Dwarf or giant: The influence of interpupillary distance and eye height on size perception in virtual environments

This paper addresses the question: to what extent can deliberate manipulations of interpupillary distance (IPD) and eye height be used in a virtual reality (VR) experience to influence a user's sense of their own scale with respect to their surrounding environment - evoking, for example, the illusion of being miniaturized, or of being a giant? In particular, we report the results of an experiment in which we separately study the effect of each of these body scale manipulations on users' perception of object size in a highly detailed, photorealistically rendered immersive virtual environment, using both absolute numeric measures and body-relative actions. Following a real world training session, in which participants learn to accurately report the metric sizes of individual white cubes (3"-20") presented one at a time on a table in front of them, we conduct two blocks of VR trials using nine different combinations of IPD and eye height. In the first block of trials, participants report the perceived metric size of a virtual white cube that sits on a virtual table, at the same distance used in the real-world training, within in a realistic virtual living room filled with many objects capable of providing familiar size cues. In the second block of trials, participants use their hands to indicate the perceived size of the cube. We found that size judgments were moderately correlated (r = 0.4) between the two response methods, and that neither altered eye height (± 50cm) nor reduced (10mm) IPD had a significant effect on size judgments, but that a wider (150mm) IPD caused a significant (µ = 38%, p < 0.01) decrease in perceived cube size. These findings add new insights to our understanding of how eye height and IPD manipulations can affect peoples' perception of scale in highly realistic immersive VR scenarios.