Velocity profiles of lip protrusion across changes in speaking rate.

The effects of speaking rate manipulation were examined in the velocity profiles of anticipatory lip protrusion gestures. Systematic changes in the shape, symmetry, and smoothness of the velocity profiles were observed as speaking rate was modulated across a wide range of self-selected rates, from fast to slow. Velocity profiles of movements produced at slower than normal speaking rates demonstrated greater asymmetry, irregularity, and differences in geometric form, compared to a normal and faster-than-normal rates. Subjects evidenced both inter- and intrasubject variability in the accomplishment of lip protrusion and rate manipulations. These results indicate that the velocity profiles of lip protrusion gestures do not necessarily remain invariant across changes in speaking rate. Rather, the data suggest that distinct movement patterns may be generated for slow speaking rates, with select characteristics of the movement pattern being maintained across normal and fast speaking rates.