Visual augmentation of deck-landing-ability improves helicopter ship landing decisions.

When attempting to land on a ship deck tossed by the sea, helicopter pilots must make sure that the helicopter can develop sufficient lift to be able to safely touchdown. This reminder of affordance theory led us to model and study the affordance of deck-landing-ability, which defines whether it is possible to land safely on a ship deck depending on the helicopter's available lift and the ship's deck heave movements. Two groups of participants with no piloting experience using a laptop helicopter simulator attempted to land either a low-lifter or a heavy-lifter helicopter on a virtual ship deck by either triggering a pre-programmed lift serving as the descent law if it was deemed possible to land, or aborting the deck-landing maneuver. The deck-landing-ability was manipulated by varying the helicopter's initial altitude and the ship's heave phase between trials. We designed a visual augmentation making visible the deck-landing-ability, and thus enabling participants to maximize the safety of their deck-landing attempts and reduce the number of unsafe deck-landing. The visual augmentation presented here was perceived by participants as a means of facilitating this decision-making process. The benefits were found to have originated from the clear-cut distinction it helped them to make between safe and unsafe deck-landing windows and the display of the optimal time for initiating the landing.

A multi-scale analysis of basketball throw in virtual reality for tracking perceptual-motor expertise.

To benefit from virtual reality (VR) as a complementary tool for training, coaches must determine the proper tools and variables for tracking sports performance. We explored the basketball shooting at several scales (basket-ball, ball-player, and player systems) by monitoring success-rate, and ball and body kinematics. We measured how these scales of analysis allowed tracking players' expertise and perceptual sensitivity to basket distance. Experienced and novice players were instructed to naturally throw and swish an instrumented ball in a stereoscopically rendered virtual basket. We challenged their perceptual-motor systems by manipulating the distance of the virtual basket while keeping the surrounding environment unchanged. The success-rate accounted for the players' shooting adjustments to the manipulation of basket distance and allowed tracking their expertise. Ball kinematics also reflected the manipulation of distance and allowed detecting gender, but did not reflect the players' expertise. Finally, body kinematics variables did not echo players' adjustments to the distance manipulation but reflected their expertise and gender. The results gained at each scale of analysis are discussed with regard to the simulator's construct, biomechanical, and psychological fidelity.

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.

Ecological design of augmentation improves helicopter ship landing maneuvers: An approach in augmented virtuality.

Helicopter landing on a ship is a visually regulated "rendezvous" task during which pilots must use fine control to land a powerful rotorcraft on the deck of a moving ship tossed by the sea while minimizing the energy at impact. Although augmented reality assistance can be hypothesized to improve pilots' performance and the safety of landing maneuvers by guiding action toward optimal behavior in complex and stressful situations, the question of the optimal information to be displayed to feed the pilots' natural information-movement coupling remains to be investigated. Novice participants were instructed to land a simplified helicopter on a ship in a virtual reality simulator while minimizing energy at impact and landing duration. The wave amplitude and related ship heave were manipulated. We compared the benefits of two types of visual augmentation whose design was based on either solving cockpit-induced visual occlusion problems or strengthening the online regulation of the deceleration by keeping the current [Formula: see text] variable around an ideal value of -0.5 to conduct smooth and efficient landing. Our results showed that the second augmentation, ecologically grounded, offers benefits at several levels of analysis. It decreases the landing duration, improves the control of the helicopter displacement, and sharpens the sensitivity to changes in [Formula: see text]. This underlines the importance for designers of augmented reality systems to collaborate with psychologists to identify the relevant perceptual-motor strategy that must be encouraged before designing an augmentation that will enhance it.

Total hip arthroplasty after failed fixation of a proximal femur fracture: Analysis of 59 cases of intra- and extra-capsular fractures.

