Kinematic analysis of lip closure in stutterers' fluent speech.

An analysis of lip and jaw motion was carried out in order to evaluate previous observations on the fluent speech of stutterers and to describe possible effects of speech therapy. A strain gauge system was used to transduce lip and jaw movements during fluent repetitions of "sapapple" in adult stutterers and nonstutterers. Fifteen movement parameters were measured on lip closure for the initial /p/ sound in a group of 10 normal speakers, 10 stutterers who had no recent speech therapy, and 8 stutterers who had been through an intensive speech therapy program involving modification of speech timing. The no-therapy group and nonstutterers did not differ significantly in terms of any movement parameter. Stutterers who had been through speech therapy showed significant increases in jaw movement duration and time to peak velocity of the upper lip, lower lip, and jaw. The expected timing pattern for lip and jaw velocity peaks on lip closure (UL-LL-J) was the most frequently occurring pattern, but deviations from this pattern were observed in both stutterers and nonstutterers. The occurrence of reversals was most prevalent in the therapy group, and it was associated with increases in jaw movement duration across subjects. It is suggested that for the type of movement studied here, anomalies in stutterers' fluent speech are likely to be the result of acquired adjustments rather than properties of the speech neuromotor system that underly dysfluency.