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International audience; The aim of this study was to characterize the behavior of older peo- ple when intercepting a moving gap, with reference to that pro- duced by younger people. Participants were asked to intercept a moving inter-vehicular space within a train of vehicles, by modulat- ing their speed if necessary. Five initial distances to the interception location were manipulated (Offset), without the knowledge of the participants, requiring distinct speed regulations. The analyses focused on displacements kinematics as well as on the associated visual information taking strategies. The results indicate several simi- larities in the behaviors produced by two populations. Functional speed regulations are initiated early and persist until the intercep- tion. These regulations allow for safe interception. The visual strat- egies deployed by the older participants are also relatively close to those of the younger participants, with the main areas of interest located on the vehicles located upstream of the interval. The results also reveal differences between the two populations. The regulations produced by older drivers are initiated late in negative Offset giving rise to some extent to unsafe behavior. These results are discussed in relation to the decrease in motion detection thresholds with age. Our dataset could be particularly useful in view of the design of driver assistance systems for older drivers.

Background Impaired gait adaptability is one of the major causes of falls among older adults by producing inappropriate gait adjustments in cluttered environments. Training programs designed to improve gait adaptability behavior in a systemic approach may prevent falls in older adults. Recently, the technology of virtual reality has appeared as a relevant gait training tool based on its training implementation potential. The present study was designed to compare the effectiveness of a virtual reality gait training program (VR group) for improving gait adaptability behavior and thus, reducing the risk of falls relative to a conventional training program of Nordic walkway (NW group). We hypothesize that the virtual reality gait training program will lead to greater gait adaptability improvements.Methods The protocol describes a randomized controlled trial with pre-tests, post-tests, retention tests and follow-up. Forty healthy independent living community dweller participants (65–80 years) will be allocated, after a general medical examination, to the VR or the NW group for a training program of six weeks. Primary outcome related to gait adaptability capacities and acceptance of the virtual reality device will be assessed in pre- and post-intervention and one month after the completion of the training program (retention). A follow-up will be done during the 12 months after the completion of the gait training program.Discussion This study will demonstrate the relative relevance of a gait training program in virtual reality versus a conventional one for improving gait adaptability behavior in healthy older adults and thus preventing falls.Trial registration CERSTAPS (IRB00012476-2022-14-10-200, 14 October 2022)

International audience; Subjective vertical in presence of visual or auditory cues: Towards an allocentric dependence? The psychological differentiation approach initiated by Witkin and Asch (1948) on the perception of verticality yielded the concept of field dependence, through which observers could be distinguished from their tendency to be influenced or not by a visual frame tilt when judging the direction of gravity (i.e., subjective vertical [SV]). Since, field dependence has been mostly considered as a marker for a preferential sensibility to visual information with respect to other sensory modalities (e.g., vestibular or somatosensory). This pilot study aims at tackling the issue of field dependence in spatial perception from a novel perspective. We hypothesized that orientation cues issued from a same reference frame centered on near surroundings (i.e. allocentric reference frame) could lead to comparable distinctions between observers, whatever the sensory modality involved in conveying these cues. We tested 23 participants on a SV adjustment task facing two allocentric-visual or auditory-scenes. Our results show a strong correlation between SV settings in both sensory conditions where the allocentric scene was tilted. These findings suggest that individuals could differ regarding the process of spatial information issued from a same reference frame, irrespective from the sensory modality conveying the information.; Reçu le 14 décembre 2017, Accepté le 9 septembre 2019 L'étude de la perception de la verticale initiée par Witkin et Asch (1948) a abouti au concept de dépendance à l'égard du champ, distinguant les individus dans leur propension à être influencés par l'inclinaison d'un cadre visuel sur le jugement de la direction gravitaire (i.e., verticale subjective [VS]). Depuis, cette dépendance est souvent considérée comme révélatrice d'une sensibilité préférentielle aux informations visuelles par rapport à d'autres modalités sensorielles (e.g., vestibulaires ou somesthésiques). Ce travail pilote vise à reconsidérer la notion de dépendance à l'égard du champ dans la perception spatiale. Nous faisons l'hypothèse que des informations d'orientation issues d'un même cadre de référence centré sur l'environnement (i.e., référentiel allocentré) puissent conduire à une distinction comparable entre participants, quelle que soit la modalité sensorielle considérée. Face à deux scènes allocentrées (visuelle et sonore), 23 participants ont été testés sur une tâche d'ajustement de la VS. Nos résultats montrent une forte corrélation entre les ajustements dans les deux conditions sensorielles où la scène allocentrée était inclinée. Ceci suggère que les individus peuvent se différencier dans le traitement des informations spatiales issues d'un même cadre de référence, et ce de la même façon quelle que soit la modalité sensorielle permettant de relayer ces informations. Mots clés : perception spatiale, dépendance à l'égard du champ, cadre de référence, orientation, vision, audition

