Supporting scientific references

People who stutter exhibit suboptimal sensorimotor control of the speech articulators; visual feedback can improve their performance.
De Nil, L. F., & Abbs, J. H. (1991). Kinaesthetic acuity of stutterers and nonstutterers for oral and non-oral movements. Brain, 114, 2145–2158

Fluency improves with articulatory slowing and hyperarticulation; increasing feedback (proprioceptive, visual, auditory) stabilizes the sensorimotor system.
Namasivayam, A. K., & van Lieshout, P. (2011). Speech motor skill and stuttering. Journal of Motor Behavior, 43(6), 477–489

Because people who stutter show smaller gains and poorer coordination than typically fluent speakers—and have more difficulty with generalization and maintenance—motor training promotes responses with shorter temporal latency and greater accuracy.
Namasivayam, A. K., van Lieshout, P. & De Nil, L. F. (2008 ). Bite block perturbation in people who stutter: immediate compensatory and delayed adaptive processes. Journal of communication disorders, 41, 4, 372-394
Smits-Bandstra S e De Nil, L. F. (2007) Sequence skill learning in persons who stutter: implications for CSTC dysfunctions, Journal of fluency disorders, 32, 4, 251-278

People who stutter exhibit sensorimotor control deficits rooted in internal–external auditory feedback processing. The use of supplementary external feedback can improve fluency.
Namasivayam, A. K., van Lieshout, P., McIlroy, W. E., & De Nil, L. F. (2009). Sensory feedback dependence hypothesis in persons who stutter. Human Movement Science, 28(6), 688–707
Van Lieshout, P., Hulstijn, W., & Peters, H. F. M. (2004). Searching for the weak link in the speech production chain of people who stutter. In B. Maassen, R. D. Kent, H. F. M. Peters, P. H. H. M. van Lieshout, & W. E. Hulstijn (Eds.), Speech motor control in normal and disordered speech (pp. 313–356). Oxford, UK: Oxford University Press

Acoustic studies show that people who stutter—even during fluent speech—exhibit longer vowel durations, slower consonant–vowel transitions, and delayed onset of voicing for voiced consonants. Consequently, slowing the syllabic rate may facilitate fluency.
Colcord, R. D., & Adams, M. R. (1979). Voicing duration and vocal SLP changes associated with stuttering reduction during singing. Journal of Speech and Hearing Research, 22, 468–479

DiSimoni, F. G. (1974). Preliminary study of certain timing relationships in the speech of stutterers. Journal of the Acoustical Society of America, 56, 695–696
Hillman, R. E., & Gilbert, H. R. (1977). Voice onset time for voiceless stop consonants in the fluent reading of stutterers and nonstutterers. Journal of the Acoustical Society of America, 61, 610–611
Starkweather, C. W., & Myers, M. (1979). Duration of subsegments within the intervocalic interval in stutterers stutterers and nonstutterers. Journal of Fluency Disorders, 4, 205–214

The findings from acoustic studies are corroborated by kinematic investigations. Consequently, slowing the syllabic rate may facilitate fluency.
Alfonso, P. J., Story, R. S., & Watson, B. C. (1987). The organization of supralaryngeal articulation in stutterers’ fluent speech production: A second report. Annual Bulletin Research Institute of Logopedics and Phoniatrics, 21, 117–129
Zimmermann, G. N. (1980). Articulatory dynamics of fluent utterances of stutterers and nonstutterers. Journal of Speech and Hearing Research, 23, 95–107

People who stutter have reduced central capacity to evaluate the relationships between efferent and afferent signals during speech; as a result, they take longer (i.e., are slower) or expend more resources—at the expense of other functions—to perform this evaluation. Consequently, slowing the syllabic rate may facilitate fluency by enabling the allocation of the necessary processing resources.
Andrews G, Craig, A, Feyer, A, Hoddinott, S, Howie P, Neilson M (1983) Stuttering: a review of research findings and theories circa 1982, Journal of speech and hearing disorders, 48, 226-245
Neilson, M. D., & Neilson, P. D. (1985). Speech motor control and stuttering. In DG Russell e B. Abernathy, Motor. Memory and control, 68-80, Dunedin New Zealand: Human Performance Associates
Neilson, M. D., & Neilson, P. D. (1987). Speech motor control and stuttering: A computational model of adaptive sensory-motor processing. Speech Communication, 6, 325–333
Neilson, M. D., & Neilson, P. D. (2000). A computational theory of motor synergy development: implications for stuttering. Journal of fluency disorders, 25, 171 (Special edition Abstract of the Third World Congress on Fluency Disorders, Nyborg, Denmark)

Phonological encoding is inherently slower in people who stutter, and phonological errors arise due to competition among multiple phonemes. In attempts at online correction, blocks (with increased muscular tension), repetitions, and prolongations are generated. People who stutter benefit from reducing the syllabic rate, as it provides more time for phonological encoding, given that the locus of error is phonological rather than semantic, lexical, or syntactic.
Postma A, Kolk H. (1993) The covert repair hypothesis: prearticulatory repair processes in normal and stuttered disfluencies, J Speech Hear Res, Jun: 36, 472-87

