Inducement of fluent speech in persons who stutter via visual choral speech

The effect of manual movements on stuttering in individuals with down syndrome

PURPOSE

Stuttering may disrupt the speech of individuals with Down syndrome (DS), but standard stuttering therapies may be less adapted to these clients' needs. This study examined if their strength in gesture use can lead to the development of a new stuttering therapy.

METHOD

Eighteen individuals with DS who stutter participated in an experimental task. During this task, they produced sentences in three different conditions: once without the ability to use gestures, once while moving the mouth of a hand puppet synchronous with their speech, and once while making beat gestures along their speech. Stuttering frequency was measured and compared between conditions while controlling for the effect of articulation rate.

RESULTS

The experimental hand puppet and beat condition did not affect the stuttering frequency, but the covariate articulation rate did. An exploratory posthoc analysis showed that the articulation rate decreased during the experimental hand puppet and beat condition. Manual movements in the present task might only induce fluency through articulation rate reduction. However, analyses at individual level show significant interindividual variability.

CONCLUSION

Individual analyses show that effect on stuttering frequency cannot be attributed entirely to articulation rate reduction and that beat gestures might still play a role. However, at this point, there is not enough direct evidence to implement beat gestures in current stuttering therapy.

Phonetic versus spatial processes during motor-oriented imitations of visuo-labial and visuo-lingual speech: A functional near-infrared spectroscopy study

While a large amount of research has studied the facilitation of visual speech on auditory speech recognition, few have investigated the processing of visual speech gestures in motor-oriented tasks that focus on the spatial and motor features of the articulator actions instead of the phonetic features of auditory and visual speech. The current study examined the engagement of spatial and phonetic processing of visual speech in a motor-oriented speech imitation task. Functional near-infrared spectroscopy (fNIRS) was used to measure the haemodynamic activities related to spatial processing and audiovisual integration in the superior parietal lobe (SPL) and the posterior superior/middle temporal gyrus (pSTG/pMTG) respectively. In addition, visuo-labial and visuo-lingual speech were compared with examine the influence of visual familiarity and audiovisual association on the processes in question. fNIRS revealed significant activations in the SPL but found no supra-additive audiovisual activations in the pSTG/pMTG, suggesting that the processing of audiovisual speech stimuli was primarily focused on spatial processes related to action comprehension and preparation, whereas phonetic processes related to audiovisual integration was minimal. Comparisons between visuo-labial and visuo-lingual speech imitations revealed no significant difference in the activation of the SPL or the pSTG/pMTG, suggesting that a higher degree of visual familiarity and audiovisual association did not significantly influence how visuo-labial speech was processed compared with visuo-lingual speech. The current study offered insights on the pattern of visual-speech processing under a motor-oriented task objective and provided further evidence for the modulation of multimodal speech integration by voluntary selective attention and task objective.

Coarticulatory Aspects of the Fluent Speech of French and Italian People Who Stutter Under Altered Auditory Feedback

A number of studies have shown that phonetic peculiarities, especially at the coarticulation level, exist in the disfluent as well as in the perceptively fluent speech of people who stutter (PWS). However, results from fluent speech are very disparate and not easily interpretable. Are the coarticulatory features observed in fluent speech of PWS a manifestation of the disorder, or rather a compensation for the disorder itself? The purpose of the present study is to investigate the coarticulatory behavior in the fluent speech of PWS in the attempt to answer the question on its symptomatic or adaptive nature. In order to achieve this, we have studied the speech of 21 adult PWS (10 French and 11 Italian) compared to that of 20 fluent adults (10 French and 10 Italian). The participants had to repeat simple CV syllables in short carrier sentences, where C = /b, d, g/ and V = /a, i, u/. Crucially, this repetition task was performed in order to compare fluent speech coarticulation of PWS to that of PWNS, and to compare the coarticulation of PWS under a condition with normal auditory feedback (NAF) and under a fluency-enhancing condition due to an altered auditory feedback (AAF). This is the first study, to our knowledge, to investigate the coarticulation behavior under AAF. The degree of coarticulation was measured by means of the Locus Equations (LE). The coarticulation degree observed in fluent PWS speech is lower than that of the PWNS, and, more importantly, in AAF condition, PWS coarticulation appears even weaker than in the NAF condition. The results allow to interpret the lower degree of coarticulation found in fluent speech of PWS under NAF condition as a compensation for the disorder, based on the fact that PWS’s coarticulation is weakening in fluency-enhancing conditions, further away from the degree of coarticulation observed in PWNS. Since a lower degree of coarticulation is associated to a greater separation between the places of articulation of the consonant and the vowel, these results are compatible with the hypothesis that larger articulatory movements could be responsible for the stabilization of the PWS speech motor system, increasing the kinesthetic feedback from the effector system. This interpretation shares with a number of relatively recent proposal the idea that stuttering derives from an impaired feedforward (open-loop) control system, which makes PWS rely more heavily on a feedback-based (closed loop) motor control strategy.