Findings from virtual reality applications in general and driving or flight simulators in particular, are frequently generalized to the study of human behavior. Thus, it is crucial to ensure that the virtuality of the experimental setup has little or no effect on perception of space and motion. Most studies show that observers immersed in virtual environments (VE) perceive virtual space as compressed relative to the real world, resulting in systematic underestimations of egocentric distance. Parallax and stereopsis, known to be important depth cues for distance perception, at least for short distances, are rarely used together in driving simulators, so their interactive role during driving tasks is still not clear. Inter-individual differences in misperception are also referred to, though few studies have explored this. The aim of this study was, first, to determine whether egocentric distance perception in driving simulation depends on two depth cues, binocular disparity and motion parallax, and, second, to examine the effect of inter-individual differences. Several conditions were tested, both with and without stereoscopic vision of the scene and/or motion parallax of the head. We focused first on a range of long distances, 40–80 m (Experiment 1) and subsequently widened the range to distances from 5 to 80 m, thereby including short distances where stereopsis should be more relevant (Experiment 2). The study reveals great inter-individual variability, clearly distinguishing two participant profiles. However, results suggest that such differences do not depend on the availability of motion parallax and stereoscopic vision. The findings also show that an initial familiarization phase, under conditions similar to those of the experiments, can be predictive of participants’ perceptual behavior.

Optic flow has been found to be a significant cue for static observers’ perception of distance travelled. In previous research conducted in a large-scale immersive display (CAVE), adding viewpoint oscillations to a radial optic flow simulating forward self-motion was found to modulate this perception. In the present two experiments, we investigated (1) whether the improved distance travelled perceptions observed with an oscillating viewpoint in a CAVE were also obtained when the subjects were wearing a head mounted display (HMD, an Oculus Rift) and (2) whether the absence of viewpoint oscillations during treadmill walking was liable to affect the subjects’ perception of self-motion. In Experiment 1, static observers performed a distance travelled estimation task while facing either a purely linear visual simulation of self-motion (in depth) or the same flow in addition to viewpoint oscillations based on the subjects’ own head oscillations previously recorded during treadmill walking. Results show that the benefits of viewpoint oscillations observed in a CAVE persisted when the participants were wearing an HMD. In Experiment 2, participants had to carry out the same task while walking on a treadmill under two different visual conditions simulating self-motion in depth: the one with and the other without the visual consequences of their head translations. Results showed that viewpoint oscillations did not improve the accuracy of subjects’ distance travelled estimations. A comparison between the two experiments showed that adding internal dynamic information about actual self-motion to visual information did not allow participants better estimates.

