Visual Perception of Gravity: Effect on Speech Tongue Posture

Abstract

Visual perception of gravity change may impact tongue posture during speech production. Previous studies [Chander et al., 2019, Behav. Sci., 9(11)] report anticipatory visual disturbances inducing compensatory postural behavior in the human body [Philips et al., 2022, Theor. Iss. Ergon. Sci., 23, 25] and, furthermore, showed the magnitude of such postural responses is dependent on velocity and direction of visual perception. Assländer et al. [2023, Sci. Rep., 13, 2594] investigated the visual component impact on body posture balance in virtual reality (VR). An earlier VR study on tongue posture [Chernets et al., 2024, JASA 156] found that posture significantly differed between visually perceived falling vs. rising, and levelled vs. rising gravitational conditions; however, there was inter-participant variation in the direction of tongue posture change with no generalizable consistent directional change across participants. The current study investigates tongue posture in speech production during perceived gravity changes in an immersive VR environment. Ultrasound imaging is used to measure tongue posture changes during speech production compared to a non-speech condition while experiencing a VR plank-walk in gravitationally stable and falling conditions. Furthermore, within the falling condition posture is separated into weightless falling (initial and midpoint of fall) vs. force of fall (endpoint of fall). Acoustic analyses compare the production of an elongated vowel, nonsense CVC sequences, and CVC word sequences across conditions. We predict that the falling condition will induce postural adjustment for vowels, resulting in different tongue postures between the falling and level conditions. Results will be presented for a post-trial immersion questionnaire investigating a possible correlation between reported level of VR immersion and degree of tongue posture compensation, as well as for acoustic and articulatory analyses. Implications for postural adaptation in VR and real environments will be discussed.