Evidence that a motor timing deficit is a factor in the development of stuttering

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.

Figure 1

Displacements of each hand from the mid-line during the clapping task. The top line represents the left hand and the bottom line represents the right hand. The circles (for the left hand) and the squares (for the right hand) represent the starting/ending points of each clapping cycle. The top record was unusable, because the child stopped for over 2 seconds. The bottom record shows a trial that was usable.

Figure 2

Graphs of mean inter-clap interval for each child’s right and left hand (top plot) and the coefficient of variation of the inter-clap interval computed for each child’s right and left hand (lower plot).