Can I pass?

Perception of an accurate sense of the scale depicted in computer graphics is important for many applications. How to best characterize the accuracy of space perception in computer graphics is a question that does not have a simple answer. This paper describes the use of perceived affordances as a way of measuring the perceptual fidelity of virtual environments with respect to how well they convey information about geometric scale. The methodology involves a verbal indication that a particular action can or cannot be performed in a viewed environment. By varying the spatial structure of the environment, these affordance judgments can be used to probe how accurately viewers are able to perceive action-relevant spatial information. The result is a measure relevant to action, less subject to bias than verbal reports of more primitive properties such as size or distance, and applicable to non-virtual-environment display systems in which the actual action cannot be performed. We demonstrate the approach in an experiment comparing one type of affordance judgment, perceived passability, with judgments of size and distance in matched real world and virtual world environments.