From a resource-allocation perspective, a person who stutters—struggling to plan and/or produce fluent speech in order to overcome frequent breakdowns—overuses limited executive-function resources, including attentional control, to compensate for the dysregulation of otherwise automatic, fluency-supporting processes.
Anderson JD, Ofoe LC. (2019) The role of executive function in developmental stuttering. Semin Speech Lang, 40(4): 305-319
Singer CM, Walden TA, Jones RM. (2020) Attention, speech-language dissociations and stuttering chronicity. American Journal of speech-language Pathology; Rockville 29,I: 157-167
Ofoe LC, Anderson, JD, Nitourou K. (2018) Short-term memory, inhibition and attention in developmental stuttering: a meta-analysis. Journal of speech, language an hearing research; Rockville, 61,VII: 1626-1648

There are stuttering rehabilitation techniques based on dual-task paradigms—e.g., choral reading and regulatory gestures, long regarded as “distractors.” Several studies suggest that concurrent tasks can induce fluency gains for the following reasons:
Distraction from the constructed speaking style. Individuals are diverted from their habitual, overly controlled way of speaking, allowing more automatic speech. The improvement would thus be attributable to attentional redistribution and reduced executive control over verbal execution; the heightened attentional alert state, which is detrimental to fluency, is mitigated.
Reduction of anticipatory anxiety. Lower anticipatory anxiety decreases attention devoted to self-monitoring, thereby reducing disfluencies.
Hierarchical–modular organization hypothesis. Under a hierarchical/modular control model, a second task may improve performance because the additional attentional demand required to coordinate multiple activities concurrently leads to better overall coordination and thus improved fluency.
Arends N., Povel D. J., Kolk H. (1988), “Stuttering as an attentional phenomenon”, Journal of Fluency Disorders, 13, 141-151
Bajaj A. (2007), “Working memory involvement in stuttering: Exploring the evidence and research implications”, Journal of Fluency Disorders, 32, 218-238
Vasic N., Wijnen F. (2005), “Stuttering as a monitoring deficit”, in Hartsuiker R. J., Bastiaanse R., Postma A., Wijnen F. (eds.),Phonological Encoding and Monitoring in Normal and Pathological Speech, Hove, Psychology Press
D’Ambrosio M. (2014). “Balbuzie e attività autonomica: il biofeedback training”, I Care, 39(1), 19-23
D’Ambrosio M., Bracco F., Benso F. (2014), “Assessing fluency in persons with stuttering by complex automatized and non-automatized dual-task conditions”, in M. Cruciani, A. Rega (a cura di), “Corpi, Strumenti e Cognizione. Atti del XI Convegno Annuale dell’Associazione Italiana di Scienze Cognitive”, NEAScience, 1(5), 104-108
D’Ambrosio M., Bracco F., Benso F. (2016), “Misurazioni di fluenza in persone con balbuzie in doppi compiti complessi automatizzati e non automatizzati”, Sistemi Intelligenti, 28(1), 81-101

Nejati V, Pouretemad HR, Bahrami H. (2013) Attention training in rehabilitation of children with developmental stuttering. 32 (2): 297-303

Activation of the right frontal operculum and right insula in people who stutter

Regions involved in:

• Melodic–prosodic perception and production
• Control of the suprasegmental components of speech
• Temporal estimation/judgment tasks
• Attention-demanding tasks (B)
• Phonologically complex, non-repetitive verbal tasks

Bilateral hypoactivation of the auditory cortices

The dysfunction pertains to self-monitoring during speech—specifically, the synchronization and integration of parallel processes initiated to produce an utterance, including the selection of appropriate linguistic components and their motor execution.

Basal ganglia dysfunction

The striatum plays a role (B) in motor learning (procedural memory) and in (B) behaviors governed by reinforcement and punishment, with strong involvement of the dopaminergic system—specifically the balance between D1 and D2 receptors.
Techniques focusing on voice onset, coarticulation, speech rate, and pausing—aimed at increasing inter-syllabic transition times (B)—appear most appropriate for strengthening left-hemisphere control of the temporal/segmental aspects of speech.
At the same time, because these techniques also engage proprioception, they facilitate synchronization (B) by compensating for deficits in the cortico-striato-thalamo-cortical (CSTC) circuit, de-automating movement, and increasing task-focused attention via a dual-task paradigm (B).
Therapies that substitute for or augment deficient sensory information can promote synchrony in the motor commands underlying speech production (B).
Brown S, Ingham R, Ingham JC, Laird AR, Fox PT (2005). Stuttered and fluent speech production: an ALE meta-analysis of functional neuroimaging studies. Hum Brain Mapp 25(1):105-17
Budde KS, Barron DS, Fox PT. (2014) Stuttering, induced fluency, and natural fluency: A hierarchical series of activation likelihood estimation meta-analyses. Brain and Language Volume 139, Pages 99-107
Etchell AC, Civier O, Ballard KJ, Sowman PF. (2018). A systematic literature review of neuroimaging research on developmental stuttering between 1995 and 2016. Journal of fluency disorders, 55; 6-45

