Contents lists available at ScienceDirect Displays journal homepage: www.elsevier.com/locate/displa Postural stability predicts the likelihood of cybersickness in active HMD- based virtual reality Benjamin Arcioni a , Stephen Palmisano a, ⁎ , Deborah Apthorp b,c , Juno Kim d a School of Psychology, University of Wollongong, NSW 2522, Australia b School of Psychology and Behavioural Science, Faculty of Health & Medicine, University of New England, NSW 2351, Australia c Research School of Computer Science, College of Engineering & Computer Science, Australian National University, ACT 2601, Australia d School of Optometry and Vision Science, The University of New South Wales, Australia ARTICLE INFO Keywords: Self-motion Optic flow Sickness Virtual reality Head-mounted display ABSTRACT Cybersickness is common during virtual reality experiences with head-mounted displays (HMDs). Previously it has been shown that individual differences in postural activity can predict which people are more likely to experience visually-induced motion sickness. This study examined whether such predictions also generalise to the cybersickness experienced during active HMD-based virtual reality. Multisensory stimulation was generated by having participants continuously turn their heads from left to right while viewing the self-motion simulations. Real-time head tracking was then used to create ecological (‘compensated’) and non-ecological (‘inversely compensated’) head-and-display motion conditions. Ten (out of 20) participants reported feeling sick after being exposed to these self-motion simulations. Cybersickness did not differ significantly between the two compen- sation conditions. However, individual differences in spontaneous postural instability when standing quietly were found to predict the likelihood of subsequently experiencing cybersickness. These findings support recent proposals that postural measures can help diagnose who will benefit the most/least from HMD-based virtual reality. 1. Introduction Head Mounted Displays (HMDs) offer an efficient and cost-effective alternative to other tools used to generate virtual environments for research, training and treatment [1,2]. In recent years, a number of companies have entered the commercial HMD market and are now producing devices ranging widely in cost. These HMDs range from Google Cardboard, which uses a smartphone placed in a cardboard frame, to custom-built headsets such as the Oculus Rift and the HTC Vive. The latter HMDs have wide binocular fields of view (100° or more) and provide stereoscopic 3D content, which can enhance illu- sions of self-motion within the scene [3–7]. The head tracking on these HMDs also allows for real time updates of the user’s viewpoint across a 360° field of view. This can facilitate exploration, increase the per- ceived realism of the simulation, and produce a stronger sense of im- mersion [8]. However, despite the benefits of HMD-based virtual rea- lity, there are still a number of problems associated with HMD use [9]. One commonly reported side-effect of HMDs is that they can induce sickness symptoms similar to those caused by the physical motion of the observer [10]. Common sickness symptoms induced by HMDs include nausea, dizziness, stomach awareness, disorientation and headaches [11]. Reports suggest that these symptoms can last for hours, or in some cases days, after exposure to the virtual environment [10–12]. In the past, the sickness experienced in virtual reality has been described using a variety of terms, including gaming sickness, simulator sickness, and cybersickness [10,13–19]. This study will focus on cybersickness as opposed to visually induced motion sickness (VIMS). While VIMS refers to sickness induced primarily by visual motion stimulation (such as that provided by fixed-base flight and driving simulators), we argue that HMD-based virtual reality instead induces cybersickness, because the provocative motion stimulation might be visual, non-visual or multi- sensory in origin [18,20]. One approach to improve the uptake of HMD-based virtual reality is to find ways to reduce cybersickness in all individuals. While head movements are often required to explore virtual environments when wearing HMDs, the multisensory stimulation they generate appears to increase the likelihood of cybersickness [21,22]. This may explain why users move their heads less when exploring virtual, compared to real world, environments [23]. Thus, we need to better understand the roles that active head-motion and head tracking play in generating HMD- https://doi.org/10.1016/j.displa.2018.07.001 Received 8 January 2018; Received in revised form 23 April 2018; Accepted 3 July 2018 ⁎ Corresponding author. E-mail address: stephenp@uow.edu.au (S. Palmisano). Displays 58 (2019) 3–11 Available online 09 July 2018 0141-9382/ Crown Copyright © 2018 Published by Elsevier B.V. All rights reserved. T