clinical trials. Each participant received two 10-min phone calls at pretreatment and a further two phone calls 6 months or 20 weeks postrandomization. One phone call was standard, and the other presented challenge: occasionally disagreeing with, interrupting, and talking over participants, or asking for clarification of their views.

RESULTS

Statistically significant, but clinically minor, increases of %SS and anxiety occurred during the challenge phone calls. There was a statistically significant association between %SS and anxiety.

CONCLUSIONS

Variable phone call procedures to assess stuttering severity in clinical trials are not likely to spuriously inflate or deflate treatment outcomes to a clinically important extent. Regardless, the present results suggest that there is statistical merit in controlling the nature of phone calls during clinical trials with the simple and replicable method developed in this report. Additionally, there is procedural merit in the challenge phone call procedure; it is a more valid representation of the challenges of everyday speech than the standard procedure. However, a disadvantage of the challenge phone call procedure is the practical issues associated with its use. The clinical and theoretical applications of the results are discussed.

Contemporary Theories of Stuttering Development

The article presents a theoretical analysis of contemporary models of persistent stuttering development in children and adults at the current period of development of science. The accumulated amount of scientific knowledge suggests that stuttering has a neurological basis: it is associated with disorders in the structure and function of the brain. On this basis, there have been emerged models of stuttering that link the cause of a speech disorder with an unstable speech motor system. Theories and models of stuttering based on cognitive and language processing are likely to be useful in that they have explanatory power in relation to the mechanisms that play an important role in the production of key symptoms of stuttering. Considering that stuttering is a complex disorder, the logical result of this was the proposal of multifactorial models of impaired speech fluency. The presented overview may be useful to psychiatrists, clinical psychologists, speech therapists, teachers, and practitioners interacting with children and adults with stuttering and other speech fluency disorders.

Speech fluency in bilinguals who stutter: Language proficiency and attentional demands as mediating factors

PURPOSE

The current study examines how speech disfluencies manifest themselves in the two languages of bilingual persons who stutter, starting from the hypothesis that stuttering is associated with an attentional deficit at the level of speech production.

METHODS

Twenty-eight bilingual people who stutter performed a spontaneous and a controlled speech production task, once in their dominant and once in their non-dominant language. The controlled production task (i.e. a network description task) was carried out once under a full-attention condition and once under a divided-attention condition where a non-linguistic, pitch discrimination task was performed simultaneously.

RESULTS

In both the spontaneous and the controlled speech task, bilingual persons who stutter produced more (typical and stuttering-like) disfluencies in their L2 than in their L1. Furthermore, whereas the typical disfluencies increased when attention was directed away from speech production, stuttering-like disfluencies decreased. This effect was however restricted to L2. In addition, L2 proficiency was generally found to be a predicting factor, with higher proficiency leading to fewer disfluencies.

CONCLUSIONS

These results suggest that speaking in a non-dominant language increases both typical and stuttering-like disfluencies in bilingual persons who stutter, but also that these two types of dysfluencies differ regarding their attentional origins. Our findings offer further support for attentional accounts of stuttering and have both theoretical and clinical implications.

Bilinguals who stutter: A cognitive perspective

PURPOSE

Brain differences, both in structure and executive functioning, have been found in both developmental stuttering and bilingualism. However, the etiology of stuttering remains unknown. The early suggestion that stuttering is a result of brain dysfunction has since received support from various behavioral and neuroimaging studies that have revealed functional and structural brain changes in monolinguals who stutter (MWS). In addition, MWS appear to show deficits in executive control. However, there is a lack of data on bilinguals who stutter (BWS). This literature review is intended to provide an overview of both stuttering and bilingualism as well as synthesize areas of overlap among both lines of research and highlight knowledge gaps in the current literature.

METHODS

A systematic literature review on both stuttering and bilingualism studies was conducted, searching for articles containing "stuttering" and/or "bilingualism" and either "brain", "executive functions", "executive control", "motor control", "cognitive reserve", or "brain reserve" in the PubMed database. Additional studies were found by examining the reference list of studies that met the inclusion criteria.

RESULTS

A total of 148 references that met the criteria for inclusion in this paper were used in the review. A comparison of the impact of stuttering or bilingualism on the brain are discussed.

CONCLUSION

Previous research examining a potential bilingual advantage for BWS is mixed. However, if such an advantage does exist, it appears to offset potential deficits in executive functioning that may be associated with stuttering.

The Speaker's Experience of Stuttering: Measuring Spontaneity

Purpose This study measures the experience of spontaneous speech in everyday speaking situations. Spontaneity of speech is a novel concept developed to account for the subjective experience of speaking. Spontaneous speech is characterized by little premeditation and effortless production, and it is enjoyable and meaningful. Attention is not directed on the physical production of speech. Spontaneity is intended to be distinct from fluency so that it can be used to describe both stuttered and fluent speech. This is the first study to attempt to measure the concept of spontaneity of speech. Method The experience sampling method was used with 44 people who stutter. They were surveyed five times a day for 1 week through their cell phones. They reported on their perceived spontaneity, fluency, and speaking context. Results Results indicate that spontaneity and fluency are independent, though correlated, constructs that vary with context. Importantly, an increase in spontaneity significantly decreases the adverse impact of stuttering on people's lives. Fluency did not significantly affect adverse life impact of stuttering. Conclusion Findings support a theoretical construct of spontaneity that is distinct from speech fluency and that can inform our views of stuttering and approaches to stuttering treatment.