INTRODUCTION: The indications for total hip arthroplasty (THA) after failed internal fixation of a proximal femur fracture vary. Published studies on this topic are broad-ranging and do not distinguish between intracapsular and extracapsular fractures. This led us to conduct a retrospective analysis comparing the clinical outcomes, radiological outcomes, technical problems and complications between these two types of fractures. HYPOTHESIS: The functional outcomes of THA after an extracapsular fracture will be worse than the ones after an intracapsular fracture. MATERIAL AND METHODS: This was a retrospective, single-center study of 59 THA cases performed after internal fixation of a proximal femur fracture. These procedures were performed between 2002 and 2013 in 58 patients (22 men, 36 women). There were 40 intracapsular fractures and 19 extracapsular fractures. The initial fracture fixation involved a screw-plate (n=50), intramedullary nail (n=6) or screws (n=3). The mean patient age at the time of THA was 67 years [22-94]. The THA was performed an average of 2.8 years [0.2-28] after the fracture. The posterolateral approach was used in 55 cases (93%). Ten patients (17%) had the fixation hardware removed before the THA procedure, on average at 30 months [1-240] after the fracture. During the THA procedure, a cemented stem was used in 31 cases (53%) and a cementless stem in 28 cases (47%). A cementless press-fit cup was used in 56 cases (95%), of which 35 were dual mobility cups (60%), and a cemented cup was used in the other 3 cases (5%). All patients were reviewed by a physician not involved in the surgical procedures who performed a clinical and radiological examination. RESULTS: No patients were lost to follow-up; two patients died. Ten patients suffered an intraoperative femur fracture (17%) and four suffered a dislocation (2 early, 2 late) (6.8%). Nine hips had to be reoperated (15%), of which five required an implant change (8.5%). There were significantly more intraoperative fractures and postoperative complications in the THA cases after extracapsular fracture. With a mean follow-up of 38 months [12-149], the mean PMA and Harris scores were 14.6 [3-18] and 74 [10-100], respectively; these scores were significantly lower in the THA cases after extracapsular fracture (p<0.05). With an endpoint of revision with implant change, the overall 40-month survival was 94% (95% CI: 0.25-0.55); it was 97% (95% CI: 0.62-0.85) for the intracapsular fracture cases and 84% (95% CI: 0.39-0.75) for the extracapsular fracture cases (p<0.05). CONCLUSION: Secondary THA after failed fixation of proximal femur fractures has more complications than primary THA. Subgroup analysis identified more technical problems in the THA cases after extracapsular fracture and a higher number of complications, particularly dislocation and periprosthetic fractures. LEVEL OF EVIDENCE: IV - Retrospective study.

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.

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.

Visual control of walking velocity.

Even if optical correlates of self-motion velocity have already been identified, their contribution to the control of displacement velocity remains to be established. In this study, we used a virtual reality set-up coupled to a treadmill to test the role of both Global Optic Flow Rate (GOFR) and Edge Rate (ER) in the regulation of walking velocity. Participants were required to walk at a constant velocity, corresponding to their preferred walking velocity, while eye height and texture density were manipulated. This manipulation perturbed the natural relationship between the actual walking velocity and its optical specification by GOFR and ER, respectively. Results revealed that both these sources of information are indeed used by participants to control walking speed, as demonstrated by a slowing down of actual walking velocity when the optical specification of velocity by either GOFR or ER gives rise to an overestimation of actual velocity, and vice versa. Gait analyses showed that these walking velocity adjustments result from simultaneous adaptations in both step length and step duration. The role of visual information in the control of self-motion velocity is discussed in relation with other factors.

Top-level players' visual control of interceptive actions: Bootsma and van Wieringen (1990) 20 years later.

Using a two-step approach, Van Soest et al. (2010) recently questioned the pertinence of the conclusions drawn by Bootsma and Van Wieringen (1990) with respect to the visual regulation of an exemplary rapid interceptive action: the attacking forehand drive in table tennis. In the first step, they experimentally compared the movement behaviors of their participants under conditions with and without vision available during the execution of the drive. In the second step, through simulation they evaluated the extent to which a preprogrammed pattern of muscle stimulation acting on the dynamical characteristics of the musculoskeletal system could explain the patterns of movement observed, including the phenomena of kinematic convergence and compensatory variability. In this contribution, we show how methodological and conceptual shortcomings, pertaining to both parts of Van Soest et al.'s study, severely limit the impact of their findings. We argue that their conclusion-denying the possibility of visual regulation of rapid interceptive actions-cannot be upheld in the light of the existing evidence, while Bootsma and Van Wieringen's conclusion-in favor of the visual regulation of rapid interceptive actions in top-level players- still holds strong, even after 20 years. Irrespective of the trends of the moment, we suggest that both appropriate experimentation and principled theorization need to be deployed before a model-based predictive architecture can be considered as a serious alternative to a (more parsimonious) information-based control architecture.

