Am I Floating or Not? : Sensitivity to Eye Height Manipulations in HMD-based Immersive Virtual Environments

Eye height manipulations have previously been found to affect judgments of object size and egocentric distance in both real and immersive virtual environments. In this short paper we report the results of an experiment that explores people’s sensitivity to various offsets of their eye height in VR using a forced-choice task in a wide variety of different architectural models. Our goal is to better understand the range of eye height manipulations that can be surreptitiously employed under different environmental conditions. We exposed each of 10 standing participants to a total of 121 randomly-ordered trials, spanning 11 different eye height offsets between –80cm to +80cm, in 11 different highly detailed virtual indoor environments, and asked them to report whether they felt that their (invisible) feet were floating above or sunken below the virtual floor. We fit psychometric functions to the pooled data and to the data from each virtual environment and each participant individually. In the pooled data, we found a point-of-subjective-equality (PSE) very close to zero (–3.8cm), and 25% and 75% detection thresholds of –16.1cm and +8.6cm respectively, for an uncertainty interval of 24.7cm. We also observed some interesting variations in the results between individual rooms, which we discuss in more detail in the paper. Our findings can help to inform VR developers about users’ sensitivity to incorrect eye height placement, to elucidate the potential impact of various features of interior spaces on people’s tolerance of eye height manipulations, and to inform future work seeking to employ eye height manipulations to mitigate distance underestimation in VR.