Retraining speech production and fluency in non-fluent/agrammatic primary progressive aphasia

The non-fluent/agrammatic variant of primary progressive aphasia (nfvPPA) presents with a gradual decline in grammar and motor speech resulting from selective degeneration of speech-language regions in the brain. There has been considerable progress in identifying treatment approaches to remediate language deficits in other primary progressive aphasia variants; however, interventions for the core deficits in nfvPPA have yet to be systematically investigated. Further, the neural mechanisms that support behavioural restitution in the context of neurodegeneration are not well understood. We examined the immediate and long-term benefits of video implemented script training for aphasia (VISTA) in 10 individuals with nfvPPA. The treatment approach involved repeated rehearsal of individualized scripts via structured treatment with a clinician as well as intensive home practice with an audiovisual model using 'speech entrainment'. We evaluated accuracy of script production as well as overall intelligibility and grammaticality for trained and untrained scripts. These measures and standardized test scores were collected at post-treatment and 3-, 6-, and 12-month follow-up visits. Treatment resulted in significant improvement in production of correct, intelligible scripted words for trained topics, a reduction in grammatical errors for trained topics, and an overall increase in intelligibility for trained as well as untrained topics at post-treatment. Follow-up testing revealed maintenance of gains for trained scripts up to 1 year post-treatment on the primary outcome measure. Performance on untrained scripts and standardized tests remained relatively stable during the follow-up period, indicating that treatment helped to stabilize speech and language despite disease progression. To identify neural predictors of responsiveness to intervention, we examined treatment effect sizes relative to grey matter volumes in regions of interest derived from a previously identified speech production network. Regions of significant atrophy within this network included bilateral inferior frontal cortices and supplementary motor area as well as left striatum. Volumes in a left middle/inferior temporal region of interest were significantly correlated with the magnitude of treatment effects. This region, which was relatively spared anatomically in nfvPPA patients, has been implicated in syntactic production as well as visuo-motor facilitation of speech. This is the first group study to document the benefits of behavioural intervention that targets both linguistic and motoric deficits in nfvPPA. Findings indicate that behavioural intervention may result in lasting and generalized improvement of communicative function in individuals with neurodegenerative disease and that the integrity of spared regions within the speech-language network may be an important predictor of treatment response.

Comparison of different speech tasks among adults who stutter and adults who do not stutter

OBJECTIVES

In this study, we compared the performance of both fluent speakers and people who stutter in three different speaking situations: monologue speech, oral reading and choral reading. This study follows the assumption that the neuromotor control of speech can be influenced by external auditory stimuli in both speakers who stutter and speakers who do not stutter.

METHOD

Seventeen adults who stutter and seventeen adults who do not stutter were assessed in three speaking tasks: monologue, oral reading (solo reading aloud) and choral reading (reading in unison with the evaluator). Speech fluency and rate were measured for each task.

RESULTS

The participants who stuttered had a lower frequency of stuttering during choral reading than during monologue and oral reading.

CONCLUSIONS

According to the dual premotor system model, choral speech enhanced fluency by providing external cues for the timing of each syllable compensating for deficient internal cues.

The effects of delayed auditory and visual feedback on speech production

Monitoring the sensory consequences of articulatory movements supports speaking. For example, delaying auditory feedback of a speaker's voice disrupts speech production. Also, there is evidence that this disruption may be decreased by immediate visual feedback, i.e., seeing one's own articulatory movements. It is, however, unknown whether delayed visual feedback affects speech production in fluent speakers. Here, the effects of delayed auditory and visual feedback on speech fluency (i.e., speech rate and errors), vocal control (i.e., intensity and pitch), and speech rhythm were investigated. Participants received delayed (by 200 ms) or immediate auditory feedback, while repeating sentences. Moreover, they received either no visual feedback, immediate visual feedback, or delayed visual feedback (by 200, 400, and 600 ms). Delayed auditory feedback affected fluency, vocal control, and rhythm. Immediate visual feedback had no effect on any of the speech measures when it was combined with delayed auditory feedback. Delayed visual feedback did, however, affect speech fluency when it was combined with delayed auditory feedback. In sum, the findings show that delayed auditory feedback disrupts fluency, vocal control, and rhythm and that delayed visual feedback can strengthen the disruptive effect of delayed auditory feedback on fluency.

