Tilt-coordination is a commonly used method for simulating a sustained linear acceleration in a dynamic driving simulator. It consists of using the tilt of the simulator in order to orient gravity relative to the driver’s head in a similar way as the gravito-inertial acceleration (GIA) is oriented in the real vehicle [1]. According to Groen et al. [1], the key issue of tilt-coordination is to apply sufficient simulator tilt without the angular velocity exceeding the perceptual threshold. Starting from their experiment of using only tilt to simulate acceleration, we developed a new experiment in which we use both linear acceleration and tilt. The final acceleration is simulated using different ratios of linear acceleration and tilt. We inquired if changing the ratio acceleration/tilt will influence the perception of the final acceleration and if this perception is biased by external conditions, like the presence or absence of optical flow. For this, we used a dynamic driving simulator, equipped with an X-Y motion platform and a 6 DOF (degrees of freedom) hexapod [2]. The subjects were submitted to a predefined scenario of linear displacement on a straight road. The scenario consisted of displacement of the car at constant velocity toward a wall and braking at a certain distance before the wall. Simultaneously with the beginning of the braking, the wall disappeared instantly and the subjects were asked to tell if the car stopped before or after the wall. The braking was simulated using 5 different ratios of acceleration/tilt, but the sum of the final deceleration was always the same (-0.8 m/s2). The experiment was divided in two parts, using two different visual scenarios (with and without optic flow during braking). Preliminary results suggest that the braking is perceived stronger as more tilt is used for the simulation and weaker as more linear acceleration is used. In this case, the final perception would depend on the quantity of acceleration and tilt, even if, according to Holly and McCollum [3], they are perceptually equivalent.
[1] E. L. Groen and W. Bles. How to use body tilt for the simulation of linear self motion. Journal of Vestibular Research, 14(5):375–385, 2004. [2] T. Chapron and J.P. Colinot. The new PSA Peugeot-Citroën Advanced Driving Simulator: Overall design and motion cue algorithm, Proceedings for Driving Simulation Conference North America, Iowa, USA, 2007. [3] J.E. Holly and G. McCollum. The shape of self-motion perception – I. Equivalence classification for sustained motion. Neuroscience. 70(2):461-486,1996.