Both coproduction and the more recent task dynamic models ofspeech production have advanced an explanation for certain kinds of vowel shortening in terms of coarticulatory overlap between neighbouring speech sounds. In this study, the extent to which coarticulatory overlap between opening and closing jaw movement gestures accompanies the accented/unaccented vowel distinction is considered. The authors begin by quantifying the salient differences between truncation, which is caused by a close phasing of articulatory gestures, and linear rescaling of jaw movements. In both truncation and linear rescaling, the duration and amplitude of movement decrease, and the peak velocities remain the same: the main differences occur in the resulting shape of the waveform between the temporal location of the peak velocities in the opening and closing gestures. Three parameters that encode these shape differences are then applied to the speech movements produced by three subjects. This study shows that the accented/unaccented differences are more appropriately modelled as a consequence of truncation, than linear rescaling.