Disfluências e velocidade de fala em produção espontânea e em leitura oral em indivíduos gagos e não gagos

OBJETIVO: Investigar e caracterizar a velocidade de fala e as rupturas da fala em situação espontânea e em leitura oral, em indivíduos gagos e não gagos e investigar a relação entre essas variáveis. MÉTODOS: Trinta participantes com idades entre 17 e 59 anos e, no mínimo, oito anos de escolaridade, constituíram o Grupo Estudo, com 15 indivíduos gagos, e o Grupo Controle, com 15 indivíduos não gagos. Os indivíduos do Grupo Controle e do Grupo Estudo foram pareados por idade, gênero e nível de escolaridade. Após anamnese, foram realizadas as seguintes avaliações: neuropsicológica breve, específica da gagueira e específicas da leitura. As disfluências foram analisadas e calculou-se a velocidade da fala espontânea e na leitura oral. RESULTADOS: Ocorreram mais disfluências na fala espontânea que na leitura oral de texto, em ambos os grupos. Em relação à velocidade, no Grupo Controle, a leitura de pseudopalavras e de texto correlacionaram-se positivamente e no Grupo Estudo, todas as variáveis correlacionaram-se positivamente. CONCLUSÃO: A análise da velocidade e das rupturas de fala caracterizou ambos os grupos, tanto em situação de fala espontânea, quanto na leitura que evidencia perfis de desempenho diferenciados pela velocidade de fala, frequência e tipologia das rupturas. A investigação demonstra que indivíduos gagos apresentaram valores mais baixos de velocidade, assim como maior ocorrência de disfluências, tanto na fala espontânea quanto na leitura oral, em comparação com indivíduos não gagos.

The effect of speech rate on stuttering frequency, phonated intervals, speech effort, and speech naturalness during chorus reading

PURPOSE

This study examined the effect of speech rate on phonated intervals (PIs), in order to test whether a reduction in the frequency of short PIs is an important part of the fluency-inducing mechanism of chorus reading. The influence of speech rate on stuttering frequency, speaker-judged speech effort, and listener-judged naturalness was also examined. An added purpose was to determine if chorus reading could be further refined so as to provide a perceptual guide for gauging the level of physical effort exerted during speech production.

METHODS

A repeated-measures design was used to compare data obtained during control reading conditions and during several chorus reading conditions produced at different speech rates. Participants included 8 persons who stutter (PWS) between the ages of 16 and 32 years.

RESULTS

There were significant reductions in the frequency of short PIs from the habitual reading condition during slower chorus conditions, no change when speech rates were matched between habitual reading and chorus conditions, and an increase in the frequency of short PIs during chorus reading produced at a faster rate than the habitual condition. Speech rate did not have an effect on stuttering frequency during chorus reading. In general, speech effort ratings improved and naturalness ratings worsened as speech rate decreased.

CONCLUSION

These results provide evidence that (a) a reduction in the frequency of short PIs is not necessary for fluency improvement during chorus reading, and (b) speech rate may be altered to provide PWS with a more appropriate reference for how physically effortful normally fluent speech production should be. Future investigations should examine the necessity of changes in the activation of neural regions during chorus reading, the possibility of defining individualized units on a 9-point effort scale, and if there are upper and lower speech rate boundaries for receiving ratings of "highly natural sounding" speech during chorus reading.

LEARNING OUTCOMES

The reader will be able to: (1) describe the effect of changes in speech rate on the frequency of short phonated intervals during chorus reading, (2) describe changes to speaker-judged speech effort as speech rate changes during chorus reading, (3) and describe the effect of changes in speech rate on listener-judged naturalness ratings during chorus reading.

Novel tactile feedback to reduce overt stuttering

Stuttering is generally considered to be a speech disorder that affects ∼1% of the global population. Various forms of speech feedback have been shown to reduce overt stuttered speaking, and in particular, second speech signal through speech feedback has drastically reduced utterances of stuttered speech in adults with persistent stuttering. This study reports data for increased overt fluency of speech in an adult stuttering population, whereby the vocalization of the speaker is captured by a microphone or an accelerometer, signal processed, and returned as mechanical tactile speech feedback to the speaker's skin. A repeated measures analysis of variance was used to show that both the microphone and the accelerometer speaking conditions were significantly more fluent than a control (no feedback) condition, with the microphone-driven tactile feedback reducing instances of stuttering by 71% and the accelerometer-driven tactile feedback reducing instances of stuttering by 80%. It is apparent that self-generated tactile feedback can be used to enhance fluency significantly in those who stutter.

