Vocal effort, coordination, and balance

Abstract

Manipulating speaking and discourse requirements allows us to asses the time-varying correspondences between various subsystems within a talker at different levels of vocal effort. These subsystems include fundamental frequency (F0) and acoustic amplitude, rigid body (6D) motion of the head, motion (2D) of the body, and postural forces and torques measured at the feet. Analysis of six speakers has confirmed our hypothesis that as vocal effort increases coordination among sub-systems simplifies, as shown by greater correspondence (e.g., the instantaneous correlation) between the various time-series measures. However, at the two highest levels of vocal effort, elicited by having talkers shout to and yell at someone located appropriately far away, elements of the postural force, notably one or more torque components, often show a reduction in correspondence with the other measures. We interpret this result as evidence that talkers become more rigidly coordinated at the highest levels of vocal effort, which can interfere with their balance. Furthermore, the discourse type—shouting at someone to carry on a conversation vs. yelling at someone not expected to reply—can be associated with differing amounts of imbalance.