Antoine H. P. Morice

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°–180°) 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°, 90°), the impact phase quickly shifted later in the physical racket upswing. With long delays (135°, 180°), 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.

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.

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.

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 (VREQ) model. The role of target size and expansion in the prospective control of walking is discussed.

AGE-RELATED DECLINE IN SENSORY PROCESSING FOR LOCOMOTION AND INTERCEPTION

The ability to control locomotion through the environment and to intercept, or avoid objects is fundamental to the survival of all locomotor species. The extent to which this control relies upon optic flow, visual direction cues or non-visual sensory inputs has long been debated. Here we look at the use of sensory information in young and middle-aged participants using a locomotor-driven interceptive task. Both groups of participants were asked to produce forward displacements in more or less impoverished environments by manipulating a joystick and to regulate, if necessary, their displacement velocity so as to intercept approaching targets. We show that the displacements produced by the middle-aged participants were more nonlinear in comparison with young participants. The errors in the middle-aged group can be accounted for by a constant bearing angle (CBA) model that incorporates a decrease in the sensitivity of sensory detection with advancing age. The implications of this study to a better understanding of the mechanisms underlying the detection of the rate of change in bearing angle are discussed.

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 Wieringens 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.

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

ABSTRACT 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.

An Affordance-Based Approach to Visually Guided Overtaking

When an automobile driver overtakes a lead vehicle while avoiding oncoming traffic, does he or she do so with reference to the limits of his or her car? We investigated overtaking from the perspective of the theory of affordances. We define the overtake-ability affordance as a ratio of the minimum satisfying velocity required for safe overtaking (MSV) to the maximum velocity of the drivers car (Vmax). Two groups of participants performed overtaking maneuvers, if deemed possible, by driving either a slow (Vmax = 25 m/s) or a fast (Vmax = 32.5 m/s) virtual car in overtaking situations constrained by 14 values of MSV. For any given MSV condition, participants in the fast car group were more likely to attempt an overtaking maneuver. However, when MSV was expressed in intrinsic units as a ratio of Vmax for both groups, the frequency of overtaking was not significantly different across groups. Furthermore, overtaking frequency dropped to near 0% for both groups when MSV exceeded Vmax. In accordance with the affordance-based framework (Fajen, 2007), our results suggest that participants select their overtaking maneuvers by perceiving an overtake-ability affordance.

Interdisciplinary Research: A Promising Approach to Investigate Elite Performance in Sports

ABSTRACT While the call for interdisciplinary studies has been loud and clear over the last decade or so, the number of interdisciplinary publications in sport sciences is rather limited. One of the reasons for this scarcity is the complexity of the research process itself. Still, the combination and integration of information from different scientific disciplines seems to be important to better explain how elite performance comes about. In this article, we focus on this issue and discuss the advantages of interdisciplinary research for understanding how elite athletes are able to achieve such high-proficiency levels. The first section provides an overview of the studies that investigated elite performance in sports. In the second section, we focus on the issue of interdisciplinarity and illustrate how the ecological–dynamical approach and the concept of dimensional reduction can be used to explain how elite performers cope with the complex nature of sport skills. In the last section, we present a research outline and some practical considerations that can be helpful for researchers who aim to study sport skills from an interdisciplinary perspective.

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 (Vmax) of the driven car. In this definition, however, the maximum acceleration (Amax) 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 Amax of the car. Method: Two groups of nine drivers drove cars differing in their Amax. 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/Vmax and MSA/Amax, 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/Amax 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/Amax variables in order to suggest perceptually relevant overtaking solutions.