Phonation interval modification and speech performance quality during fluency-inducing conditions by adults who stutter

PURPOSE

To relate changes in four variables previously defined as characteristic of normally fluent speech to changes in phonatory behavior during oral reading by persons who stutter (PWS) and normally fluent controls under multiple fluency-inducing (FI) conditions.

METHOD

Twelve PWS and 12 controls each completed 4 ABA experiments. During A phases, participants read normally. B phases were 4 different FI conditions: auditory masking, chorus reading, whispering, and rhythmic stimulation. Dependent variables were the durations of accelerometer-recorded phonated intervals; self-judged speech effort; and observer-judged stuttering frequency, speech rate, and speech naturalness. The method enabled a systematic replication of Ingham et al. (2009).

RESULTS

All FI conditions resulted in decreased stuttering and decreases in the number of short phonated intervals, as compared with baseline conditions, but the only FI condition that satisfied all four characteristics of normally fluent speech was chorus reading. Increases in longer phonated intervals were associated with decreased stuttering but also with poorer naturalness and/or increased speech effort. Previous findings concerning the effects of FI conditions on speech naturalness and effort were replicated.

CONCLUSIONS

Measuring all relevant characteristics of normally fluent speech, in the context of treatments that aim to reduce the occurrence of short-duration PIs, may aid the search for an explanation of the nature of stuttering and may also maximize treatment outcomes for adults who stutter.

LEARNING OUTCOMES

The reader will be able to (1) understand the differential effects of four well established fluency-inducing conditions on the quality of fluency of adult PWS and controls, (2) learn how intervals of phonation are modified during these conditions and (3) how the duration of specific intervals of phonation may be identified for their potential application in stuttering treatment.

Effect of continuous speech and non-speech signals on stuttering frequency in adults who stutter

The inhibitory effects of continuously presented audio signals (/a/, /s/, 1,000 Hz pure-tone) on stuttering were examined. Eleven adults who stutter participated. Participants read four 300-syllable passages (i.e. in the presence and absence of the audio signals). All of the audio signals induced a significant reduction in stuttering frequency relative to the control condition (P = 0.005). A significantly greater reduction in stuttering occurred in the /a/ condition (P < 0.05), while there was no significant difference between the /s/ and 1,000 Hz pure-tone conditions (P > 0.05). These findings are consistent with the notion that the percept of a second signal as speech or non-speech can respectively augment or attenuate the potency for reducing stuttering frequency.

Measurement of speech effort during fluency-inducing conditions in adults who do and do not stutter

PURPOSE

To investigate the effects of 4 fluency-inducing (FI) conditions on self-rated speech effort and other variables in adults who stutter and in normally fluent controls.

METHOD

Twelve adults with persistent stuttering and 12 adults who had never stuttered each completed 4 ABA-format experiments. During A phases, participants read aloud normally. During each B phase, they read aloud in 1 of 4 FI conditions: auditory masking, chorus reading, whispering, and rhythmic speech. Dependent variables included self-judged speech effort and observer-judged stuttering frequency, speech rate, and speech naturalness.

RESULTS

For the persons who stuttered, FI conditions reduced stuttering and speech effort, but only for chorus reading were these improvements obtained without diminishing speech naturalness or speaking rate. By contrast, speech effort increased during all FI conditions for adults who did not stutter.

CONCLUSIONS

Self-rated speech effort differentiated the effects of 4 FI conditions on speech performance for adults who stuttered, with chorus reading best approximating normally fluent speech. More generally, self-ratings of speech effort appeared to constitute an independent, reliable, and validly interpretable dimension of fluency that may be useful in the measurement and treatment of stuttering.

