Differences of gait adaptability behavior between young and healthy older adults during a locomotor pointing task in virtual reality.

BACKGROUND: Gait adaptability training programs to prevent falls in healthy older adults can be proposed in virtual reality. The development of training programs requires the characterization of the target population. RESEARCH QUESTION: Before proposing an innovative training program to develop gait adaptability behavior of healthy older adults in fully immersive virtual reality, we had to compare gait adaptability behavior between healthy older adults and young adults in virtual reality. METHODS: Twenty healthy older adults (with no fall history) and twenty young adults performed a goal-directed locomotion task in a totally secure virtual reality set-up. Gait adaptability behavior was investigated via a set of measures taking into account gait speed, pointing accuracy, and the evolution of the relationship between the participant and the environment through both inter-trial and trial-by-trial analyses. Mann-Whitney tests and linear regressions were performed to determine potential age differences. RESULTS: The results reveal some common and specific strategies in gait adaptability behavior between healthy older and young adults. In both populations, successive gait adjustments depend on the state of the agent-environment system. However, older adults walked more slowly than young adults (p < .001) with a greater coupling at the end of the target approach (p = .003). SIGNIFICANCE: In the context of fall prevention in healthy older adults, fully immersive VR appears as a relevant tool to propose relevant gait training programs to improve gait adjustments.

An interdisciplinary framework to optimize the anticipation skills of high-level athletes using virtual reality.

The ambition of our contribution is to show how an interdisciplinary framework can pave the way for the deployment of innovative virtual reality training sessions to improve anticipation skills in top-level athletes. This improvement is so challenging that some authors say it is like "training for the impossible". This framework, currently being implemented as part of a project to prepare athletes for the 2024 Olympic Games in Paris, based on the ecological-dynamics approach to expertise, is innovative in its interdisciplinary nature, but also and above all because it overcomes the limitations of more traditional training methods in the field designed to optimize anticipation skills in top-level athletes. The ambition is to tackle successive challenges ranging from the design of virtual partners and opponents to the deployment of training programs in virtual reality, while ensuring the acceptability and acceptance of such innovative virtual reality training protocols and measuring associated workloads.

Evaluation of assistance systems allowing older drivers to intercept moving inter-vehicular space.

Introduction: The objective of the present study was to test two Advanced Driving Assistance Systems (ADAS) designed to help older drivers to intercept a moving inter-vehicular space. Method: Older and younger drivers were asked to intercept a moving inter-vehicular space within a train of vehicles in a driving simulator. Three ADAS conditions (No-ADAS, Head Down, Head Up) as well as five distinct speed regulation conditions were tested. Vehicle trajectory, gaze behavior and acceptance were analyzed. Results: Our results reveal that the ADAS tested make it possible to perform the interception task but also to reduce the variability of the behavior produced. They also indicate that the location of the augmented information provided by the ADAS directly impacts the information-gathering strategy implemented. Finally, whereas younger divers reported mixed levels of ADAS acceptance, older drivers reported a good level of acceptance. Discussion: All these results could be particularly useful with a view of designing ADAS for older drivers.

Honeybees Use Multiple Invariants to Control Their Altitude.

How do bees perceive altitude changes so as to produce safe displacements within their environment? It has been proved that humans use invariants, but this concept remains little-known within the entomology community. The use of a single invariant, the optical speed rate of change, has been extensively demonstrated in bees in a ground-following task. Recently, it has been demonstrated that another invariant, the splay angle rate of change, could also be used by bees to adjust their altitude. This study aims to understand how bees use these invariants when they are available simultaneously. This issue has been addressed using an experimental setup providing discordant information to bees. We have shown that when the two invariants were available, bees performed ground-following tasks relying primarily on optical speed rate of change. Conversely, when optical speed rate of change was less easily accessible, splay angle rate of change was prioritized, unless the bees perceive danger. Taken together, these results illustrate how the joint use of several invariants allows bees to produce adaptive behaviors.

