Optic Flow in Driving Simulators

This paper describes how, in the case of driving simulators, optic flow is generated as a user’s vehicle traverses a three-dimensional virtual environment. The amount of optic flow is greatest directly in front and to the sides of the vehicle, with optic flow being zero at the point of expansion. In the first experiment, the method of paired-comparisons was used to investigate perceived optic flow for four sizes of geometric field of view (GFOV) (25, 45, 65, and 85 horizontal degrees). Results established that subjects could accurately differentiate the amount of optic flow for the four levels of GFOV. In addition, subjects perceived the velocity of on-coming vehicles to be faster when the GFOV was large. The authors designed a second experiment to investigate the production of specific values of vehicle velocity. In the second experiment, subjects were asked to accelerate their vehicle from a stop until they perceived it was going either 30 or 60 mph. The sizes of GFOV were set at 25, 55, or 85 horizontal degrees. Subjects overestimated velocity for the 30 mph condition. When asked to produce a velocity of 30 mph they produce a velocity of 50 mph. Their production of 60 mph was much more accurate. An interaction of the velocity asked for and GFOV, showed that accuracy increased as the GFOV increased. These experiments suggest that the perception of optic flow in driving simulators is not the same as in the real-world. This results in a conflict between what is perceived from observation of optic flow in a simulated virtual environment and what is reported by the vehicle’s speedometer.