International audience; Although discrete auditory stimuli have been found useful for emergency braking, the roleof continuous speed-related auditory feedback has not been investigated yet. This pointmay though be of importance in electric vehicles in which acoustic cues are drasticallychanged. The present study addressed this question through two experiments. In experi-ment 1, 12 usual drivers were exposed to naturalistic auditory feedback mimicking thoseissued from electric cars, while facing dynamic visual scenes in a 3D driving simulator.After being passively travelled up to a sustained constant speed, subjects had to stop theircar in front of a traffic light that unexpectedly turned to red. Modifications of the speed-related auditory feedback did not impact braking initiation and regulation. In experiment2, synthesized auditory feedback based on the Shepard-Risset glissando was provided to anew sample of 15 usual drivers in the same task. Pitch variations of this acoustic stimulus,although not scaled to an absolute speed, were manipulated as a function of visual speedchanges. Changing the mapping between pitch variations of the synthesized auditory feed-back and visual speed changes induced adjustments on braking which depended on accel-eration/deceleration feedback. These findings stressed the importance of the acousticcontent and its dynamics for car speed control.

International audience; When static observers are presented with a visual simulation of forward self-motion, they generally misestimate distance travelled relative to a previously seen distant target: It has been suggested that this finding can be accounted for by a ‘‘leaky path integration’’ model. In the present study, using a similar experimental procedure, this result was confirmed. It was also established that combining the translational optical flow with simulated head oscillations (similar to those during natural walking) improved the subjects’ perception of the distance travelled in comparison with a purely translational flow. This improvement may be attributable to the fact that an optic flow pattern resembling that associated with walking enhances the path integration process. In a subsequent experiment, we investigated whether it was the biological or the rhythmical characteristics of the simulation that enhanced the subjects’ estimates of the distance travelled. The results obtained confirm that adding rhythmic components to the optic flow pattern improved the accuracy of subjects’ perception of the distance travelled. However, no significant differences between biological and rhythmical oscillations were detected. These results relate to recent studies on the effects of smooth and jittering optic flows on vection onset and strength. One possible conclusion is that oscillations may increase the global retinal motion and thus improve the vection and path integration processes. Another possibility is that the nonmonotonous pattern of retinal motion induced by oscillatory inputs may maintain optimum sensitivity to the optic flow over time and thus improve the accuracy of subjects’ perception of the distance travelled.

International audience; Although many studies have looked at the perceptual-cognitive strategies used to make anticipatory judgments in sport, few have examined the informational invariants that our visual system may be attuned to. Using immersive interactive virtual reality to simulate the aerodynamics of the trajectory of a ball with and without sidespin, the present study examined the ability of expert and novice soccer players to make judgments about the ball's future arrival position. An analysis of their judgment responses showed how participants were strongly influenced by the ball's trajectory. The changes in trajectory caused by sidespin led to erroneous predictions about the ball's future arrival position. An analysis of potential informational variables that could explain these results points to the use of a first-order compound variable combining optical expansion and optical displacement.

International audience; In everyday life, humans and most animals need to navigate in their environment, which produces multiple sources of perceptual information, such as locomotor cues (i.e. proprioceptive, efference copy and vestibular cues) and optic flow. However, few studies focused on the role of the visual consequences of walking (bob, sway, and lunge head motion) on self-motion perception. In a previous study, in which static observers were confronted to a visual simulation of forward motion, we have shown that adding rhythmical components to an optic flow pattern improved the accuracy of subjects' travelled distance estimations, in comparison with a purely translational flow. These results were attributable to the fact that oscillations may increase the global retinal motion and thus improve vection. Another hypothesis was that, walking step frequency being a significant cue in speed perception, visual consequences of step frequency might be at the origin of better estimations.To test this, we used the same experimental procedure in which observers, immersed inside a 4-sided CAVE, had to indicate when they thought they had reached a previously seen target. We tested whether different oscillation frequencies would affect the perception of distance travelled. Observers were confronted with 4 conditions of optic flows simulating forward self-motion. The first condition was generated by purely translational optic flow, at constant speed. The three other conditions of flows were vertical triangular oscillations with three kinds of frequencies added to linear forward motion, at the same forward speed. Results show that two groups can be distinguished. Regarding the first group, as in the previous study, adding rhythmic components improves the perception of distance travelled. For the second group, the higher the frequency, the earlier the answers, suggesting that these subjects related the oscillation frequency to their step frequency and perceived themselves as moving faster.Meeting abstract presented at VSS 2017