An experimental setup for decoupling optical invariants in honeybees' altitude control.

Bees outperform pilots in navigational tasks, despite having 100,000 times fewer neurons. It is commonly accepted in the literature that optic flow is a key parameter used by flying insects to control their altitude. The ambition of the present work was to design an innovative experimental setup that would make it possible to determine whether bees could rely simultaneously on several optical invariants, as pilots do. We designed a flight tunnel to enable manipulation of an optical invariant, the Splay Angle Rate of Change (SARC) and the restriction of the Optical Speed Rate of Change (OSRC) in the optic flow. It allows us to determine if bees use the SARC to control their altitude and to identify the integration process combining these two optical invariants. Access to the OSRC can be restricted by using different textures. The SARC can be biased thanks to motorized rods. This device allows to record bees' trajectories in different visual configurations, including impoverished conditions and conditions containing contradictory information. The comparative analysis of the recorded trajectories provides first time evidence of SARC use in a ground-following task by a non-human animal. This new tunnel allows a precise experimental control of the visual environment in ecological experimental conditions. Therefore, it could pave the way for a new type of ecologically based studies examining the simultaneous use of several information sources for navigation by flying insects.

Validation of an immersive virtual reality device accepted by seniors that preserves the adaptive behavior produced in the real world.

Falls in the elderly are a major societal issue. Virtual reality appears as a relevant tool to propose gait training programs to prevent the occurrence of falls. The use of a head-mounted display allows overground walking during fully immersive virtual training sessions. Our long-term ambition is to develop gait training programs with a head-mounted display to propose enjoyable and personalized training content for the elderly. Before proposing these programs, several methodological precautions must be taken. The first concerns the supposed similarity of the adaptive behavior produced in the real world and in virtual reality. The second concerns the acceptance of the virtual reality device before and after use. Twenty older adults performed a locomotor pointing task in three conditions including a real-world condition, a virtual-world condition consisting in a replica of the real-world condition, and a virtual condition in which the locomotor pointing task was performed in a different context. From feet positions in relation to the position of a target, gait adaptability behavior was investigated. In line with previous studies, step adjustments (needed and produced) were investigated through a combination of inter-trial and trial-by-trial analyses. The results highlighted that participants adopted the same gait adaptability behavior whatever the type of environment (real vs. virtual). Gait analyses suggested the use of a generic control mechanism based on information-movement coupling. We also demonstrated that older adults accepted the virtual reality device before and after use. With these methodological locks removed, it is now possible to design training programs in virtual reality to prevent falls in the elderly.

Floor and ceiling mirror configurations to study altitude control in honeybees.

To investigate altitude control in honeybees, an optical configuration was designed to manipulate or cancel the optic flow. It has been widely accepted that honeybees rely on the optic flow generated by the ground to control their altitude. Here, we create an optical configuration enabling a better understanding of the mechanism of altitude control in honeybees. This optical configuration aims to mimic some of the conditions that honeybees experience over a natural water body. An optical manipulation, based on a pair of opposed horizontal mirrors, was designed to remove any visual information coming from the floor and ceiling. Such an optical manipulation allowed us to get closer to the seminal experiment of Heran & Lindauer 1963. Zeitschrift für vergleichende Physiologie47, 39-55. (doi:10.1007/BF00342890). Our results confirmed that a reduction or an absence of ventral optic flow in honeybees leads to a loss in altitude, and eventually a collision with the floor.

Studying the timescale of perceptual-motor (re)calibration following a change in visual display gain.

