The direction of postural threat alters balance control when standing at virtual elevation

Abstract

Anxiogenic settings lead to reduced postural sway while standing, but anxiety-related balance may be influenced by the location of postural threat in the environment. We predicted that the direction of threat would elicit a parallel controlled manifold relative to the standing surface, and an orthogonal uncontrolled manifold during standing. Altogether, 14 healthy participants (8 women, mean age = 27.5 years, SD = 8.2) wore a virtual reality (VR) headset and stood on a matched real-world walkway (2 m × 40 cm × 2 cm) for 30 s at ground level and simulated heights (elevated 15 m) in two positions: (1) parallel to walkway, lateral threat; and (2) perpendicular to walkway, anteroposterior threat. Inertial sensors measured postural sway acceleration (e.g., 95% ellipse, root mean square (RMS) of acceleration), and a wrist-worn monitor measured heart rate coefficient of variation (HR CV). Fully factorial linear-mixed effect regressions (LMER) determined the effects of height and position. HR CV moderately increased from low to high height (p = 0.050, g = 0.397

The Effects of Virtual Height Exposure on Postural Control and Psychophysiological Stress Are Moderated by Individual Height Intolerance

“…Thus, the increased body sway velocity in high fear participants suggests that they may not be able to use sensory feedback adequately when exposed to heights. We also observed that the magnitude of body sway decreased with ascending virtual height (similarly in both groups), which is in line with some of the previous reports ( Cleworth et al, 2012 ; Raffegeau et al, 2020 ), but not others ( Simeonov et al, 2005 ; Wuehr et al, 2019 ; Chander et al, 2021 ). The reasons for such inconsistent findings across the studies are not clear.…”

“…Second, also inconsistent are the reports on the effect of virtual height exposure on postural balance. While Cleworth et al (2012) found that body sway magnitude decreased during exposure to height in VR, several other studies reported the opposite effect, i.e., an increase in the magnitude of body sway (Wuehr et al, 2019;Raffegeau et al, 2020;Chander et al, 2021). Furthermore, it has been reported that postural reactions to simulated height are independent of individual height intolerance and the elicited fear (Wuehr et al, 2019), in contrast to real height exposure when postural adjustments were related to individual fear and anxiety levels (Davis et al, 2009).…”

“…First, considering the psychological effects of virtual height exposure and their relationship to individual differences in visual height intolerance, the results are rather inconsistent regarding the stress-related activation of the ANS. For instance, it has been reported that exposure to height in VR increased heart rate (HR; Diemer et al, 2016 ), had no effect on HR ( Raffegeau et al, 2020 ), or decreased HR ( Simeonov et al, 2005 ), increased electrodermal activity (EDA; Simeonov et al, 2005 ; Cleworth et al, 2012 ; Diemer et al, 2016 ), or did not affect EDA ( Peterson et al, 2018 ; Vermehren and Carpenter, 2020 ), casting doubts on the efficacy of VR simulation to induce a significant sympathetic arousal. In particular, Diemer et al (2016) reported that virtual height exposure elevated HR and EDA also in subjects who did not suffer from fear of heights, whereas in the study by Wuehr et al (2019) HR or EDA were not elevated, even in participants who reported high levels of visual height intolerance.…”

“…Since exposure to height is a natural threat, we expected both groups to show an increase in psychophysiological arousal as well as changes in body sway magnitude and velocity indicative of increased body stiffening ( Adkin et al, 2000 ; Carpenter et al, 2001 ; Davis et al, 2009 ; Huffman et al, 2009 ; Cleworth et al, 2012 ). Postural stiffening is a protective motor reaction that prevents destabilisation from perturbations and is characterised by lower amplitude but higher frequency of body sway, especially in the direction of postural threat ( Carpenter et al, 2001 ; Raffegeau et al, 2020 ). However, due to higher sensitivity of individuals with high levels of fear, we expected more intense psychophysiological response and impaired balance control in the high compared with the low fear group.…”

The Walls Are Closing In: Postural Responses to a Virtual Reality Claustrophobic Simulation

“…More recently, visual manipulations in experimental and clinical settings use virtual reality (VR) to alter immersive virtual environments (VE) for rehabilitation [24]. VR has also been used to expose individuals to VE that can induce postural threats, such as simulated vertical heights [8,9,[25][26][27] and rotating the visual field on the pitch, yaw, and roll principle axes [26,28], that alter center of pressure (COP) dynamics and bodily kinematics and thereby, the overall postural stability. Moreover, VR is identified as a great alternative to expose individuals to different environments they otherwise avoid due to fear [8,29].…”