Disfluencies and Strategies Used by People Who Stutter During a Working Memory Task

Purpose Working memory (WM) deficits are implicated in various communication disorders, including stuttering. The reading span test (RST) measures WM capacity with the dual task of reading sentences aloud and remembering target words. This study demonstrates a difference in strategy between people who stutter (PWS) and people who do not stutter (PWNS) in performing the RST. The impact of the effective strategy and the stuttering-like disfluencies during the RST were investigated. Method Twenty-six PWS and 24 people who do not stutter performed the RST and a simple reading aloud task. After the RST, they were asked which strategy ("imagery" or "rehearsal") they had used in order to remember the target words during the task. Results The proportion of those who used an "imagery" strategy during the RST was significantly smaller in the PWS group. However, the RST scores of those who used an "imagery" strategy were significantly higher than the RST scores of those who used a "rehearsal" strategy in both groups. The "rehearsal" users were asked to undertake one more RST with an "imagery" strategy, which resulted in an increased score for both groups. The disfluency frequency of the PWS group was significantly reduced during the RST than during the oral reading task, irrespective of the employed strategy. Conclusions PWS tended to use the less effective verbal "rehearsal" strategy during the RST. The differential effects of switching strategies on the measured WM capacity and on the disfluency rate suggest that the enhanced fluency during the RST would be mostly attributable to the reduced attention to speech motor control. Therefore, the use of the "imagery" strategy and focusing on the contents of communication, away from speech motor control, should help PWS communicate better in daily conversation.

Effects of different attention tasks on concurrent speech in adults who stutter and fluent controls

PURPOSE

Motor theories indicate that focusing attention on well-practiced movements interferes with skilled performance; however, specific forms of attention (alerting vs. orienting vs. executive control) associated with this effect are not well understood. The present study explored this question in relation to stuttering, and examined whether dual task conditions that engaged sustained attention or working memory (WM) affected speech fluency in different ways. We also considered whether fluency changes were associated with changes in speech rate and language.

METHODS

Nineteen adults who stutter (AWS) and 20 controls produced spontaneous speech under a baseline condition and two dual task conditions: one involving a sustained attention task, the other involving WM demands.

RESULTS

Both groups produced fewer stutter-like disfluencies under dual task relative to baseline conditions and this reduction did not differ between the two dual tasks (attention vs. WM). Speech rate and language variables, which were potentially influenced by attention conditions, were not affected by dual tasks in the same way as disfluencies, and appeared to be unassociated with fluency results.

CONCLUSIONS

Findings indicate that atypical disfluencies decrease when attention is divided, even when secondary task demands are minimal, as they were in the sustained attention task. For simple secondary tasks, fluency changes do not appear to be a byproduct of slowed rate and are not accompanied by observable changes in language. These results demonstrate that simple manipulations of attention can induce measurable effects on aspects of speech production, and may be a useful tool for facilitating fluency in clinical intervention.

Phonological working memory in developmental stuttering: Potential insights from the neurobiology of language and cognition

The current review examines how neurobiological models of language and cognition could shed light on the role of phonological working memory (PWM) in developmental stuttering (DS). Toward that aim, we review Baddeley's influential multicomponent model of PWM and evidence for load-dependent differences between children and adults who stutter and typically fluent speakers in nonword repetition and dual-task paradigms. We suggest that, while nonword repetition and dual-task findings implicate processes related to PWM, it is unclear from behavioral studies alone what mechanisms are involved. To address how PWM could be related to speech output in DS, a third section reviews neurobiological models of language proposing that PWM is an emergent property of cyclic sensory and motor buffers in the dorsal stream critical for speech production. We propose that anomalous sensorimotor timing could potentially interrupt both fluent speech in DS and the emergent properties of PWM. To further address the role of attention and executive function in PWM and DS, we also review neurobiological models proposing that prefrontal cortex (PFC) and basal ganglia (BG) function to facilitate working memory under distracting conditions and neuroimaging evidence implicating the PFC and BG in stuttering. Finally, we argue that cognitive-behavioral differences in nonword repetition and dual-tasks are consistent with the involvement of neurocognitive networks related to executive function and sensorimotor integration in PWM. We suggest progress in understanding the relationship between stuttering and PWM may be accomplished using high-temporal resolution electromagnetic experimental approaches.

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.

