Physiological responses to simulated and on-road driving.

Driving simulators have become an increasingly popular tool to study and assess drivers. Physiological measurements not only provide an important index of an individual's presence in the virtual environment, but they also permit us to compare simulated and on-road experiences. However, at this point, few studies examining the ecological validity of simulated driving have included physiological variables. In a first study, we embedded three surprising events into a typical simulated road circuit. The first event consisted of a car pulling out suddenly from the shoulder of the road, while the remaining two events consisted of a green traffic light changing to amber as the driver approached the intersection. We noted statistically significant elevations in the mean heart rate (MHR) response to virtual events of about 4beats per minute (bpm) during the 15s immediately following the events. In a second study, we directly compared heart rate, oxygen consumption (VO(2)), and mean ventilation (MV(E)) responses to similar simulated and on-road drives. The change in physiological variables from baseline to driving was similar between simulated and on-road conditions, and a very strong correlation between simulated and on-road driving values for MV(E) (r=0.90) was observed. MHR and maximum heart rate (HR(max)) were nonetheless significantly higher during on-road drives. These studies suggest that the level of immersion of a fixed base simulator is great enough to elicit presence, and achieve both relative and absolute validity for certain physiological parameters. Nonetheless, the absolute responses between virtual and real world experiences remain different. For both research and evaluation purposes, it is critical that we better understand the impact of the driver's perceived level of risk or difficulty during simulation on their driving behaviour and physiological responses.