Timing in finger tapping and speech: A comparison between stutterers and fluent speakers

Abstract

Stutterers, even in their fluent utterances, seem to be less able than nonstutterers to time speech motor activity precisely. The question addressed in this study is whether this timing inability is caused by a deficient central timing mechanism or whether it is caused by a more variable motor output process. To this end, twelve adult stutterers and twelve control subjects were asked to perform several variants of a rhythmic keytapping task and a speaking task in which they were asked to utter a vowel or a short word at regular intervals. The results were remarkably similar for both groups. This was true for conditions requiring finger movements, speech movements, or coordination of two simultaneous activities. Only on one measure — the ability to synchronize speech and tapping with a rhytmic tone - did the stutterers show larger variability than the nonstutterers. In contrast to the rhythmic performance, the simultaneous measurements of lip EMGs showed strong group differences. The order of upper lip and lower lip peak EMGs was different in stutterers and in nonstutterers, and the length of the time interval between these EMG peaks was also more variable in stutterers than in nonstutterers. In addition, the duration of lip EMG from peak to acoustic onset was longer in stutterers. It is argued that stutterers do not have a large general timing deficit. Rather, they have coordination disabilities which result in the EMG irregularities.