TOWARDS A COMMON NEURAL SUBSTRATE IN THE IMMEDIATE AND EFFECTIVE INHIBITION OF STUTTERING

Stuttering can be effectively inhibited via exogenous sensory signals (e.g., speaking in unison or using altered auditory feedback) or by using endogenous motoric strategies (e.g., singing or therapeutically implementing long vowel prolongations to reduce speech rates). We propose that these channels, which superficially appear to be diametrically opposite, centrally converge in the engagement of mirror neurons for fluent gestural productions. Sensory changes incurred via exogenous speech signals allow for direct engagement of mirror systems, while endogenous motor strategies appear to require significant departures from normal speech production (e.g., highly unnatural or droned speech) to engage mirror systems. Thus, paradoxically, stuttering is prone to resurface during attempts to impose naturalness upon therapeutic speech.

Effects of digital vibrotactile speech feedback on overt stuttering frequency

Fluency-enhancing speech feedback, originating from internally or externally generated sources via auditory or visual sensory modalities is not restricted to a specific sensory modality or signal origination. Research suggests that externally generated digital vibrotactile speech feedback serves as an effective fluency enhancer. The present purpose was to test the fluency-enhancing effects of self-generated digital vibrotactile speech feedback on stuttering frequency. Adults who stutter read passages aloud over the telephone, both with and without digital vibrotactile speech feedback. Digital vibrotactile speech feedback was operationally defined as feeling the vibrations of the thyroid cartilage with the thumb and index finger while speaking. Analysis indicated that self-generated digital vibrotactile speech feedback reduced overt stuttering frequency by an average of 72%. As the specific neural mechanisms associated with stuttering and fluency enhancement from tactile speech feedback remain unknown, theoretical implications and clinical applications were discussed.

The effects of self-generated synchronous and asynchronous visual speech feedback on overt stuttering frequency

PURPOSE

Relatively recent research documents that visual choral speech, which represents an externally generated form of synchronous visual speech feedback, significantly enhanced fluency in those who stutter. As a consequence, it was hypothesized that self-generated synchronous and asynchronous visual speech feedback would likewise enhance fluency. Therefore, the purpose of this study was to investigate the effects of self-generated visual feedback (i.e., synchronous speech feedback with a mirror and asynchronous speech feedback via delayed visual feedback) on overt stuttering frequency in those who stutter.

METHOD

Eight people who stutter (4 males, 4 females), ranging from 18 to 42 years of age participated in this study. Due to the nature of visual speech feedback, the speaking task required that participants recite memorized phrases in control and experimental speaking conditions so that visual attention could be focused on the speech feedback, rather than a written passage. During experimental conditions, participants recited memorized phrases while simultaneously focusing on the movement of their lips, mouth, and jaw within their own synchronous (i.e., mirror) and asynchronous (i.e., delayed video signal) visual speech feedback.

RESULTS

Results indicated that the self-generated visual feedback speaking conditions significantly decreased stuttering frequency (Greenhouse-Geisser p=.000); post hoc orthogonal comparisons revealed no significant differences in stuttering frequency reduction between the synchronous and asynchronous visual feedback speaking conditions (p=.2554).

CONCLUSIONS

These data suggest that synchronous and asynchronous self-generated visual speech feedback is associated with significant reductions in overt stuttering frequency. Study results were discussed relative to existing theoretical models of fluency-enhancement via speech feedback, such as the engagement of mirror neuron networks, the EXPLAN model, and the Dual Premotor System Hypothesis. Further research in the area of self-generated visual speech feedback, as well as theoretical constructs accounting for how exposure to a multi-sensory speech feedback enhances fluency, is warranted.

LEARNING OUTCOMES

: Readers will be able to (1) discuss the multi-sensory nature of fluency-enhancing speech feedback, (2) compare and contrast synchronous and asynchronous self-generated and externally generated visual speech feedback, and (3) compare and contrast self-generated and externally generated visual speech feedback.

Speech disruption during delayed auditory feedback with simultaneous visual feedback

Delayed auditory feedback (DAF) regarding speech can cause dysfluency. The purpose of this study was to explore whether providing visual feedback in addition to DAF would ameliorate speech disruption. Speakers repeated sentences and heard their auditory feedback delayed with and without simultaneous visual feedback. DAF led to increased sentence durations and an increased number of speech disruptions. Although visual feedback did not reduce DAF effects on duration, a promising but nonsignificant trend was observed for fewer speech disruptions when visual feedback was provided. This trend was significant in speakers who were overall less affected by DAF. The results suggest the possibility that speakers strategically use alternative sources of feedback.

