Initial observations concerning developmental characteristics of labio-mandibular kinematics.

Acoustic measurements have shown that children's segment durations are often longer than those of adults. It is unclear from previous research, however, why this occurs. One possibility is that children's less mature peripheral speech mechanisms limit the rate at which they can perform articulatory movements and that this results in longer acoustic segment durations. Another possible cause of children's longer segment durations is that "higher-order," organizational factors might affect their ability to plan and sequence phonetic strings. This too could limit the rate at which they produce speech gestures, thus resulting in longer segment durations. The present study attempted to clarify such issues by obtaining articulatory movement data from four children and three adults using strain gage instrumentation to monitor superior-inferior lip and jaw displacement and velocity. Results indicate that the children tended to move their articulators more slowly than the adults, despite the fact that both groups exhibited comparable articulatory displacements. Differences observed between the adults and children concerning vocal tract size and movement variability indicate that "lower-level," physical factors may be partially involved in children's slower articulatory movements. However, differences between the two groups regarding anticipation of certain articulatory sequences suggest that "higher-order," organizational effects may also be associated with children's slower movements and, therefore, their longer segment durations.