Body movement strategies to initiate the crossing of a street in front of traditional and self-driving cars in young and older adults

International audienceBACKGROUND AND AIM: The safety of elderlies is a key societal issue, especially when considering that 48% of pedestrian fatalities involve people aged 65 or more (Sécurité Routière 2017-France). Aging affects street crossing behavior, with a decrease of walking speed or more risky decisions because elderly people have difficulties to estimate the approaching speed of vehicles, especially in complex situations. In young adults, recent work focused on body movement performed to initiate the crossing, showing a top down sequence of advancement along the antero-posterior axis: the head initiates the crossing movement, followed by the shoulders, elbows, wrists, hips, knees and ankles. Identifying such motion invariants can be particularly useful in the context of self-driving vehicles which aim at predicting the intent of crossing. In this study, we aim at investigating body movement strategies performed before crossing in older adults in complex mixed traffic. METHODS: 30 young adults (YA, 21-39yo) and 30 older adults (OA, 68-81yo) were asked to cross (or not) a virtual two-way street by walking in a simulator. Participants performed a total of 120 trials where we manipulated: the type of vehicles (Conventional and/or Self driving car, the latest always stopping to let the pedestrian cross the street), their speed (30 or 50km/h), their position on the lane (far/near lane), as well as the temporal gap available to cross the street (1,2,3,4 or 5s). After computing temporal body segment motion and orientations, we analyzed the delays in initiating the crossing movement for the head, shoulders and hips with respect to the feet. We also performed hierarchical clustering to identify specific groups of behavior. RESULTS: Preliminary results show a top-down sequence of forward body motion, starting from the head to the feet, whatever the traffic condition and the group. In OA, the head initiates the motion sooner than YA wrt their feet. Moreover, while the horizontal angle profile of the head, shoulders and hips does not allow to identify invariants due to the large variety of behaviors before crossing, the trunk tilt angle profile appears to be a relevant marker for predicting the intent to cross the street. CONCLUSIONS: While aging was shown to affect street crossing decisions, our results highlight consistent behavior between YA and OA regarding trunk tilt profile when initiating the crossing. In line with previous work on YA, we also show a top down sequence of advancement of body segments. Future work is needed to use our results to predict the intent of crossing on a new database. Beside the choice to cross the street, future work is also needed to understand body segment motion and walking speed profile while crossing

Effects of motorcycle simulator configurations on steering control and gaze behavior in bends.

International audienceThe recent development of motorcycle simulators has made it possible to study rider behavior in safe conditions. However, their use still raises validity issues. Our study examined how riders’ steering and gaze behaviors and subjective experience are influenced by motorcycle roll tilt and reverse steering, which are considered to be essential factors in real-life motorcycle riding. The results revealed that tilting the motorcycle in the roll plane did not lead to significant changes in rider behavior, gaze sampling, or perceived realism. The steering control strategy adopted by riders did, however, significantly influence these results. A direct steering control strategy meant that riders took a racing path and scanned the road far in advance. When reverse steering was implemented, however, riders chose to take a “safety path”, as recommended by training manuals. Reverse steering also received the highest realism score. However, steering control was more difficult, as shown by the larger number of lane departures recorded and achange in the trade-off between guiding and look-ahead fixations. This suggests that although reverse steering matches riders’ real control behavior and improves the subjective experience of simulator riding, it is hindered by an inadequate internal model of vehicle dynamics

The Effects of Age and Traffic Density on Street-Crossing Behavior

Past research has shown that road users accept shorter time gaps when the waiting time/number of vehicles they let pass before attempting to merge into the traffic increases. While elderly pedestrians are known to be an extremely vulnerable group of road users, very few studies dealt with the effect of environmental constraints and crossing complexity on this population’s safety. The present study aimed at determining whether or not street-crossing decisions and behavior of younger and older pedestrians were differently affected by a traffic flow. In an interactive street-crossing task, we assessed whether mean time gap and crossing decisions depended on the position of the gap pedestrians selected into the traffic stream. Results revealed that irrespective of their age pedestrians accepted a smaller time gap when they chose the second interval of the traffic compared to the first one. Contrasting with previous hypotheses, this traffic-related behavior was not accompanied by an increase in the decisions risk. The findings also showed that the transition threshold from rejecting to accepting time gaps was shorter when the second interval was selected compared to the first one. This increment in task constraints might help younger and older pedestrians alike to perceive action possibilities more accurately and to be better attuned to traffic conditions by comparing gaps between each other. This opens an interesting perspective in the understanding and the training of the ability of elderly road users to remain accurate in their judgements