The effects of gated speech on the fluency of speakers who stutter

It is known that the speech of people who stutter improves when the speaker's own vocalization is changed while the participant is speaking. One explanation of these effects is the disruptive rhythm hypothesis (DRH). The DRH maintains that the manipulated sound only needs to disturb timing to affect speech control. The experiment investigated whether speech that was gated on and off (interrupted) affected the speech control of speakers who stutter. Eight children who stutter read a passage when they heard their voice normally and when the speech was gated. Fluency was enhanced (fewer errors were made and time to read a set passage was reduced) when speech was interrupted in this way. The results support the DRH.

The inhibition of stuttering via the presentation of natural speech and sinusoidal speech analogs

Sensory signals containing speech or gestural (articulatory) information (e.g., choral speech) have repeatedly been found to be highly effective inhibitors of stuttering. Sine wave analogs of speech consist of a trio of changing pure tones representative of formant frequencies. They are otherwise devoid of traditional speech cues, yet have proven to evoke consistent linguistic percepts in listeners. Thus, we investigated the potency of sinusoidal speech for inhibiting stuttering. Ten adults who stutter read while listening to (a) forward-flowing natural speech; (b) forward-flowing sinusoid analogs of natural speech; (c) reversed natural speech; (d) reversed sinusoid analogs of natural speech; and (e) a continuous 1000 Hz pure tone. The levels of stuttering inhibition achieved using the sinusoidal stimuli were potent and not significantly different from those achieved using natural speech (approximately 50% in forward conditions and approximately 25% in the reversed conditions), suggesting that the patterns of undulating pure tones are sufficient to endow sinusoidal sentences with 'quasi-gestural' qualities. These data highlight the sensitivity of a specialized 'phonetic module' for extracting gestural information from sensory stimuli. Stuttering inhibition is thought to occur when perceived gestural information facilitates fluent productions via the engagement of mirror neurons (e.g., in Broca's area), which appear to play a crucial role in our ability to perceive and produce speech.

Choral reading with filtered speech: effect on stuttering

This study investigated use of choral reading with filtered components of speech and whispered speech on the frequency of stuttering. Three passages read by a normal adult male were lowpass filtered with kneepoint frequencies at 100 Hz (approximate glottal source), 500 Hz (source and first formant), and 1 kHz (source and the first two formants). Along with a whispered passage, a normal passage, and a control condition, these stimuli were used in a repeated-measures design with 12 adult stutterers as they read passages while listening to one of the stimuli. Frequencies of stuttering in each condition were analyzed. The choral speech, the 500-Hz, the 1-kHz, and the whispered speech conditions all decreased the frequency of stuttering while the 100-Hz stimuli did not. It is suggested that articulatory events, chiefly the encoded speech output from the vocal tract, create effective cues and may induce fluent speech in people who stutter.

The effects of temporal modification of second speech signals on stuttering inhibition at two speech rates in adults

The recovery of 'gestural' speech information via the engagement of mirror neurons has been suggested to be the key agent in stuttering inhibition during the presentation of exogenous second speech signals. Based on this hypothesis, we expect the amount of stuttering inhibition to depend on the ease of recovery of exogenous speech gestures. To examine this possibility, linguistically non-congruent second speech signals were temporally compressed and expanded in two experiments. In Experiment 1, 12 participants who stutter read passages aloud at normal and fast speech rates while listening to second speech signals that were 0, 40, 80% compressed, and 40 and 80% expanded. Except for the 80% compressed speech signal, all other stimuli induced significant stuttering inhibition relative to the control condition. The 80% compressed speech signal was the first exogenously presented speech signal that failed to significantly reduce stuttering frequency by 60--70% that has been the case in our research over the years. It was hypothesized that at a compression ratio of 80%, exogenous speech signals generated too many gestures per unit time to allow for adequate gestural recovery via mirror neurons. However, considering that 80% compressed signal was also highly unintelligible, a second experiment was conducted to further examine whether the effects of temporal compression on stuttering inhibition are mediated by speech intelligibility. In Experiment 2, 10 participants who stutter read passages at a normal rate while listening to linguistically non-congruent second speech signals that were compressed by 0, 20, 40, 60, and 80%. Results revealed that 0 and 20% compressed speech signals induced approximately 52% stuttering inhibition. In contrast, compression ratios of 40% and beyond induced only 27% stuttering inhibition although 40 and 60% compressed signals were perceptually intelligible. Our findings suggest that recovery of gestural information is affected by temporal compression before intelligibility starts to decrease.

