The role of the jaw in rhythming quantity contrasts (VCC v.s. VVC) in Arabic was examined by monitoring vertical displacements, at two rates, for two Tunisians and two Kuweitis. Results show that at conversational rate, contrasts depend on differences in absolute timing along only one time domain: the cycle between two jaw lowering onsets. At fast rate, relative timing values no longer carry quantity contrasts for two speakers (one in each dialect) within this cycle, whereas the contrast is still present in the cycle between two jaw lowering peak velocities for all speakers. For velocity profiles the contrast is at best visible in the jaw closing gesture. VCCs are all asymmetrical at normal rate and the symmetric shape, characteristic of the VVC control is generally adopted at fast rate; except for the VCCs of the two speakers who resisted rate degradation in both cycles.

Keywords: Jaw phasings, velocity profiles, Arabic, quantity contrasts.