Experiencing a non-1:1 mapping between perception and action in everyday life is not common. It could be considered as a problem for our perceptual-motor system because of the need to adapt our goal-directed movement to different gains between movement and task spaces. In the Human Computer Interface domain, the main example of such a situation consists in switching from one operating system to another which requires to adapt our movement to different Control Display gains. The aim of the study was to characterize the perceptual-motor calibration process following a sudden change in control display gain. Sixteen participants manipulated a mouse computer to move a cursor on the screen. The discrete aiming task consisted on reaching the target from a starting target position as fast and as accurately as possible. Our methodology consisted in suddenly manipulating the gain between both spaces following a three-step adaptation methodology (baseline condition followed by a perturbation and return to baseline condition). Results demonstrated that not only participants produce adaptive behavior following several types of perturbations, but they were also able to do it at a very short timescale. As the calibration process described in the present study may play a significant role in the acquisition of accurate perceptual-motor skills involving the use of devices that augment human fine motor capabilities (e.g., telesurgery, mouse and joystick), we conclude that this study could have important implications in the domain of Human-Computer Interaction (HCI) as well as in the domain Human Equipment Interaction.

Ecological Entomology: How Is Gibson's Framework Useful?

To date, numerous studies have demonstrated the fundamental role played by optic flow in the control of goal-directed displacement tasks in insects. Optic flow was first introduced by Gibson as part of their ecological approach to perception and action. While this theoretical approach (as a whole) has been demonstrated to be particularly suitable for the study of goal-directed displacements in humans, its usefulness in carrying out entomological field studies remains to be established. In this review we would like to demonstrate that the ecological approach to perception and action could be relevant for the entomologist community in their future investigations. This approach could provide a conceptual and methodological framework for the community in order to: (i) take a critical look at the research carried out to date, (ii) develop rigorous and innovative experimental protocols, and (iii) define scientific issues that push the boundaries of the current scientific field. After a concise literature review about the perceptual control of displacement in insects, we will present the framework proposed by Gibson and suggest its added value for carrying out research in the field of behavioral ecology in insects.

Acceptance of a Virtual Reality Headset Designed for Fall Prevention in Older Adults: Questionnaire Study.

BACKGROUND: Falls are a common phenomenon among people aged 65 and older and affect older adults' health, quality of life, and autonomy. Technology-based intervention programs are designed to prevent the occurrence of falls and their effectiveness often surpasses that of more conventional programs. However, to be effective, these programs must first be accepted by seniors. OBJECTIVE: Based on the technology acceptance model, this study aimed to examine the acceptance among older adults before a first use of a virtual reality headset (VRH) used in an intervention program designed to prevent falls. METHODS: A sample of 271 French older adults (mean age 73.69 years, SD 6.37 years) voluntarily and anonymously filled out a questionnaire containing the focal constructs (perceived usefulness, perceived enjoyment, perceived ease of use, intention to use, fall-related self-efficacy, and self-avoidance goals) adapted to the VRH, which was designed to prevent falls. RESULTS: The results of the structural equation modeling analysis showed that intention to use the VRH was positively predicted by perceived usefulness, perceived enjoyment, and perceived ease of use. Perceived usefulness of the VRH was also negatively predicted by fall-related self-efficacy (ie, the perceived level of confidence of an individual when performing daily activities without falling) and positively predicted by self-avoidance goals (ie, participating in a physical activity to avoid physical regression). CONCLUSIONS: A better understanding of the initial acceptance among older adults of this VRH is the first step to involving older adults in intervention programs designed to prevent falls using this kind of device.

Eye position affects flight altitude in visual approach to landing independent of level of expertise of pilot.

The present study addresses the effect of the eye position in the cockpit on the flight altitude during the final approach to landing. Three groups of participants with different levels of expertise (novices, trainees, and certified pilots) were given a laptop with a flight simulator and they were asked to maintain a 3.71° glide slope while landing. Each participant performed 40 approaches to the runway. During 8 of the approaches, the point of view that the flight simulator used to compute the visual scene was slowly raised or lowered with 4 cm with respect to the cockpit, hence moving the projection of the visible part of the cockpit down or up in the visible scene in a hardly noticeable manner. The increases and decreases in the simulated eye height led to increases and decreases in the altitude of the approach trajectories, for all three groups of participants. On the basis of these results, it is argued that the eye position of pilots during visual approaches is a factor that contributes to the risk of black hole accidents.