Gestural recovery and the role of forward and reversed syllabic repetitions as stuttering inhibitors in adults

Instead of being the core stuttering 'problem', syllabic repetitions may be a biological mechanism, or 'solution', to the central involuntary stuttering block. Simply put, stuttering is an endogenous transitory state of 'shadowed speech', a choral speech derivative that allows for a neural release of the central block. To investigate this possibility, 14 adults who stutter read while listening to forward fluent speech, reversed fluent speech, forward stuttered speech, and reversed stuttered speech. All conditions induced significant degrees of stuttering inhibition when compared to a control condition. However, the reversed fluent condition was less powerful than the other three conditions ( approximately 42% vs. approximately 65%) for inhibiting stuttering. Stuttering inhibition appears to proceed by 'gestural recovery', made possible by the presence of an exogenous or 'second' set of speech gestures and engagement of mirror neurons. When reversed fluent speech was used, violations in normal gesture-time relationships (i.e., normal speech entropy) resulted in gestural configurations that apparently were inadequately recovered, and therefore, were not as conducive to high levels of stuttering inhibition. In contrast, high levels of encoding found in the simple syllabic structures of stuttered speech allowed its forward and reversed forms to be equally effective for gestural recovery and stuttering inhibition. The reversal of repeated syllables did not appear to significantly degrade the natural gesture-time relationships (i.e., they were perceptually recognizable). Thus, exogenous speech gestures that displayed near normal gestural relationships allowed for easy recovery and fluent productions via mirror systems, suggesting a more choral-like nature. The importance of syllabic repetitions is highlighted: both their perceived (exogenous) and produced (endogenous) forms appear to be fundamental, surface acoustic manifestations for central stuttering inhibition via the engagement of mirror neurons.

A temporal window for the central inhibition of stuttering via exogenous speech signals in adults

We explored a possible temporal window for central stuttering inhibition via exogenously presented speech signals. Thirteen adults who stutter were asked to read while listening to a continuous vowel /a/, or a repeating 1 s vowel /a/ followed by 1, 3 and 5 s silences. In all conditions, stuttering was significantly reduced. However, the continuous and 1 s repeating conditions showed the greatest reduction in stuttering relative to all other conditions. Furthermore, these conditions did not differ significantly from each other, suggesting a temporal window of at least 1 s for stuttering inhibition induced by a 1 s stimulus. We propose that exogenous speech signals provide an additional speech source that engages mirror neurons for 'on-line' stuttering inhibition during continous speech. Employing dual speech sources results in 'on-line' stuttering inhibition and continuous speech flow. In contrast, endogenous (single source) inhibitory techniques require speech flow to be interrupted and go 'off-line' to derive the mirror neuronal.

Choral speech: the amelioration of stuttering via imitation and the mirror neuronal system

'Choral' speech or speaking in unison is an undeniable phenomenon that immediately induces fluent and natural sounding speech in almost all people who stutter, regardless of linguistic content, situation or audience size. We propose that the choral speech effect is a form direct imitation, a primitive and innate human capacity that is possibly mediated at the neuronal level by 'mirror neurons'. Mirror systems link observations and actions are considered by many to be a neuronal substrate for gestural language acquisition, as well as forming the basis for many learned behaviors, thus possibly playing a vital role in ensuring survival during infancy. The engagement of these systems allows gestural sequences, including speech, to be fluently replicated. Choral speech and its permutations use the capacity for fluent imitation in people who stutter via a 'loose' gestural matching system in which gestures in the external signal possessing cues found in the intended utterance can serve as stuttering inhibitors. We suggest implementing these innate gestural mirrors to provide immediate and effective amelioration for stuttering.

Speaking with a mirror: engagement of mirror neurons via choral speech and its derivatives induces stuttering inhibition

'Choral speech', 'unison speech', or 'imitation speech' has long been known to immediately induce reflexive, spontaneous, and natural sounding fluency, even the most severe cases of stuttering. Unlike typical post-therapeutic speech, a hallmark characteristic of choral speech is the sense of 'invulnerability' to stuttering, regardless of phonetic context, situational environment, or audience size. We suggest that choral speech immediately inhibits stuttering by engaging mirror systems of neurons, innate primitive neuronal substrates that dominate the initial phases of language development due to their predisposition to reflexively imitate gestural action sequences in a fluent manner. Since mirror systems are primordial in nature, they take precedence over the much later developing stuttering pathology. We suggest that stuttering may best be ameliorated by reengaging mirror neurons via choral speech or one of its derivatives (using digital signal processing technology) to provide gestural mirrors, that are nature's way of immediately overriding the central stuttering block.

