Kinematic redundancies in /u/ production with and without dysarthria

Abstract

The speech sensorimotor control system exploits kinematic redundancies: various articulatory degrees of freedom can exhibit trading relationships in service of a speech goal. These redundancies affect movements within and across articulators, resulting in multiple “motor equivalent” patterns that may lead to perceptually equivalent phonemes. One classic example of this redundancy is the purported trading relationship between the tongue and lips in controlling the frequency of the second formant (F2). For the acoustic goal of achieving a relatively low F2 frequency in the vowel /u/, neurotypical talkers may exhibit trade-offs in tongue dorsum and lip position to allow motor adaptability while achieving the acoustic goal. The current work examines speech kinematic and acoustic data from many talkers with and without dysarthria during connected speech to further evaluate the proposition that tongue-lip movement trade-offs allow relatively adaptable articulatory movement in service of a relatively stable acoustic goal during /u/. It is hypothesized that idiosyncrasies in the kinematic form of tongue-lip trade-offs may reflect speaker-specific articulatory-acoustic mappings and that dysarthria may compromise the use of kinematic redundancies, particularly when articulation is severely impaired. Discussion will focus on how methodological issues, particularly kinematic and acoustic normalization, influence the findings.