A scale-based approach to interdisciplinary research and expertise in sports.

After more than 20 years since the introduction of ecological and dynamical approaches in sports research, their promising opportunity for interdisciplinary research has not been fulfilled yet. The complexity of the research process and the theoretical and empirical difficulties associated with an integrated ecological-dynamical approach have been the major factors hindering the generalisation of interdisciplinary projects in sports sciences. To facilitate this generalisation, we integrate the major concepts from the ecological and dynamical approaches to study behaviour as a multi-scale process. Our integration gravitates around the distinction between functional (ecological) and execution (organic) scales, and their reciprocal intra- and inter-scale constraints. We propose an (epistemological) scale-based definition of constraints that accounts for the concept of synergies as emergent coordinative structures. To illustrate how we can operationalise the notion of multi-scale synergies we use an interdisciplinary model of locomotor pointing. To conclude, we show the value of this approach for interdisciplinary research in sport sciences, as we discuss two examples of task-specific dimensionality reduction techniques in the context of an ongoing project that aims to unveil the determinants of expertise in basketball free throw shooting. These techniques provide relevant empirical evidence to help bootstrap the challenging modelling efforts required in sport sciences.

Judging arrival times of incoming traffic vehicles is not a prerequisite for safely crossing an intersection: Differential effects of vehicle size and type in passive judgment and active driving tasks.

Using a fixed-base driving simulator we compared the effects of the size and type of traffic vehicles (i.e., normal-sized or double-sized cars or motorcycles) approaching an intersection in two different tasks. In the perceptual judgment task, passively moving participants estimated when a traffic vehicle would reach the intersection for actual arrival times (ATs) of 1, 2, or 3s. In line with earlier findings, ATs were generally underestimated, the more so the longer the actual AT. Results revealed that vehicle size affected judgments in particular for the larger actual ATs (2 and 3s), with double-sized vehicles then being judged as arriving earlier than normal-sized vehicles. Vehicle type, on the other hand, affected judgments at the smaller actual ATs (1 and 2s), with cars then being judged as arriving earlier than motorcycles. In the behavioral task participants actively drove the simulator to cross the intersection by passing through a gap in a train of traffic. Analyses of the speed variations observed during the active intersection-crossing task revealed that the size and type of vehicles in the traffic train did not affect driving behavior in the same way as in the AT judgment task. First, effects were considerably smaller, affecting driving behavior only marginally. Second, effects were opposite to expectations based on AT judgments: driver approach speeds were smaller (rather than larger) when confronted with double-sized vehicles as compared to their normal-sized counterparts and when confronted with cars as compared to motorcycles. Finally, the temporality of the effects was different on the two tasks: vehicle size affected driver approach speed in the final stages of approach rather than early on, while vehicle type affected driver approach speed early on rather than later. Overall, we conclude that the active control of approach to the intersection is not based on successive judgments of traffic vehicle arrival times. These results thereby question the general belief that arrival time estimates are crucial for safe interaction with traffic.

The Influence of the 'Trier Social Stress Test' on Free Throw Performance in Basketball: An Interdisciplinary Study.

The aim of the present study was to explore the relationship between stress and sport performance in a controlled setting. The experimental protocol used to induce stress in a basketball free throw was the Trier Social Stress Test (TSST) and its control condition (Placebo-TSST). Participants (n = 19), novice basketball players but trained sportspersons, were exposed to two counterbalanced conditions in a crossover design. They were equipped with sensors to measure movement execution, while salivary cortisol and psychological state were also measured. The task consisted of two sequences of 40 free throws, one before either the TSST or Placebo-TSST and one after. Physiological and psychological measures evidenced that the TSST induced significant stress responses, whereas the Placebo-TSST did not. Shooting performance remained stable after the TSST but decreased after the Placebo-TSST. We found no effect of the TSST or Placebo-TSST on movement execution. A multivariate model of free throw performance demonstrated that timing, smoothness and explosiveness of the movements are more relevant to account for beginner's behavior than stress-related physiological and psychological states. We conclude that the TSST is a suitable protocol to induce stress responses in sport context, even though the effects on beginners' free throw performance and execution are small and complex.