Stuttering: a dynamic motor control disorder

The purpose of this review is to determine what neural mechanisms may be dysfunctional in stuttering. Three sources of evidence are reviewed. First, studies of dynamic inter-relationships among brain regions during normal speech and in persons who stutter (PWS) suggest that the timing of neural activity in different regions may be abnormal in PWS. Second, the brain lesions associated with acquired stuttering are reviewed. These indicate that in a high percentage of cases, the primary speech and language regions are not affected but lesions involve other structures, such as the basal ganglia, which may modulate the primary speech and language regions. Third, to characterize the motor control disorder in stuttering, similarities and differences from focal dystonias such as spasmodic dysphonia (SD) and Tourette's syndrome (TS) are reviewed. This review indicates that the central control abnormalities in stuttering are not due to disturbance in one particular brain region but rather a system dysfunction that interferes with rapid and dynamic speech processing for production.

EDUCATIONAL OBJECTIVES

The reader will be able to describe: (1) the similarities and differences between stuttering and other speech motor control disorders, (2) which brain lesions are most likely to produce acquired stuttering in adults, and (3) what type of brain abnormality most likely underlies stuttering.

Pseudofluency in adults who stutter: the illusory outcome of therapy

The majority of therapy programs for people who stutter are aimed at modifying the entire speech output by using techniques that reduce the overt signature events. Use of these techniques for extended time periods are thought to induce true fluency that is automatic, natural, and effortless. It is proposed that the present form of therapeutic intervention induces pseudofluency rather than true fluency. Pseudofluency is the speech posrtherapy of persons who stutter, free of the discrete signature events of stuttering, but replaced by cognitively mediated gestures that are embedded as continuous prolongation or masked stuttering events throughout the speech act. This may account for the high rate of relapse and the problems associated with the maintenance, stability, and naturalness of speech after stuttering therapy.

A common element in the immediate inducement of effortless, natural-sounding, fluent speech in people who stutter: 'the second speech signal'

Recent attempts to find a common element in the inducement of fluent speech have focused on Wingate's notion that fluency can be induced via an altered manner of speaking by placing an emphasis on phonation. The problem with this notion of fluency enhancement is that it appears to be too expansive a scheme of fluency. The schemata allows for any forward flowing speech or speech-like act to be considered fluent despite the increased cognitive mediation, the extra effort involved in implementing the procedure, the unnaturalness of the resultant end product, and a lack of stability over time. It is proposed that the only significant characteristics of 'true fluency' are that it is indistinguishable from the typical fluent speech of people who do not stutter, and that it is effortless in nature. This is achieved via the use of a second speech signal which is not cognitive in nature, is operationally delineated, and is easy to manipulate.

Producing the vowel/a/ prior to speaking inhibits stuttering in adults in the English language

This study investigated the effects of producing and listening to the vowel /a/ on the frequency of overt stuttering moments in eight people who stuttered. Stuttering frequency counts were made for the speech produced in the control condition, and after each of these four experimental conditions: (a) producing a vowel /a/ for 4 s; (b) producing a vowel /a/ for 4 s and waiting for 4 s; (c) listening to a recording of the vowel /a/ for 4 s; and (d) listening to a recording of the vowel /a/ for 4 s and waiting for 4 s. A significant reduction in the stuttering frequency was only observed following production of the vowel /a/ without a 4 s delay (P=0.02), suggesting that the vowel production prior to speech, serves as a temporary fluency enhancer. Its similarity to the occurrence of overt stuttering moments (e.g. discrete part-word repetitions and prolongation's) and its relationship to the fundamental nature of the pathology are discussed.

Stutter-free and stutter-filled speech signals and their role in stuttering amelioration for English speaking adults

This study examined the power of an exogenously generated stuttered speech signal on stuttering frequency when compared to an exogenously generated normal speech signal. In addition, we examined the specific components of the second speech signal, which might be responsible for the inducement of fluency in people who stutter. Eight males and two females who stuttered participated in this study. Experiment I involved meaningful speech: normal continuous speech, normal interrupted speech, stuttered continuous speech, and stuttered interrupted speech, whereas Experiment II involved vowels and consonants: /a/, /a-i-u/, /s/, /s-sh-f/. The results indicated that stuttered and normal speech signals were equally effective in reducing stuttering frequency. Further, the vowels were more powerful than consonants in inducing fluency for people who stutter. It is suggested that acoustic manifestations of stuttering, rather than a problem, may be a natural compensatory mechanism to bypass or inhibit the 'involuntary block' at the neural level.