Simulation de conduite moto : effets du roulis visuel sur les stratégies visuelles et le contrôle de trajectoire lors de la prise de virage

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Effect of driving environment complexity and dual task on eye blink rate

Holmqvist, K., Mulvey, F., & Johannson, R. (2013). Abstracts of the 17th European Conference on Eye Movements 2013. Journal of Eye Movement Research, 6(3). https://doi.org/10.16910/jemr.6.3.1Eye measures have been shown to be relevant indicators of mental workload. Empirical results revealed a relationship between mental workload and eye blinks, depending on the task constraints. In a single-task, the blink rate seems to drop as a function of greater task complexity, while the opposite result has been found in a dual-task. The goal of this study was to examine the effect of driving-task complexity on blink rate, using a single versus a dual task. For the experiment, 20 participants drove in 3 driving environment complexities: low (dual-carriageway), medium (rural-road) and high (urban-road). Each condition was presented alone, or associated with a vocal reaction-time-task to an auditory stimulus. Results showed a strong effect of driving-task complexity, as blink rate decreased from low to high environment complexity. By contrast and differing from previous research, the dual-task condition didn’t affect blink rate. This suggests that the reaction time and the driving task were performed simultaneously, and that the reaction -time -task didn’t affect the driving -task. The effects of a dual task on blink rate might probably occur in case of attentional switching. It could be valuable to examine in a future experiment the effect of environment complexities on blink rate in a new dual-task paradigm: driving and mental-arithmetic

Vieillissement, pratique sportive et coordinations visuomotrices

L'étude des effets de l'âge souligne principalement la logique de dégradation à laquelle est associée le vieillissement. Cependant, il apparaît également en parallèle qu'un facteur d'expérience se développe positivement avec l'âge. L'évolution des performances au cours du vieillissement représenterait alors l'expression conjointe de deux 'sphères' d'influences agissant selon une dynamique opposée. La question principale posée dans cette étude est de savoir si la sollicitation régulière et répétée des processus de coordination visuomotrice dans le cadre d'une pratique sportive vient contrebalancer les effets de l'âge et permet aux individus âgés pratiquants de maintenir un niveau de performance similaire à celui de sujets jeunes. Il s'agit dans la continuité de préciser l'origine des effets liés au vieillissement et la nature exacte des modifications associées à la pratique sportive, en s'intéressant aux hypothèses de compensation et de préservation. Six groupes de participants ont été constitués en fonction de l'âge (20-30, 60-70 et 70-80 ans) et de la pratique sportive (joueurs de tennis et non joueurs) et testés dans des tâches sélectionnées pour rendre compte de la précision des réponses selon le niveau de contraintes imposé. Les principaux résultats montrent des effets différents du vieillissement et de la pratique sportive selon le niveau de contraintes considéré. Il apparaît que, lorsque l'acteur a la possibilité de guider sa réponse en continu, aucune différence liée à l'âge n'est observée. Les participants âgés semblent donc composer efficacement avec un déclin des processus élémentaires identifiés par ailleurs. A l'opposé, lorsque la situation implique un contrôle de l'action et de son déclenchement sur la base de processus cognitifs, les effets négatifs de l'âge sont contrebalancés par la pratique. Les résultats obtenus suggère que la nature des modification associées à la pratique sportive relèverait davantage d'une explication du type compensation.Studies interested in the effects of age show mainly that performance decreases with advancing age. However, compared with this negative approach of aging, experience also develops positively with age. Changes in performance during aging should then be considered as the combined influence of two different dimensions that act in an opposite way. The main question of this study is to know if the regular and repeated activation through tennis practice of processes involved in visuomotor coordinations could counterbalance the negative effects of age in order that old tennis players maintain a similar level of performance as younger subjects. As a second objective, it was necessary to precise the origin of the age-related effects and the exact nature of observed modifications associated with sport practice. In this last perspective, two different hypotheses, i.e. preservation and compensation, were considered. Six different groups of subjects participated in this study according to age (20-30, 60-70 and 70-80 years old) and sport practice (Tennis players and non players) and were tested in various tasks carried out to question responses accuracy as a function of tasks' contraints. Results showed differents effect of age and sport practice according to tasks' contraints. In an interception experiment, it appeared that, when actor could guide his movement continuously until the arrival of the moving object on the target, no age difference was observed. Old participants seem then to deal efficiently with elementary processes' declines appearing elsewhere. On the contrary, when tasks involve initiation of actions on the basis of cognitive processes, the negative effects of age were counterbalanced with practice. Results obtained in this study suggest that changes associated with sport practice are in line with a compensation hypothesis.ORSAY-PARIS 11-BU Sciences (914712101) / SudocORSAY-PARIS11-Bib. STAPS (914712103) / SudocSudocFranceF