High- and Low-Order Overtaking-Ability Affordances: Drivers Rely on the Maximum Velocity and Acceleration of Their Cars to Perform Overtaking Maneuvers.

OBJECTIVE: The aim of this study was to answer the question, Do drivers take into account the action boundaries of their car when overtaking? BACKGROUND: The Morice et al. affordance-based approach to visually guided overtaking suggests that the "overtake-ability" affordance can be formalized as the ratio of the "minimum satisfying velocity" (MSV) of the maneuver to the maximum velocity (V(max)) of the driven car. In this definition, however, the maximum acceleration (A(max)) of the vehicle is ignored. We hypothesize that drivers may be sensitive to an affordance redefined with the ratio of the "minimum satisfying acceleration" (MSA) to the A(max) of the car. METHOD: Two groups of nine drivers drove cars differing in their A(max). They were instructed to attempt overtaking maneuvers in 25 situations resulting from the combination of five MSA and five MSV values. RESULTS: When overtaking frequency was expressed as a function of MSV and MSA, maneuvers were found to be initiated differently for the two groups. However, when expressed as a function of MSV/V(max) and MSA/A(max), overtaking frequency was quite similar for both groups. Finally, a multiple regression coefficient analysis demonstrated that overtaking decisions are fully explained by a composite variable comprising MSA/A(max) and the time required to reach MSV. CONCLUSION: Drivers reliably decide whether overtaking is safe (or not) by using low- and high-order variables taking into account their car's maximum velocity and acceleration, respectively, as predicted by "affordance-based control" theory. APPLICATION: Potential applications include the design of overtaking assistance, which should exploit the MSA/A(max) variables in order to suggest perceptually relevant overtaking solutions.

Is perception of self-motion speed a necessary condition for intercepting a moving target while walking?

While it has been shown that the Global Optic Flow Rate (GOFR) is used in the control of self-motion speed, this study examined its relevance in the control of interceptive actions while walking. We asked participants to intercept approaching targets by adjusting their walking speed in a virtual environment, and predicted that the influence of the GOFR depended on their interception strategy. Indeed, unlike the Constant Bearing Angle (CBA), the Modified Required Velocity (MRV) strategy relies on the perception of self-displacement speed. On the other hand, the CBA strategy involves specific speed adjustments depending on the curvature of the target's trajectory, whereas the MRV does not. We hypothesized that one strategy is selected among the two depending on the informational content of the environment. We thus manipulated the curvature and display of the target's trajectory, and the relationship between physical walking speed and the GOFR (through eye height manipulations). Our results showed that when the target trajectory was not displayed, walking speed profiles were affected by curvature manipulations. Otherwise, walking speed profiles were less affected by curvature manipulations and were affected by the GOFR manipulations. Taken together, these results show that the use of the GOFR for intercepting a moving target while walking depends on the informational content of the environment. Finally we discuss the complementary roles of these two perceptual-motor strategies.

Drivers' decision-making when attempting to cross an intersection results from choice between affordances.

In theory, a safe approach to an intersection implies that drivers can simultaneously manage two scenarios: they either choose to cross or to give way to an oncoming vehicle. In this article we formalize the critical time for safe crossing (CT cross ) and the critical time for safe stopping (CT stop ) to represent crossing and stopping possibilities, respectively. We describe these critical times in terms of affordances and empirically test their respective contribution to the driver's decision-making process. Using a driving simulator, three groups of participants drove cars with identical acceleration capabilities and different braking capabilities. They were asked to try to cross an intersection where there was an oncoming vehicle, if they deemed the maneuver to be safe. If not, they could decide to stop or, as a last resort, make an emergency exit. The intersections were identical among groups. Results showed that although the crossing possibilities (CT cross ) were the same for all groups, there were between-group differences in crossing frequency. This suggests that stopping possibilities (CT stop ) play a role in the driver's decision-making process, in addition to the crossing possibilities. These results can be accounted for by a behavioral model of decision making, and provide support for the hypothesis of choice between affordances.