Motor Learning – Biofeedback

Augmented feedback – external focus – implicit (non-intentional) learning – desirable difficulties – variable practice.
Schmidt RA, Lee TD. (1999) Motor control and learning, USA: Human Kinetics
Shea CH, Wulf G. (1999) Enhancing motor learning through external-focus instructions and feedback. Hun Mov Sci; 18: 553-571
Graf P, Schacter DL (1985). Implicit and explicit memory for new associates in normal and Amnesic Subjects. J Expo Psychol: Lear Mem Cogn, 11: 5012-518
Cole KJ, Abbs JH (1983). Intentional responses to Kinestesthesic stimuli in orofacial muscles: implications for the coordination of speech movements. J Neurosci 3: 2660-2669
Adams Ja. (1987) Historical review and appraisal of research on the learning, retention and transfer of human motor skills. Psychol Bull, 101: 41-74
Mc Cracken. HD, Stelmach GE. (1977) A test of the schema theory of discrete motor learning. J Mot Behav 9: 193-201
Schmidt R (1975). A schema theory of discrete motor skill learning. Psychol Rev 82:225-260
Magill RA, Hall KG (1990) A review. Of the contextual interference effect in motor skill acquisition. Hun Science, ): 241-289

Regarding the effectiveness of rate reduction, gentle onset, and planned pausing.
Webster RL (1974) A behavioral analysis of stuttering: treatment and Theory. In KS Calhoun e al (Eds). Innovative treatment methods in psychopathology . New York, NY: Wiley
Webster RL (1979). Empirical consideration regarding stuttering therapy. In HH Gregory (Ed) Controversies about stuttering therapy, 209-240. Baltimore, MD: University Park Press
Von Gudenberg AW (2006). Kassel stuttering therapy: evaluation of a computer-aided therapy (German). Forum Logopedie, 20, 6-11
Ryan, B.P. (2006). Gradual Increase in Length and Complexity of Utterance (GILCU). Obtained on November 30, 2006 from: http://www.mnsu.edu/comdis/kuster/TherapyWWW/gilcu.html

Natural fluency. To hear, think, and speak normally.

Regular, smooth speech with only sporadic disfluencies. Speech appears to flow with little effort; the individual does not attend to how they speak or to managing fluency.

• A realistic goal in the preschool years.
• Not a realistic goal at later ages (i.e., a definitive cure of both overt and covert symptoms). There are limits to the extent to which speech-language therapy can modify underlying psychological and biochemical structures and processes, although evidence indicates it can alter brain function.

Superfluency, or controlled fluency. Speech production that is normal or near-normal, but achieved at the cost of increased patient effort.

Few disfluencies are present. The patient pays a cost in terms of attention and self-management of disfluent moments (which the listener perceives), distracting them from content. Depending on the ability to coordinate respiration, phonation, and articulation, this type of fluency may be experienced as unstable. It resembles the speech of a typically fluent speaker under emotional or communicative stress; it is a demanding, multitasking effort—replacing one abnormality with another.

The importance of cognitive-behavioral therapy in stutterig

Stuttering, in addition to impairing speech fluency, can have a range of negative psychosocial consequences for those affected, which may lead to intense anxiety as well as other symptoms. It is therefore essential to include multiple dimensions in a holistic treatment for stuttering. Cognitive-behavioral therapy (CBT) and mindfulness equip patients with skills to manage problems that arise as a consequence of stuttering. Negative associations with stuttering often lead to social anxiety. Accordingly, it is crucial to incorporate treatment methods that address negative attitudes and avoidance related to stuttering. Common CBT components for anxiety management include cognitive restructuring (analyzing cognitive errors and implementing appropriate corrective strategies), attentional training (developing the ability to be aware of—and regulate—where attention is focused), and behavioral experiments (including strategies for approaching social situations linked to negative associations with stuttering).
Mongia, M., Gupta, A. K., Vijay, A., & Sadhu, R. (2019). Management of stuttering using cognitive behavior therapy and mindfulness meditation. Industrial psychiatry journal

Cognitive-behavioral strategies can be effective in reducing stuttering severity by decreasing dysfunctional attitudes and improving assertiveness and quality of life in individuals who stutter.
Reddy, R. P., Sharma, M. P., & N, S. (2010). Cognitive behavior therapy for stuttering: a case series. Indian journal of psychological medicine, 32(1), 49-53.

CBT appears to reduce social avoidance and anxiety and to increase engagement in everyday life.
Menzies, R. G., Onslow, M., Packman, A., & O’Brian, S. (2009). Cognitive behavior therapy for adults who stutter: A tutorial for speech-language pathologists. Journal of fluency disorders, 34(3), 187-200.