Influence of Utterance Length and Complexity on Trajectory
Stability and Phrase Durations Age Related Changes

N Sadagopan, A Smith


We examined the effects of utterance length and complexity on speech movement stability for 5-, 7-, 9-, 12-, 14- and 16-year old children and young adults (age 20-22-years). The lower-lip movement for the utterance, a short phrase produced in isolation as well as embedded in two longer, more complex sentences was recorded for the 210 participants (15 male and 15 female in each age group). A trajectory variability index was utilized to quantify the reproducibility of movement trajectories across 10 repetitions of the target phrase, and phrase durations were measured for the target utterance in both baseline and embedded conditions in order (1) to determine the developmental course of any effects of length/complexity on speech motor performance, (2) to infer speech motor processing mechanisms for children and adults from the phrase durations for baseline and embedded conditions. For all age groups except young adults, increased length and complexity resulted in significantly decreased speech movement stability. The durations of the phrase in isolation and in the embedded conditions also showed a protracted developmental pattern, which was distinct from that of the variability index. These findings suggest a very protracted time course for the development of speech motor processes and language/motor interactions.