Second International Workshop on Models and Analysis of Vocal Emissions for Biomedical Applications (MAVEBA 2001)

Florence, Italy
September 13-15, 2001

Principal Differential Analysis of Lip Motion Signals

Jorge C. Lucero

Department of Mathematics, University of Brasilia, Brasilia, Brazil

Principal differential analysis is applied to lip motion recorded from a subject during the repeated production of the sentence “Buy Bobby a puppy” at fast, normal, and slow rates. In this technique, a second order differential equation of the form D2xi(t) + w1(t)Dxi(t) + w0(t)xi(t) = 0 is fitted to the lip trajectories xi(t). The objective is to characterize lip trajectories at different speaking rates in terms of biomechanical parameters as stiffness, damping, and applied external forces. The results show that, in the case of fast rate, the lip system is substantially underdamped and behaves like a simple mass-spring oscillator. In the case of slow rate, on the other hand, the lips are under a stronger external control to conform to the required trajectory. The case of normal rate falls between the fast and slow rate cases. Further, the variability computed at the forcing level increases with decreasing speaking rate. These results suggest that, at fast speaking rates, the lips are left to move at their natural frequency and so their motion presents low variability across repetitions. At slow rates, on the other hand, a stronger external control is exerted, whose associated variability results in increased variability of the lip motion.

Index Terms. Principal differential analysis; Functional data analysis; Lip motion; Biomechanical modeling; Statistical modeling.

Full Paper

Bibliographic reference.  Lucero, Jorge C. (2001): "Principal differential analysis of lip motion signals", In MAVEBA-2001, 254-259.