Rest-Frame Cueing for Cybersickness Mitigation in Virtual Reality Helicopter Flight Simulation
Authors: Englebert Boris , Tillema Guido , Foorthuis Lodewijck 
Published: June 2024

The integration of Virtual Reality (VR) into flight simulation not only presents an opportunity to revolutionize flight crew training from an economical point of view, compared to conventional flight simulation methods. However, it also introduces challenges, such as an increased occurrence of cybersickness, potentially undermining the effectiveness of VR-based training. To optimize the benefits of VR, addressing the heightened likelihood of cybersickness is crucial. The most widely accepted theory for cybersickness attributes its emergence to a sensory conflict between visual inputs from the virtual environment and the motion sensed by the vestibular system The mitigation of this sensory conflict is considered an effective strategy for combating cybersickness. A potential method to dissolve this sensory conflict is to introduce a visual reference to the actual environment in the virtual environment, for which the resulting visual inputs correspond to the motion that is sensed in the actual environment. The presentation of such a visual reference in virtual environments, also referred to rest-frame cueing, is as such hypothesized to be an mitigation method for cybersickness, although the effectiveness of rest-frames on cybersickness mitigation is dependent on the precise manner in which the rest frame is cued to the operator. An example of how rest-frame cueing for cybersickness mitigation is through mixed reality (MR), in which the virtual environment is visually blended with the actual environment, which has shown promising results for the mitigation of cybersickness.However, it has also been found that while MR reduces cybersickness, it also leads to a decline in pilot performance in virtual environment flight training, attributed to reduced immersion and lower simulation fidelity. As an alternative, it is hypothesized that a visual grid in the virtual environment that is fixed to the orientation of the actual environment, also referred to as a Virtual Reference Grid (VRG), can be an effective alternative rest-frame cueing strategy that offers similar cybersickness reduction benefits as MR but may be more conducive to maintaining simulation fidelity. This study explores the effectiveness of a VRG as a form of rest-frame cueing on cybersickness mitigation, aiming to minimize cybersickness without compromising pilot performance. The effectiveness of a VRG in helicopter flight simulation for cybersickness mitigation and pilot performance was investigated by means of a human-in-the- loop experiment, featuring experienced helicopter pilots from the Royal Dutch Air Force. The experimental setup includes an AgustaWestland AW139 helicopter flight model, low-fidelity flight controls, and the Varjo XR-3 visual device for rendering the virtual environment. A bespoke scenario, featuring the challenging ADS-33E-PRF pirouette Mission Task Element (MTE), serves as the backdrop for evaluating cybersickness and pilot performance metrics. Participants navigate three conditions: No Visual Reference, VRG Reference, and MR Reference. Post-trial, participants report their cybersickness levels using the Misery Scale (MISC), with measures in place to prevent excessive build-up between conditions.The results highlighted subtle differences in pilot performance, with the VRG rest-frame negatively affecting distance and heading control in the execution of the ADS-33 pirouette Mission Task Element (MTE). However, it was also observed that the performance degradation for distance control in the VRG Reference condition was less severe than in the MR Reference condition, suggesting that VRG rest-frame cueing may be less detrimental for certain aspects of pilot performance.The contrasting outcomes between MR and VRG rest-frame cueing emphasize the need for a deeper exploration of the role of cognitive processing of rest-frame cues for effective cybersickness mitigation. The study suggests that participants’ lack of cognitive awareness regarding the fixed nature of the VRG with respect to the actual environment contributed to its limited impact on mitigating cybersickness. This insight underscores the critical importance of effective design in rest frame cues for cybersickness mitigation in VR. In light of these findings, it is evident that designing rest-frame cues aligned with participants’ cognitive processes and enhancing their awareness of the virtual environment is crucial for the purpose of cybersickness mitigation and promoting pilot performance in VR helicopter flight simulation.