Nora Pourhashemi¹, Kayton Jaksic^1,2, Behrang Keshavarz^3,4, Taylor W. Cleworth^1,2; ¹York University, ²Centre for Vision Research, ³Toronto Metropolitan University, ⁴KITE-Toronto Rehabilitation Institute

BACKGROUND: Vision provides essential sensory feedback for upright stance. Delayed visual feedback can affect postural control by creating a mismatch between one’s motor actions and visual responses. There is limited work examining the relationship between visual delay, postural responses, and visually induced motion sickness (VIMS) during dynamic balance tasks. This study examined the effects of delayed visual feedback on dynamic postural control and VIMS among healthy individuals. METHODS: Twenty young adults stood on a force plate mounted to a motorized platform that continuously translated in the anteroposterior (AP) direction for 60s while wearing a virtual reality head-mounted display (HTC Vive). Full body kinematics using motion capture (Vicon) and center of pressure (COP) displacements were collected. Surface electromyography (EMG) was recorded from the right medial gastrocnemius (MGast), tibialis anterior (TA) and soleus (Sol) muscles. Trials for each delay condition (0ms, 250ms, 500ms) were randomized, and repeated once. Following each trial, questionnaires were completed to assess perceived stability and VIMS. AP and mediolateral (ML) root mean square (RMS), and sample entropy (SE) were used to quantify postural responses. Mean activity and co-contraction between antagonistic muscles were calculated from EMG data. RESULTS: As the amount of delay increased, AP and ML COP RMS, AP COP SE, as well as AP Head and Trunk RMS significantly increased. TA and MGast activity and TA/SOL co-contraction were significantly greater with increased visual delay. Perceived stability significantly decreased, while VIMS remained unaffected with increased delayed visual feedback. During repeated exposure, perceived stability increased, while postural responses decreased. CONCLUSIONS: Overall, increasing the delay between head motion and visual feedback during a dynamic balance task resulted in larger postural responses but did not affect VIMS. However, upon repeated exposure, postural responses decreased. Therefore, participants demonstrated adaptability, integral for developing interventions aimed to reduce fall risk and balance deficits.

Acknowledgements: Funded by Natural Sciences and Engineering Research Council of Canada (NSERC) and Vision: Science to Applications (VISTA) at York University.