Gaze and steering strategies while driving around bends with shoulders

International audienceThe installation of shoulders on rural roads to create more forgiving roads encourages drivers to cut corners on right-hand bends, but the underlying mechanisms are poorly understood. Since eye movements and steering control are closely coupled, this study investigated how the presence of a shoulder influences drivers' gaze strategies. To this end, eighteen drivers negotiated right-hand bends with and without a shoulder on a simulated rural road. In the presence of a shoulder, participants modified their visual sampling of the road by directing their gaze further inside the bend. At the same time, their lane position was deviated inward throughout the bend and the vehicle spent more time out of the lane. These results suggest that the shoulder influences the visual processes involved in trajectory planning. Recommendations are made to encourage drivers to keep their eyes and vehicle in the driving lane when a shoulder is present

Aging and tennis playing in a coincidence-timing task with an accelerating object: the role of visuomotor delay.

International audienceThe purpose of the present study was to determine whether playing a specific ball sport, such as tennis, could maintain the coincidence-timing (CT) performance of older adults at a similar level to that of younger ones. To address this question, tennis players and nonplayers of three different age ranges (ages 20-30, 60-70, and 70-80 years) performed a simple CT task consisting of timing their response (pressing a button) to coincide with the arrival of a stimulus at a target. The stimulus moved at either an accelerating, constant, or decelerating velocity. As expected, all participants were affected by the velocity manipulation, which led to late and early responses to accelerating and decelerating stimuli, respectively. Whereas this response bias was increasingly pronounced with advancing age in nonplayers, no difference was found among player groups of different ages. Finally, we showed that the length of the visuomotor delay could explain the effect of nonconstant velocities

Driving around bends with or without shoulders: The influence of bend direction

International audiencePaved shoulders have long been used to create "forgiving" roads where drivers can maintain control of their vehicles even when as they drift out of the lane. While the safety benefits of shoulders have been well documented, their effects on driver behavior around curves have scarcely been examined. The purpose of this paper is to fill this gap by assessing whether the addition of shoulders affects driver behavior differently as a function of bend direction. Driver behavior in a driving simulator was analyzed on left and right curves of two-lane rural roads in the presence and absence of 0.75-m and 1.25-m shoulders. The results demonstrated significant changes in drivers' lateral control when shoulders were provided. In the absence of oncoming traffic, the shoulders caused participants to deviate more toward the inner lane edge at curve entry, at the apex and at the innermost position on right bends but not left ones. In the presence of oncoming traffic, this also occurred at the apex and the innermost position, leading participants to spend more time off the lane on right curves. Participants did not slow down in either traffic condition to compensate for steering farther inside, thereby increasing the risk of lane departure on right curves equipped with shoulders. These findings highlight the direction-specific influence of shoulders on a driver's steering control when driving around bends. They provide arguments supporting the idea that drivers view paved shoulders as a new field of safe travel on right curves. Recommendations are made to encourage drivers to keep their vehicle within the lane on right bends and to prevent potential interference with cyclists when a shoulder is present

Effects of visual roll on steering control and gaze behavior in a motorcycle simulator

International audienceThe goal of this study was to examine the effects of visual roll tilt on gaze and riding behavior when negotiating a bend using a motorcycle simulator. To this end, experienced motorcyclists rode along a track with a series of right and left turns whilst the degree of visual roll tilt was manipulated in three different conditions. Gaze behavior was analyzed by using the tangent point as a dynamic spatial reference; the deviation of gaze to this particular point was computed in both the horizontal and vertical directions. Steering control was assessed in terms of the lateral positioning, steering stability and number of lane departures. In the no-roll condition, the motorcyclists tracked a steering point on the road ahead, which was compatible with the hypothesis of ‘‘steer where you look” behavior. In the roll condition, our results revealed that the horizontal distribution of gaze points relative to the tangent point was preserved. However, significantly more fixations were made further ahead of the tangent point in the vertical direction. This modification of visual behavior was coupled with a degradation in steering stability and an offset in lateral positioning, which sometimes led to lane departures. These results are discussed with regard to models of visual control of steering for bend negotiation