Franck Mars

Driving around bends with manipulated eye-steering coordination

This study investigated the link between drivers gaze positioning and steering behavior when negotiating bends. This was conducted by directing the drivers point of gaze toward a target situated in the vicinity of the tangent point (TP), a region known to attract a significant amount of ocular fixations and thought to provide some useful input for anticipatory steering (M. F. Land & D. N. Lee, 1994). The orientation of gaze relative to the TP was manipulated and the resulting steering behavior was compared to that obtained with a free-gaze strategy. The data revealed that constraining eye movements did not impair steering behavior. On the contrary, the continuous tracking of the fixation point promoted smoother steering control, irrespective of the position of that point. This confirms that previewing the road curvature by tracking a distant point contributes to the stability of steering. The direction of the TP does not appear to be an essential parameter in that process (D. D. Salvucci & R. Gray, 2004). The results also indicate that continuously looking at the TP or further inside the bend yielded a deviation of the trajectory. This is consistent with the hypothesis that drivers look inside the lane boundaries to determine the future path (R. M. Wilkie & J. P. Wann, 2006).

A sensorimotor driver model for steering control

The work described in this paper is part of a larger research program named Partage whose goal is to appropriately share lateral control between the driver and an electronic copilot or assistance. The present study is looking for a cybernetic model of a driver steering road vehicle, which makes the sensorimotor dynamics explicit. The proposed model takes into account both visual and kinesthetic perception, and includes compensatory and anticipatory processes. As such, it extends previous works. Starting from simulated car trajectories, the unknown parameters of the model are identified using the grey box identification concept. The driver-vehicle system is then analyzed with respect to the parameter sensitivity.

Analysis of human-machine cooperation when driving with different degrees of haptic shared control

This study investigated human-machine cooperation when driving with different degrees of a shared control system. By means of a direct intervention on the steering wheel, shared control systems partially correct the vehicles trajectory and, at the same time, provide continuous haptic guidance to the driver. A crucial point is to determine the optimal level of steering assistance for effective cooperation between the two agents. Five system settings were compared with a condition in which no assistance was present. In addition, road visibility was manipulated by means of additional fog or self-controlled visual occlusions. Several performance indicators and subjective assessments were analyzed. The results show that the best repartition of control in terms of cooperation between human and machine can be identified through an analysis of the steering wheel reversal rate, the steering effort and the mean lateral position of the vehicle. The best cooperation was achieved with systems of relatively low-level haptic authority, although more intervention may be preferable in poor visibility conditions. Increasing haptic authority did not yield higher benefits in terms of steering behavior, visual demand or subjective feeling.

Supramodal effects of galvanic vestibular stimulation on the subjective vertical.

This study investigated whether the tilt of the subjective vertical induced by galvanic vestibular stimulation, demonstrated by asking subjects to set a rod to the vertical, was specific to the visual modality or could be found in two tasks relying on proprioceptive and somatosensory cues. In all cases, settings were significantly deviated in the direction of the anode, but errors were smaller in the somatosensory tasks than in the visual task. We propose that the effects observed in the somatosensory modality reflects only a modification of the central representation of gravity, whereas visual effects are also in part the consequence of unregistered ocular torsion.

Dissociation between subjective vertical and subjective body orientation elicited by galvanic vestibular stimulation.

Previous studies demonstrated that sensory stimulation could differentially affect the subjective vertical (SV) and the subjective body orientation (SBO). This suggests that the central nervous system elaborates various references of verticality in function of the task demands and of the available sensory information. In this study, we tested whether the dissociation between SV and SBO appears for a selective stimulation of the vestibular system, by using galvanic vestibular stimulation (GVS). Seated subjects performed vertical settings by controlling the orientation of a visual rod during GVS. Subjects were also instructed to evaluate the orientation of the head and trunk relative to gravity. The results revealed a large variability in the way SV and SBO were affected. In all cases, the effect of GVS on SV was not a mirror image of a distorted SBO. We propose that this dissociation is mainly determined by central processes involved in the estimation of sensory cues reliability. GVS also yielded a tilt of the head when the head was unrestrained. The results suggest that changes in actual head orientation yielded by GVS may be related to the perceived direction of gravity but cannot be explained by a compensation of an illusory orientation of the head.

