Nagaoka University of Technology, Nagaoka, Niigata, Japan
When do people experience the surrounding world as real? Unless they experience exceptional conditions such as depersonalization, most people rarely question the reality of their everyday environment. Immersive virtual reality (VR) using head-mounted displays, however, can readily evoke such doubt. In other words, the feeling that an expected sense of reality is somehow missing marks the starting point for exploring the nature of reality. Many VR researches have assumed that multisensory synchrony and congruency are necessary conditions for producing a sense of reality. As a result, experiences arising from discrepant multisensory stimuli have received relatively little attention. To address this issue, we developed a VR system that manipulates somatosensory perception by applying external pulling forces to the user's body and conducted two experiments. The first was a laboratory-based motorcycle riding experiment involving 41 licensed adult drivers (a within-subject design). The second focused on snowboard riding and consisted of laboratory training followed by a real-world follow-up study involving 18 adults with no prior snowboarding experience (a between-subject design). In both experiments, there were three conditions: an external force corresponding to the expected inertial force (IF), an external force applied in the opposite direction (OF), or no external force (NF). Thus, the two force conditions (IF and OF) represented contrasting assumptions about the physical world: the IF condition approximated real-world physics, whereas the OF violated it. The psychological evaluations from both experiments consistently showed that the mere presence of an external force (IF and OF conditions), regardless of its direction, reduced VR sickness and enhanced the subjective sense of reality. Furthermore, participants in the second experiment exhibited significantly different body movements during training under the IF condition compared with the other conditions. More intriguingly, in the follow-up study of the second experiment, participants who trained in the IF and OF conditions, despite having no prior snowboarding experience, learned to snowboard more quickly on a real ski slope compared to participants in the NF condition. In other words, participants who experienced external force during VR training, regardless of the direction of the applied force, subsequently performed adaptive body movements in the real world. These findings are inconsistent with the predictions of sensory conflict theory, which attributes the loss of reality primarily to inconsistencies among sensory modalities. Instead, they suggest that congruency between multisensory stimuli is not a necessary condition for generating a sense of reality or for facilitating the acquisition of adaptive bodily behavior. In a future where VR becomes deeply integrated into everyday life, the objects with which we interact in virtual environments may be considered metaphysically real. More fundamentally, however, the source of reality may lie not in eliminating discrepancies among sensory stimuli, but in the participant's capacity to receive them. Reality is a qualitative experience that cannot be meaningfully compared on a quantitative scale. In this sense, imagination may itself be real.