Intercepting a moving traffic gap while avoiding collision with lead and trail vehicles: gap-related and boundary-related influences on drivers' speed regulations during approach to an intersection.

Using a fixed-base driving simulator, 15 participants actively drove their vehicle across a rural road toward an intersection. Their task was to safely cross the intersection, passing through a gap in the train of incoming traffic. Spatiotemporal task constraints were manipulated by varying the initial conditions (offsets) with respect to the time of arrival of the traffic gap at the intersection. Orthogonally manipulating the motion characteristics of the lead and trail vehicles forming the traffic gap allowed evaluating the influences of the global (gap-related) and local (lead/trail-vehicle-related) aspects of the inter-vehicular interval. The results revealed that the different initial offsets gave rise to functional, continuous and gradual adjustments in approach speed, initiated early on during approach to the intersection. Drivers systematically accelerated during the final stages of approach, on average crossing the gap slightly ahead of the center of the traffic gap. A special-purpose ANOVA demonstrated an influence of (global) gap characteristics such as gap size and speed. Further analyses demonstrated that the motion characteristics of the lead vehicle exerted a stronger influence on approach behavior than the motion characteristics of the trail vehicle. The results are interpreted as signing the online regulation of approach speed, concurrently based on intercepting the (center of the) traffic gap and avoiding collision with the lead and trail vehicles.

Intersection crossing considered as intercepting a moving traffic gap: effects of task and environmental constraints.

Safely crossing an intersection requires that drivers actively control their approach to the intersection with respect to characteristics of the flow of incoming traffic. To further our understanding of the perceptual-motor processes involved in this demanding manoeuvre, we designed a driving simulator experiment in which 13 participants actively negotiated intersections by passing through a gap in the train of incoming traffic. Task constraints were manipulated by varying the size of the traffic gap and the initial conditions with respect to the time of arrival of the traffic gap at the intersection. Environment constraints were manipulated by varying the intersection geometry through changes in the angle formed by the crossroads. The results revealed that the task constraints systematically gave rise to continuous and gradual adjustments in approach velocity, initiated well before arriving at the intersection. These functionally appropriate adjustments allowed the drivers to safely cross the intersection, generally just slightly ahead of the center of the traffic gap. Notwithstanding the fact that the geometry of the intersection did not affect the spatiotemporal constraints of the crossing task, approach behavior varied systematically over geometries, suggesting that drivers rely on the traffic gap's bearing angle. Overall, the pattern of results is indicative of a continuous coupling between perception and action, analogous to that observed in locomotor interception tasks.

The education of attention as explanation of variability of practice effects: learning the final approach phase in a flight simulator.

The present study reports two experiments in which a total of 20 participants without prior flight experience practiced the final approach phase in a fixed-base simulator. All participants received self-controlled concurrent feedback during 180 practice trials. Experiment 1 shows that participants learn more quickly under variable practice conditions than under constant practice conditions. This finding is attributed to the education of attention to the more useful informational variables: Variability of practice reduces the usefulness of initially used informational variables, which leads to a quicker change in variable use, and hence to a larger improvement in performance. In the practice phase of Experiment 2 variability was selectively applied to some experimental factors but not to others. Participants tended to converge toward the variables that were useful in the specific conditions that they encountered during practice. This indicates that an explanation for variability of practice effects in terms of the education of attention is a useful alternative to traditional explanations based on the notion of the generalized motor program and to explanations based on the notions of noise and local minima.