Leg movements affect speech intensity.

Coordination between speech acoustics and manual gestures has been conceived as "not biologically mandated" (McClave E. 27(1): 69-89, 1998). However, recent work suggests a biomechanical entanglement between the upper limbs and the respiratory-vocal system (Pouw W, de Jonge-Hoekstra D, Harrison SJ, Paxton A, Dixon JA. 1491(1): 89-105, 2021). Pouw et al. found that for movements with a high physical impulse, speech acoustics co-occur with the physical impulses of upper limb movements. They interpret this result in terms of biomechanical coupling between arm motion and speech via the breathing system. This coupling could support the synchrony observed between speech prosody and arm gestures during communication. The present study investigates whether the effect of physical impulse on speech acoustics can be extended to leg motion, assumed to be controlled independently from oral communication. The study involved 25 native speakers of German who recalled short stories while biking with their arms or their legs. These conditions were compared with a static condition in which participants could not move their arms. Our analyses are similar to that of Pouw et al. (Pouw W, de Jonge-Hoekstra D, Harrison SJ, Paxton A, Dixon JA. 1491(1): 89-105, 2021). Results reveal that the presence of intensity peaks in the acoustic signal co-occur with the time of peak acceleration of legs' biking movements. However, this was not observed when biking with the arms, which corresponded to lower acceleration peaks. In contrast to intensity, F0 was not affected in the arm and leg conditions. These results suggest that ) the biomechanical entanglements between the respiratory-vocal system and the lower limbs may also impact speech; ) the physical impulse may have to reach a threshold to impact speech acoustics. The link between speech and limb motion is an interdisciplinary challenge and a core issue in motor control and language research. Our research aims to disentangle the potential biomechanical links between lower limbs and the speech apparatus, by investigating the effect of leg movements on speech acoustics.