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Among the more than 150 interesting symposia at AAAS 2011, Section Z (Linguistics) sponsored five. I posted earlier about the symposium on "What Bilinguals Tell Us About Mind and Brain". I'm adding a link today to another one, "From Freud to fMRI: Untangling the Mystery of Stuttering". Its abstract:

This symposium will track current developments in the study of stuttering, the fruit of recent collaborations among researchers in the fields of genetics, speech motor control, and language processing. Until the past decade, much of the research into this common yet poorly understood communication disorder tended to be narrowly focused on accounts within a single discipline, from psychoanalysis to learning theory to articulatory control to hemispheric asymmetry. In this symposium, we will provide examples of the cross-disciplinary research that is changing consensus on the probable basis for stuttering. Recent advances in genetics, brain imaging, and speech motor control will be discussed in terms of their ramifications for better understanding this elusive disorder as well as treating it more effectively.

And I'll assert again that the AAAS would do itself and (more important) its mission a service by putting slides and videos or audios of these symposia on the web, for free public access. I was happy to learn from Stephen Anderson that steps of this kind are now under consideration.

The contributions to this symposium, with their abstracts, are listed below.

Dennis Drayna, National Institutes on Deafness and Other Communication Disorders, "Identifying the Genetic Contributions to Stuttering":

The first speaker will summarize how studies on genetic factors in stuttering have led to the first understanding of the causes of the disorder at the molecular level. This portion of the symposium will also discuss how additional chromosomal loci may identify additional molecular deficits that cause stuttering, and also relate stuttering to other human communication disorders.

Luc de Nil, University of Toronto, "Brain Anatomy and Function in People Who Stutter":

This portion of the session will integrate recent findings in the neuroimaging literature. In particular, the speaker will discuss how a substantial number of findings differentiate children and adults who stutter from typically fluent speakers with respect to brain morphology as well as functional speech/language and motor processes. These findings help to elucidate the possible deficits that contribute to the development and persistence of stuttering. Importantly, it is also evident that many of these patterns are responsive to therapeutic intervention, suggesting that some aspects of these neurological profiles are plastic and amenable to behavioral treatment.

Anne Smith, Purdue University, "How Stuttering Emerges from the Interfaces Between Linguistic and Motor Processing":

The third speaker will demonstrate how diverse findings of speech-motor learning and control deficits in people who stutter can be integrated with a companion literature that proposes a more central deficit in speech-language processing. She will present recent findings showing that language planning in people who stutter uniquely destabilizes speech motor control, a finding made possible by viewing stuttering through an interdisciplinary lens. She will conclude with discussion of how our understanding of the nature and most efficient treatment of stuttering can be further advanced through integration of additional disciplinary approaches.

Under the current arrangements, that's all the information that the AAAS offers about the session. (Well, you could write off for an audio CD of the presentations; but I doubt that many people will do so, or for that matter that they'll be able to get much value from the audio without the slides.)

However, as usual, you could use Google Scholar to find recent publications by Dennis Drayna, Luc de Nil, and Anne Smith on this topic. You would turn up, for example, Lindsey Olander, Anne Smith, and Howard N. Zelaznik, "Evidence That a Motor Timing Deficit Is a Factor in the Development of Stuttering", Journal of Speech, Language, and Hearing Research, 53:876-886 August 2010. The abstract:

Purpose: To determine whether young children who stutter have a basic motor timing and/or a coordination deficit.

Method: Between-hands coordination and variability of rhythmic motor timing were assessed in 17 children who stutter (4–6 years of age) and 13 age-matched controls. Children clapped in rhythm with a metronome with a 600-ms interbeat interval and then attempted to continue to match this target rate for 32 unpaced claps.

Results: Children who stutter did not significantly differ from children who were typically developing on mean clapping rate or number of usable trials produced; however, they produced remarkably higher variability levels of interclap interval. Of particular interest was the bimodal distribution of the stuttering children on clapping variability. One subgroup of children who stutter clustered within the normal range, but 60% of the children who stutter exhibited timing variability that was greater than the poorest performing nonstuttering child. Children who stutter were not more variable in measures of coordination between the 2 hands (mean and median phase difference between hands).

Conclusion: We infer that there is a subgroup of young stuttering children who exhibit a nonspeech motor timing deficit, and we discuss this result as it pertains to recovery or persistence of stuttering.

Here's a figure that illustrates the lack of difference in mean clapping rate:

And here's an illustration of the differences in clapping variability:

The authors observe that

These results provide clear evidence that in its early years, developmental stuttering is associated with a fundamental deficit in the child's ability to generate consistent, rhythmic motor behaviors. This suggests that children who stutter have atypical development of neural networks in the brain involved in the control of speech and other complex movements.

The reference to "developmental stuttering" raises an intriguing possibility, which they discuss as follows:

An intriguing speculation arising from the present work is that the presence of a general motor timing deficit in children who stutter may be an early indicator of persistent stuttering. In other words, children who stutter who do not show evidence of a general timing deficit might spontaneously recover, whereas those who do show abnormally high motor timing variability will persist. Currently there is no way to determine whether a child who stutters will continue to do so into adulthood. Findings of the Illinois Stuttering Project (Ambrose & Yairi, 1999; Paden, Yairi, & Ambrose, 1999; Watkins, Yairi, & Ambrose, 1999; Yairi & Ambrose, 1999)—a 4-year longitudinal study of children who stuttered—revealed a 75% spontaneous recovery rate for 3-year-olds who stuttered. Because the children in the current study were 4-, 5-, and 6-year-olds, and as a result had already been stuttering for 1–3 years, recovery rates for this group should be approximately 50%. The distribution of clapping variability levels produced by children who stutter in the present study (41% of the children who stuttered falling within the range produced by typically developing children, and 59% producing higher variability levels than children who stuttered) roughly matches expected recovery rates.

Although it is beyond the scope of the present study to strongly suggest that clapping variability is an early marker of stuttering persistence versus recovery, the bimodal-looking distribution in the coefficient of variation in the children who stuttered provides a promising possibility for the early identification of persistent stuttering and will continue to be investigated in future work in our laboratory. A procedure for the early detection of persistent stuttering would clearly be beneficial for speech language pathologists and families of children who stutter when deciding whether a young child who is stuttering should enter therapy.

I've long wondered whether machine-learning methods applied to detailed speech-timing measures might be able to predict which cases of developmental stuttering would "grow out of it" and which would not. But if something as simply as clapping variability could accomplish such a prediction, that would be wonderful. And perhaps the results of a set of simple quantitative measures, of which this might be one, would do even better.

This is a significant problem, worth some focused effort to solve, since the incidence of developmental stuttering is apparently in the range of 5-10%. The problem disappears without intervention in most of the children who are affected; and (in addition to possible waste of time and money) there is some concern that early intervention might make the problem worse in some cases, by making sufferers anxious about the problem. On the other hand, persistent stuttering can be improved by therapy, and apparently in this case earlier intervention is better.

For some indication of the state of controversy in this field, see Peter Howell, "Listen to the Lessons of The King's Speech", Nature 470 2/2/2011; and a response by Mark Onslow and Ann Packman, "Stuttering studies support treatment", Nature 470 2/24/2011.

March 9, 2011 @ 8:24 am · Filed by Mark Liberman under Psychology of language

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