Searching For Predictors of Chronic Stuttering

Anne Smith, Ph.D.
Purdue University

From the Stuttering Foundation's 2007 fall newsletter

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I am pleased to have this opportunity to update you on the progress of the Purdue Stuttering Project over the past year. You may recall from my earlier article that we are engaged in a longitudinal study of young children who stutter and their normally fluent controls. With funding from the NIH's National Institute on Deafness and Other Communication Disorders, we have been recruiting 4 and 5-year-olds, and we will be following them yearly for a period of 5 years (that is, if our project is renewed ' money is very tight at NIH these days, so keep your fingers crossed for us!).

In our first year of the longitudinal study, we have tested 34 children who stutter on an extensive set of experimental protocols that includes recording orofacial movements and muscle activity during speech, testing basic timing ability in a hand clapping task, and recording the electrical activity of the brain (EEG) while the children watch a video about a young penguin named 'Pingu.' We have analyzed some of our 'year 1' data, and many exciting results have come to light.

I have space here to describe one of these new findings. We included the clapping task in our protocol, because scientists studying motor behavior have used bimanual hand clapping as a classical way to examine the brain's ability to 'keep time.'

The children are asked to clap their hands in time with a metronome beat. After clapping with the beat for about 15 claps, the beat goes off, and the children are asked to keep clapping until we have about 30 unpaced claps. We ask the kids to do this several times.

Our data analysis consists of analyzing the unpaced claps, so that we can determine (1) if they were faster or slower than the target rate they were trying to maintain, and (2) how variable they were in keeping up this rate. So far, we have analyzed data from 17 children who stutter (CWS) and 13 children who are normally developing (CND).

What we have found is that the CWS and the CND have the same average rate of clapping; both groups tend to speed up when the beat goes off. Concerning the variability of their clapping, we compute a statistic that reflects their variability in percent.

The range of variability in percent for the normally developing children was 5 to 13%. Interestingly, 10 of the 17 CWS had variability percentages outside the range of the CND. These 10 CWS had greater variability percentages than any of the CND, and these ranged from 15 to 32%! From these early analyses, we conclude that about 60% of 4 and 5-year-olds who are stuttering are unusually poor at keeping time compared to their normally developing peers.

One overall goal of the project is to be able to predict which of the children who are stuttering are most likely to develop a chronic stuttering problem. Are these children who are poor at a basic timing task at greater risk for chronic stuttering? Is this a sign that their young brains have motor timing circuitry that is developing atypically?

These are some of the questions we hope to be able to answer after following these children for five years. I look forward to updating you again in the future as more of our experiments reveal more about the physiological characteristics of these stuttering children.