Effect of Interpupillary Distance Mismatch on Distance and Orientation Perception in Action Space Across HMDs

Historically, distances are underestimated in virtual environments, and a mismatch between a participant's inter-pupillary distance (IPD) and the inter-axial distance (IAD) of the head-mounted display (HMD) could contribute to underestimation, but prior work has not examined how this interacts with lens type or target location in the visual field. Prior work testing the effects of IPD mismatch on distance perception in immersive virtual environments (IVEs) shows mixed results for distances within 2-10 meters. One limitation is that this work did not consider the variety of optical lenses employed in different HMDs. The lens type could affect distance perception differently depending on IPD and could affect it even more for targets appearing on the sides of the display rather than in front of the user. We examined whether the HMD type and location of targets in the virtual visual field affect perception when IPD is mismatched and matched. Using a blind walking task, participants judged the distance to targets that were either in front or to the side of the participant. One group viewed targets in the Varjo XR-3 and the other viewed them in the HTC Vive Pro. We found that distances were judged to be farther in the periphery than in front of users for both devices. Only in the HTC Vive Pro did an increase in IPD mismatch result in increased distance estimates for targets presented directly in front of the participant. Directional angular error (error observed in orienting to the target) increased as the target angle increased for both devices. However, in the Varjo XR-3, a higher IPD mismatch resulted in greater angular error when viewing targets to the side. Overall, the findings show that a mismatched IPD can affect depth and orientation judgments depending on target position in the display. However, there are differences in both FOV and resolution that could influence distance and orientation perception. A second experiment was conducted to examine whether these factors contributed to perception. To test for this, we down-sampled the Varjo XR-3 to match the horizontal field of view and resolution of the HTC Vive Pro. We found that orientation error was mostly affected by resolution and FOV as the adjusted Varjo XR-3 yielded similar orientation perception as the HTC Vive Pro. With this knowledge, researchers should consider HMDs, IPD, and viewing area in the display as possible influences on distance and orientation perception in order to make VR accessible and accurate to all users.