Estimates of functional cerebral hemispheric differences in monolingual and bilingual people who stutter: Dual-task paradigm

The inter-relationship of stuttering and bilingualism to functional cerebral hemispheric processing was examined on a dual-task paradigm. Eighty native German (L1) speakers, half of whom were sequential bilinguals (L2 = English), were recruited. The participants (mean age = 38.9 years) were organised into four different groups according to speech status and language ability: 20 bilinguals who stutter (BWS), 20 monolinguals who stutter (MWS), 20 bilinguals who do not stutter (BWNS), and 20 monolinguals who do not stutter (MWNS). All participants completed a dual-task paradigm involving simultaneous speaking and finger tapping. No performance differences between BWS and BWNS were found. In contrast, MWS showed greater dual-task interference compared to BWS and MWNS, as well as greater right- than left-hand disruption. A prevailing finding was that bilingualism seems to offset deficits in executive functioning associated with stuttering. Cognitive reserve may have been reflected in the present study, resulting in a bilingual advantage.

Involvement of the Central Cognitive Mechanism in Word Production in Adults Who Stutter

PURPOSE

The study examined whether semantic and phonological encoding processes were capacity demanding, involving the central cognitive mechanism, in adults who do and do not stutter (AWS and NS) to better understand the role of cognitive demand in linguistic processing and stuttering. We asked (a) whether the two linguistic processes in AWS are capacity demanding, which can temporally disrupt the processing of a concurrent nonlinguistic task, and (b) whether AWS and NS show similar patterns of temporal disruption in the two processes.

METHOD

Twenty AWS and 20 matched NS participated in the study. We examined semantic interference and phonological facilitation effects, using the picture-word interference paradigm, under concurrent and sequential processing of a secondary, nonlinguistic task.

RESULTS

Both AWS and NS showed statistically significant semantic interference and phonological facilitation effects, and both effects caused temporal disruption to the processing of a secondary task to the predicted extent.

CONCLUSIONS

The observed result patterns in both AWS and NS suggest that both semantic and phonological encoding processes are capacity demanding and can be vulnerable to concurrent processing demands. This finding on NS is inconsistent with the current literature on young, fluent adults and warrants further investigation.

Estimates of functional cerebral hemispheric differences in monolingual and bilingual people who stutter: Visual hemifield paradigm

The relationship between stuttering and bilingualism to functional cerebral hemispheric processing was examined using a visual hemifield paradigm. Eighty native German speakers, half of whom were also proficient speakers of English as a second language (L2), were recruited. The participants were organised into four different groups according to speech status and language ability: 20 monolinguals who stutter, 20 bilinguals who stutter, 20 monolinguals who do not stutter, and 20 bilinguals who do not stutter. All participants completed a task involving selective identification of common objects simultaneously presented to both visual fields. Overall, an LVF advantage was observed across all groups with no significant group differences in regard to hemispheric asymmetry. However, both bilingual groups showed faster reaction times and fewer identification errors than the two monolingual groups. A prevailing finding was that bilingualism seems to offset deficits in executive functioning associated with stuttering. Hence, the results lend support to previous findings implicating the benefits of bilingualism.

Does Working Memory Enhance or Interfere With Speech Fluency in Adults Who Do and Do Not Stutter? Evidence From a Dual-Task Paradigm

PURPOSE

The present study examined whether engaging working memory in a secondary task benefits speech fluency. Effects of dual-task conditions on speech fluency, rate, and errors were examined with respect to predictions derived from three related theoretical accounts of disfluencies.

METHOD

Nineteen adults who stutter and twenty adults who do not stutter participated in the study. All participants completed 2 baseline tasks: a continuous-speaking task and a working-memory (WM) task involving manipulations of domain, load, and interstimulus interval. In the dual-task portion of the experiment, participants simultaneously performed the speaking task with each unique combination of WM conditions.

RESULTS

All speakers showed similar fluency benefits and decrements in WM accuracy as a result of dual-task conditions. Fluency effects were specific to atypical forms of disfluency and were comparable across WM-task manipulations. Changes in fluency were accompanied by reductions in speaking rate but not by corresponding changes in overt errors.

CONCLUSIONS

Findings suggest that WM contributes to disfluencies regardless of stuttering status and that engaging WM resources while speaking enhances fluency. Further research is needed to verify the cognitive mechanism involved in this effect and to determine how these findings can best inform clinical intervention.

Theory and therapy in stuttering: a complex relationship

There are many treatments currently available for stuttering, for both children and adults. These range from direct interventions intended to reduce the severity and/or frequency of the speech behaviors of stuttering, to those intended to alleviate the anxiety and other mental health issues that can accompany the disorder. However, as there are little supporting data for many of these treatments, there is little consensus about which to use. Another way to evaluate stuttering treatments is to explore the extent to which they address the cause of the disorder. However, the cause of stuttering is not yet known. In this theoretical paper, a 3-factor causal model is presented, to which the mechanisms thought to be driving different treatments are then aligned. The model is innovative, in that it attempts to explain moments of stuttering. It is argued that all causal factors must be operating at each moment of stuttering. The model is intended as a new way of looking at cause, and how treatments may address cause. It is hoped this will stimulate discussion and lead to further lines of inquiry.

EDUCATIONAL OBJECTIVES

The reader will be able to: (a) describe the P&A 3-factor causal model of moments of stuttering; (b) state how indirect direct stuttering treatments relate to cause, according to the P&A model; (c) describe how direct stuttering treatments relate to cause, according to the P&A model; (d) state the purpose of cognitive behavior therapy; and (e) describe at least one suggestion for further research arising from the P&A model.