B.J. Correia Grácio

Motion Scaling for High-Performance Driving Simulators

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.

Tuning of the lateral specific force gain based on human motion perception in the Desdemona simulator

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.

The time constant of the somatogravic illusion

Without visual feedback, humans perceive tilt when experiencing a sustained linear 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 measured experimentally for three motion profiles with different frequency content. 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 these motion profiles. Two self-motion perception models were fitted to the experimental data and were used to obtain the time constant of the somatogravic illusion. Results showed that the time constant of the somatogravic illusion was on the order of two seconds, in contrast to the higher time constant found in fixed-radius centrifugation studies. Furthermore, the time constant was significantly affected by the frequency content of the motion profiles. Motion profiles with higher frequency content revealed shorter time constants which cannot be explained by self-motion perception models that assume a fixed time constant. Therefore, these models need to be improved with a mechanism that deals with this variable time constant. Apart from the fundamental importance, these results also have practical consequences for the simulation of sustained accelerations in motion simulators.

Optimal and Coherence Zone Comparison Within and Between Flight Simulators

In flight simulation, motion-cueing algorithms are used to transform aircraft motion into motion within the simulator limits. When looking for the best match between visual and inertial amplitude in a simulator, researchers have found that there is a range of inertial amplitudes, rather than a single inertial value, that is perceived by subjects as optimal. This zone, hereafter referred to as the optimal zone, seems to correlate to the perceptual coherence zones measured in flight simulators. However, no studies were found in which these two zones were compared. This study investigates the relation between the optimal and the coherence-zone measurements within and between different simulators. An experiment was conducted at NASA Langley Research Center, where two simulators were used to measure the optimal and the coherence zone in the sway axis. Results show that the optimal zone lies within the coherence zone. The center of the optimal zone is significantly lower than the center of the coherence zone. I...

Driver behavior comparison between static and dynamic simulation for advanced driving maneuvers

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.

Perceptual scaling of visual and inertial cues. Effects of field of view, image size, depth cues, and degree of freedom.

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.

Visual-inertial coherence zone in the perception of heading

Knowledge of human motion perception can be applied in the optimization of motion cueing algorithms. In the past it has been shown that some discrepancies between the amplitude or phase of a visual and inertial cue go unnoticed. These acceptable discrepancies are referred to as coherence zones. In the present experiment we investigate whether a coherence zone applies to the direction of visual and inertial motion cues. More specifically, we investigated how much heading of an inertial stimulus may deviate from a visual stimulus suggesting ‘straight ahead’ motion, before the ‘straight ahead’ percept falls apart. Subjects were presented with congruent visual-inertial linear horizontal motion stimuli with varying heading and incongruent visual-inertial linear horizontal motion stimuli, in which a visual cue suggesting straight ahead motion was coupled with an inertial heading cue with varying heading. Subjects judged I) whether or not they moved straight ahead, and II) whether or not the visual and inertial stimulus were congruent. We fitted psychometric curves to the combined judgments and calculated detection thresholds for a violation of either criterion. The results show that the 50% detection thresholds are larger in the incongruent than in the congruent condition. We interpret the threshold for the incongruent condition as the size of the coherence zone. In conclusion: we provide evidence of a coherence zone for heading, as wella as a measure of the size of the heading coherence zone.

Measuring dynamics of the subjective vertical and tilt using a joystick.

Humans are able to estimate the vertical direction of an Earth fixed reference frame, which estimate is known as the subjective vertical (SV). To identify the SV, a distinction must be made between accelerations due to self-motion and gravity. Previous studies on this topic measured the SV using a variety of methods possibly affecting the outcome differently. In this study subjects were sinusoidally moved around their naso-occipital axis and their SV was dynamically measured using a joystick. In half the experimental conditions, the joystick was moved with the motion and was kept vertical on other experimental conditions, thus moving against self-motion. Although physically indicating the same angle, the average perceived angle was larger when moving the joystick with the motion than against. The difference can be explained by assuming an idiotropic vector being at issue when measuring the subjective vertical, and not when measuring subjective tilt.

Perceived radial translation during centrifugation

BACKGROUND Linear acceleration generally gives rise to translation perception. Centripetal acceleration during centrifugation, however, has never been reported giving rise to a radial, inward translation perception. OBJECTIVE To study whether centrifugation can induce a radial translation perception in the absence of visual cues. METHODS To that end, we exposed 12 subjects to a centripetal acceleration with eyes closed. To avoid confounding with angular motion perception, subjects were fist rotated on-axis, and were shifted out fast and slow only after rotation sensation had vanished. They were asked for translation direction and velocity right after the shift-out, as well as after about 60 seconds of constant centrifugation. RESULTS Independent of fast or slow shift-out, the vast statistically significant majority of trials yielded an inward radial translation perception, which velocity was constant after 60 seconds of constant centrifugation. CONCLUSIONS We therefore conclude that during centrifugation, an inward radial translation perception does exist in humans, which perception reaches a constant, non-zero value during constant rotation, lasting for at least one minute. These results can be understood by high-pass filtering of otolith afferents to make a distinction between inertial and gravitational acceleration, followed by a mere integration over time to reach a constant velocity perception.

Perceived mismatch between visual and inertial cues in a simulation environment

In the field of motion 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 and scene content, 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 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. However, in this paper only the surge results are reported. Results showed that the subjective visual amplitude was affected by the field-of-view. When the field-of-view had characteristics closer to the real condition, the scaling between the visual and inertial cues was closer to one. This study demonstrated that visual characteristics affect the scaling between visual and inertial motion and that such scaling may be a good measurement for image quality in motion simulation.