Human-like cybernetic driver model for lane keeping

Abstract This paper describes a newly developed driver model which focuses on the control of steering (lane keeping) by the human driver. Obstacle avoidance and lane change are not being addressed. Our goal is to obtain a model which is i) consistent with what is known about sensorimotor and cognitive control in humans, ii) accurate (predictive) enough to support the development of efficient steering assistance system and iii) simple to be used in the context of real-time control embedded systems. Driving simulator experiments with human drivers have been carried out to validate the proposed model and to identify its parameters. The results highlight the relations between the model parameters and some characteristics of the human driver. Moreover, the model is valid over a large speed range.

The effect of visual degradation on anticipatory and compensatory steering control

It has long been held that steering a vehicle is subserved by two distinct visual processes, a compensatory one for maintaining lane position and an anticipatory one for previewing the curvature of the upcoming road. In this study, we investigated the robustness of these two steering control processes by systematically degrading their visual inputs. Performance was measured at the level of vehicle position and at the level of the actions on the steering wheel. The results show that the compensatory process is more robust to visual degradation than the anticipatory process. The results are also consistent with the idea that steering is under the supervision of a combination of compensatory and anticipatory mechanisms, although they suggest that the quality of the sensory information will determine how information is combined.

Perception of the vertical with a head-mounted visual frame during head tilt

This study addressed the question of potential disorienting effects associated to head-mounted displays, by investigating the influence of a head-fixed visual frame on the perception of the vertical when the head is tilted in the frontal plane. Subject performance in indicating the vertical was contrasted with the effect of an earth-fixed visual frame as well as with the effect of tilting the head without a frame. With the tilted frames, subjects set the rod in an intermediate direction between the gravitational vertical and the orientation of the frame. Errors were strikingly larger with a head-fixed visual frame during head tilt than with a tilted earth-based frame. The increased effect cannot be attributed to the addition of a postural effect, due to the head being tilted. Moreover, continuous vision of the frame when its orientation changed improved performance only when the head and the frame were dissociated, i.e., with an earth-based frame. Those results suggest that integrating visual information in the head-centric reference frame is crucial for spatial orientation. This property of the perceptual system should be taken into account in the design of head-mounted displays for aeronautics.

Driver adaptation to haptic shared control of the steering wheel

Although the benefits of haptic shared control of the steering wheel have been repeatedly demonstrated, longitudinal studies of how drivers adapt to this kind of system are still lacking. The present study addressed this question by comparing two groups of participants in a driving simulator for an extended time period; one group drove with a shared control system and the other drove without. After the practice, all participants drove a final trial with shared control during which a failure of the system occurred. The results show that the evolution of driving performance and the way in which drivers monitored their performance was similar for the two groups. This suggests that the drivers quickly updated their internal model of the steering system dynamics at the sensorimotor level, without further behavioural adaptation afterwards. However, it appears that the internal model was consolidated with repeated use of the system, which translated as a difficulty to compensate for the systems failure. In addition, it appears that drivers did not attempt to maintain a level of task difficulty when steering was facilitated.

Remote collaboration in virtual reality: asymmetrical effects of task distribution on spatial processing and mental workload

In the context of a remote collaboration task in virtual reality, this study aimed to analyze the effects of task distribution on the processing of spatial information and mental workload in spatial dialogs. Pairs of distant participants with specific roles (a guide and a manipulator) had to collaboratively move a virtual object in a plane factory mock-up. The displays allowed the participants to be immersed together in the virtual environment. We analyzed the dialogs that took place according to the frames of reference and the mental transformations required to produce the spatial statements. We also measured the associated mental workload. Results showed that when participants took a perspective, the manipulator’s point of view was preferred. Perspective-taking only yielded a moderate increase in mental rotations, which may explain a specifically high mental demand score for the guides’ NASA-TLX. Overall, this is in accordance with the least collaborative effort principle. This study reinforces the idea that, in collaboration, operators do not need the same aids as each other. Thus, it is not necessary to develop symmetrical tools, i.e., the same tools for all co-workers; instead, the needs of each operator should be taken into account, according to the task he has to perform. In our case, the guides would be helped with perspective-taking aids, while the manipulators would be helped with action-oriented tools.