Environmental constraints modify the way an interceptive action is controlled.

This study concerns the process by which agents select control laws. Participants adjusted their walking speed in a virtual environment in order to intercept approaching targets. Successful interception can be achieved with a constant bearing angle (CBA) strategy that relies on prospective information, or with a modified required velocity (MRV) strategy, which also includes predictive information. We manipulated the curvature of the target paths and the display condition of these paths. The curvature manipulation had large effects on the walking kinematics when the target paths were not displayed (informationally poor display). In contrast, the walking kinematics were less affected by the curvature manipulation when the target paths were displayed (informationally rich display). This indicates that participants used an MRV strategy in the informationally rich display and a CBA strategy in the informationally poor display. Quantitative fits of the respective models confirm this information-driven switch between the use of a strategy that relies on prospective information and a strategy that includes predictive information. We conclude that agents are able of taking advantage of available information by selecting a suitable control law.

Testing the role of expansion in the prospective control of locomotion.

The constant bearing angle (CBA) strategy is a prospective strategy that permits the interception of moving objects. The purpose of the present study is to test this strategy. Participants were asked to walk through a virtual environment and to change, if necessary, their walking speed so as to intercept approaching targets. The targets followed either a rectilinear or a curvilinear trajectory and target size was manipulated both within trials (target size was gradually changed during the trial in order to bias expansion) and between trials (targets of different sizes were used). The curvature manipulation had a large effect on the kinematics of walking, which is in agreement with the CBA strategy. The target size manipulations also affected the kinematics of walking. Although these effects of target size are not predicted by the CBA strategy, quantitative comparisons of observed kinematics and the kinematics predicted by the CBA strategy showed good fits. Furthermore, predictions based on the CBA strategy were deemed superior to predictions based on a required velocity (V (REQ)) model. The role of target size and expansion in the prospective control of walking is discussed.

Action-perception patterns in virtual ball bouncing: combating system latency and tracking functional validity.

How can we evaluate the spatio-temporal performance of virtual environments (VE) for research use? Here we show that end-to-end latency (ETEL) of VE can strongly damage users' perceptual and perceptuo-motor behaviors and that it can be considered to be the key factor for evaluating face and functional fidelity of a VE. We used a virtual ball-bouncing task as a paradigmatic example. Ball bouncing is known to exhibit attractive and repelling states whose localization in the racket cycle is sufficiently thin to be changed by small variations of ETEL. We first present a simple test-bed to measure the intrinsic ETEL of research-related VE systems. We then report results of a psychophysical ball-bouncing experiment in which ETEL was manipulated. While face validity (i.e., subjective experience) was maintained with relatively high values, the results reveal that the perception-action behavior (performance) was damaged with smaller ETEL values. These results call for action-perception variables in order to test the fidelity of VE systems.

Learning new perception-action solutions in virtual ball bouncing.

How do humans discover stable solutions to perceptual-motor tasks as they interact with the physical environment? We investigate this question using the task of rhythmically bouncing a ball on a racket, for which a passively stable solution is defined. Previously, it was shown that participants exploit this passive stability but can also actively stabilize bouncing under perceptual control. Using a virtual ball-bouncing display, we created new behavioral solutions for rhythmic bouncing by introducing a temporal delay (45 degrees -180 degrees ) between the motion of the physical racket and that of the virtual racket. We then studied how participants searched for and realized a new solution. In all delay conditions, participants learned to maintain bouncing just outside the passively stable region, indicating a role for active stabilization. They recovered the approximate initial phase of ball impact in the virtual racket cycle (half-way through the upswing) by adjusting the impact phase with the physical racket. With short delays (45 degrees , 90 degrees ), the impact phase quickly shifted later in the physical racket upswing. With long delays (135 degrees , 180 degrees ), bouncing was destabilized and phase was widely visited before a new preferred phase gradually emerged, during the physical downswing. Destabilization was likely due to the loss of spatial symmetry between the ball and physical racket motion at impact. The results suggest that new behavioral solutions may be discovered and stabilized through broad irregular sampling of variable space rather than through a systematic search.