On the nature and evaluation of fidelity in virtual environments

In this chapter, we discuss some issues relating to the evaluation of simulations. We concentrate on simulations that involve motion of the user, but our analysis may apply to simulation in general. We argue that in the strict sense of duplication, simulation is essentially impossible: With rare exceptions, sensory stimulation in a simulator cannot be identical to sensory stimulation that is available in the system being simulated. We suggest that these differences in stimulation provide information to the user about the nature of the simulation, as such. If this information is picked up, then it may be rare for users to perceive a simulation to be “the real thing.” Researchers and developers commonly define the fidelity of simulations in terms of their tendency to give rise to illusory subjective experience in users. However, if simulation is perceived as such (that is, if perception is accurate rather than illusory), then there may be little practical value in metrics that rely on an illusory perception of reality. Metrics that assume that perception in simulations is illusory may be counterproductive if they focus the attention of researchers and developers on aspects of the simulation that are not directly relevant to issues of fidelity. We suggest that in many application domains, more useful metrics of fidelity can be developed from measurements of performance, rather than subjective experience.