Quantifying Spatial Presence

The human visual system uses a series of complex assumptions, defaults, and biases to reconstruct the depth relationships in the three-dimensional world from the two-dimensional image on the retina. Some of these biases are independent of the image on the retina itself, and dependent on whether the observer is viewing a picture of the real world or the real world itself. For investigators interested in the sense of presence, this characteristic of the visual system presents the possibility to quantitatively measure the spatial presence evoked by a virtual environment by determining the degree to which these biases are evident. Two case studies are presented, one in which a virtual environment resembled the real world, and one in which it resembled pictures. The evaluation metrics discussed are particularly important because the benchmark they provide is not necessarily how well the virtual environment replicates the real world, but whether it seems real to the human perceptual system.