Lexical frequency co-determines the speed-curvature relation in articulation. (May 2018)

• Record Type: Journal Article
• Authors: Tomaschek, Fabian; Arnold, Denis; Bröker, Franziska; Baayen, R. Harald
• Is Part Of: Journal of phonetics. Volume 68(2018)
• Page Start: 103
• Page End: 116
• Publication Date: 2018-05
• Subjects: Speed-curvature relation -- Lexical frequency -- Electromagnetic articulography -- Speech production -- 1/3 power law; Phonetics -- Periodicals; Phonetics -- Periodicals; Phonétique -- Périodiques; Phonetics; Periodicals; Electronic journals; 414.05
• DOI: 10.1016/j.wocn.2018.02.003
• Languages: English
• ISSNs: 0095-4470

Abstract

Highlights: Tongue movements showed non-linear relation between speed and curvature. Increasing word frequency correlates with smoother articulatory trajectories. Increasing frequency correlates with faster articulatory velocities in tight curves. Speed-curvature relation is modeled by Mandelbrot's rank-frequency equation. Abstract: The relation between speed and curvature provides a characterization of the spatio-temporal orchestration of kinematic movements. For hand movements, this relation has been reported to follow a power law with exponent - 1 / 3 . The same power law has been claimed to govern articulatory movements. We studied the functional form of speed as predicted by curvature using electromagnetic articulography, focusing on three sensors: the tongue tip, the tongue body, and the lower lip. Of specific interest to us was the question of whether the speed-curvature relation is modified by articulatory practice, gauged with words' frequencies of occurrence. Although analyses imposing linearity a priori indeed supported a power law, relaxation of this linearity assumption revealed that the effect of curvature on speed levels off substantially for lower values of curvature. A modification of the power law is proposed that takes this curvature into account. Furthermore, controlling statistically for number of phones and word duration, we observed that the speed-curvature function was further modulated by an interaction of lexical frequency by curvature, such that for increasing frequency, speed decreased slightly for low curvatures while it increased slightly for high curvatures. The modulation of the balance between speed and curvature by lexical frequency provides further evidence that the skill of articulation improves with practice on a word-to-word basis, and challenges theories of speech production.