Advanced driving simulators aim at rendering the motion of a vehicle with maximum fidelity, which requires increased mechanical travel, size, and cost of the system. Motion cueing algorithms reduce the motion envelope by taking advantage of limitations in human motion perception, and the most commonly employed method is just to scale down the physical motion. However, little is known on the effects of motion scaling on motion perception and on actual driving performance. This paper presents the results of a European collaborative project, which explored different motion scale factors in a slalom driving task. Three state-of-the-art simulator systems were used, which were capable of generating displacements of several meters. The results of four comparable driving experiments, which were obtained with a total of 65 participants, indicate a preference for motion scale factors below 1, within a wide range of acceptable values (0.4-0.75). Very reduced or absent motion cues significantly degrade driving performance. Applications of this research are discussed for the design of motion systems and cueing algorithms for driving simulation.

Humans perceive tilt when experiencing a sustained acceleration.This tilt illusion is commonly referred to as the somatogravic illusion. Although the physiological basis of the illusion seems to be well understood, the dynamic behavior is still subject to discussion. In this study the dynamic behavior of the illusion was modeled and the time constant was measured experimentally. Subjects were exposed to pure centripetal accelerations in the lateral direction and were asked to indicate their tilt percept by means of a joystick. Variable radius centrifugation during constant angular rotation was used to generate three different motion profrles. Results showed that the time constant of the somatogravic illusion is in the order of two seconds contradicting the high time constant found in fixed radius centrifugation studies. The model fit was not improved when using an otolith model sensitive to high frequency accelerations. Apart from the fundamental importance, these results also have practical consequences for the simulation of sustained accelerations in motion simulators.

The goal of the present study was to explore how simulator motion cuing affects the driver's control performance of a car. Steering behavior was used as a measure of control performance. The experimental task was a slalom maneuver in which the velocity of the car was limited to 70 km/h. Subjective and objective variables were measured. The paper describes the objective steering behavior. The slalom task was driven under four conditions in which the lateral motion scale factors were 1 (one-to-one lateral motion), 0.7, 0.4, and 0 (no-motion), respectively. In total, 16 participants completed the experiment. The study showed that the motion condition affects the steering wheel behavior. The general tendency is that less steering correction took place when the magnitude of the motion cues was increased, which was quantified by two performance indicators. First, the number of steering wheel reversals was reduced when the motion cue magnitude was increased. Second, the amount of relatively high-frequency correction was reduced with increasing motion cue magnitude. It is concluded that motion feedback can improve the driver's control performance in an extreme scenario such as a slalom maneuver. Therefore, the effect of motion on control performance must be considered when a driving simulator study addressing control performance is designed.

Generally, motion simulators present motion and visual cues different from each other due to the physical limitations of the motion platform. Nonetheless, high fidelity motion platforms are capable of simulating some maneuvers one-to-one, i.e., motion cues equal to visual cues. However, one-to-one simulation is normally not preferred by subjects and the simulator motion is reported as too strong. In this study we investigated whether this overestimation depends on the frequency and amplitude of inertial motion. The stimuli in this study consisted of translations in the lateral direction. The Desdemona research simulator was used to generate the motion profiles. Six sinusoidal profiles with different combinations of amplitude and frequency were used as reference stimuli. For every experimental condition, the visual and inertial information had equal frequency but different amplitude. Subjects had to change the inertial motion amplitude until they obtained the best relation between the two sources of motion information. Our results showed that stimuli with high amplitude were associated with smaller motion gains than stimuli with lower amplitude. The same occurred for stimuli with higher frequency when compared to stimuli with lower frequency. The findings in this study suggest that a dynamic scaling algorithm for inertial motion could improve the perceived realism of motion simulation.

In the field of motion-based simulation, it was found that a visual amplitude equal to the inertial amplitude does not always provide the best perceived match between visual and inertial motion. This result is thought to be caused by the "quality" of the motion cues delivered by the simulator motion and visual systems. This paper studies how different visual characteristics, like field of view (FoV) and size and depth cues, influence the scaling between visual and inertial motion in a simulation environment. Subjects were exposed to simulator visuals with different fields of view and different visual scenes and were asked to vary the visual amplitude until it matched the perceived inertial amplitude. This was done for motion profiles in surge, sway, and yaw. Results showed that the subjective visual amplitude was significantly affected by the FoV, visual scene, and degree-of-freedom. When the FoV and visual scene were closer to what one expects in the real world, the scaling between the visual and inertial cues was closer to one. For yaw motion, the subjective visual amplitudes were approximately the same as the real inertial amplitudes, whereas for sway and especially surge, the subjective visual amplitudes were higher than the inertial amplitudes. This study demonstrated that visual characteristics affect the scaling between visual and inertial motion which leads to the hypothesis that this scaling may be a good metric to quantify the effect of different visual properties in motion-based simulation.

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In advanced driving maneuvers, such as a slalom maneuver, it is assumed that drivers use all the available cues to optimize their driving performance. For example, in curve driving, drivers use lateral acceleration to adjust car velocity. The same result can be found in driving simulation. However, for comparable curves, drivers drove faster in fixed-base simulators than when actually driving a car. This difference in driving behavior decreases with the use of inertial motion feedback in simulators. The literature suggests that the beneficial effect of inertial cues in driving behavior increases with the difficulty of the maneuver. Therefore, for an extreme maneuver such as a fast slalom, a change in driving behavior is expected when a fixed-base condition is compared to a condition with inertial motion. It is hypothesized that driving behavior in a simulator changes when motion cues are present in extreme maneuvers. To test the hypothesis, a comparison between No-Motion and Motion car driving simulation was done, by measuring driving behavior in a fast slalom. A within-subjects design was used, with 20 subjects driving the fast slalom in both conditions. The average speed during the Motion condition was significantly lower than the average speed during the No-Motion condition. The same was found for the peak lateral acceleration generated by the car model. A power spectral density analysis performed on the steering wheel angle signal showed different control input behavior between the two experimental conditions. In addition, the results from a paired comparison showed that subjects preferred driving with motion feedback. From the lower driving speed and different control input on the steering wheel, we concluded that motion feedback led to a significant change in driving behavior.