Functional Data Analysis of Lip Movements: Repetition Variability as a Function of Age

This study examined inter-repetition variability of lip movements across repetitions of the same utterance as a function of age in Swedish speakers. Lip movement data of 15-20 repetitions of a short Swedish phrase from 37 typically developed Swedish children and adults (19 females, 18 males, aged 5-31 years) were collected using threedimensional articulography, and submitted to functional data analysis (FDA), a method for analysing variability in signals. For comparison, we also calculated another metric of variability; the spatiotemporal index (STI). Results showed moderate negative correlations between age and STI as well as the two FDA indices amplitude variability and phase (temporal) variability. Linear regression analysis indicated the largest effect for amplitude variability, and the smallest for phase variability, supporting the potential for factoring out different types of variability for kinetic measurements of lip movements.