The Influence of the Horizon Height on Spatial Perception and Experience in VR

INTRODUCTION. Despite impressive gains in computational and graphical power over the last decade, virtual reality (VR) simulations still often fail to convey a natural impression of scale, dimensions, or distances. This however is a key requirement for many potential VR applications, as for example architectural walk-throughs. Recent models of spatial vision suggest that the core of the problem lies in the way different depth cues are integrated by the human visual system similar to a mandatory weighted maximum likelihood estimation (e.g., [1]). Since most VR setups simulate only a few depth cues, strong adversary but in itself consistent depth information like a xed physical screen distance may therefore substantially compress the perceived depth dimension. However, cue integration might also bear the key to an applicable workaround solution: Varying easily adjustable simulation parameters might offer a potential for compensating for the shortcomings of more intractable depth cues. OBJECTIVE. The empirical study presented here investigates effects of changing the horizon height in VR by a frustum shift. Observations on distance estimates in reality, the form of the human visual eld, and the so-called cognitive framing effect of a restricted simulated eld of view ([2]) suggested that a raised horizon could particularly affect the perception of egocentric distances. METHOD. In a psychophysical experiment eight participants estimated three main dimensions and two egocentric distances in 20 virtual rectangular rooms from two different scene sets. In addition, possible side effects of the experimental parameter were roughly evaluated by a semantic differential rating in eight principal experiential categories in subsets of four rooms. The stimuli were presented on a calibrated desktop VR system. Radiosity-rendered interiors were generated using a custom-made tool that allowed to hide the manipulation of the experimental parameter by a balanced variation of scene features. RESULTS. Albeit verbal distance estimates are known for showing high variances between subjects, relative horizon height and perceived egocentric distances were signicantly correlated (correlation coefcient r=0.16**, p=0.003): The underestimation of distances was reduced by 29 on average. Whereas the inuence of the experimental parameter on exocentric dimensions (horizontal r=0.01, vertical r=0.07) and rated experience were below signicance level and obviously irrelevant. DISCUSSION. The results are in accordance with both the cognitive framing theory and the model of mandatory fusion of depth cues. Our ndings suggest that a raised horizon height is particularly suitable for improving the perceived ego-location in VR without negatively affecting other perceptual properties. Besides this practical improvement of VR simulations, the study shows that VR can also be effectively used in basic vision research