Harjo J. de Poel

Interlimb coupling strength scales with movement amplitude

The relation between movement amplitude and the strength of interlimb interactions was examined by comparing bimanual performance at different amplitude ratios (1:2, 1:1, and 2:1). For conditions with unequal amplitudes, the arm moving at the smaller amplitude was predicted to be more strongly affected by the contralateral arm than vice versa. This prediction was based on neurophysiological considerations and the HKB model of coupled oscillators. Participants performed rhythmic bimanual forearm movements at prescribed amplitude relations. After a brief mechanical perturbation of one arm, the relaxation process back to the initial coordination pattern was examined. This analysis focused on phase adaptations in the unperturbed arm, as these reflect the degree to which the movements of this arm were affected by the coupling influences stemming from the contralateral (perturbed) arm. The thus obtained index of coupling (IC) reflected the relative contribution of the unperturbed arm to the relaxation process. As predicted IC was larger when the perturbed arm moved at a larger amplitude than did the unperturbed arm, indicating that coupling strength scaled with movement amplitude. This result was discussed in relation to previous research regarding sources of asymmetry in coupling strength and the effects of amplitude disparity on interlimb coordination.

Don’t Rock the Boat: How Antiphase Crew Coordination Affects Rowing

It is generally accepted that crew rowing requires perfect synchronization between the movements of the rowers. However, a long-standing and somewhat counterintuitive idea is that out-of-phase crew rowing might have benefits over in-phase (i.e., synchronous) rowing. In synchronous rowing, 5 to 6% of the power produced by the rower(s) is lost to velocity fluctuations of the shell within each rowing cycle. Theoretically, a possible way for crews to increase average boat velocity is to reduce these fluctuations by rowing in antiphase coordination, a strategy in which rowers perfectly alternate their movements. On the other hand, the framework of coordination dynamics explicates that antiphase coordination is less stable than in-phase coordination, which may impede performance gains. Therefore, we compared antiphase to in-phase crew rowing performance in an ergometer experiment. Nine pairs of rowers performed a two-minute maximum effort in-phase and antiphase trial at 36 strokes min−1 on two coupled free-floating ergometers that allowed for power losses to velocity fluctuations. Rower and ergometer kinetics and kinematics were measured during the trials. All nine pairs easily acquired antiphase rowing during the warm-up, while one pair’s coordination briefly switched to in-phase during the maximum effort trial. Although antiphase interpersonal coordination was indeed less accurate and more variable, power production was not negatively affected. Importantly, in antiphase rowing the decreased power loss to velocity fluctuations resulted in more useful power being transferred to the ergometer flywheels. These results imply that antiphase rowing may indeed improve performance, even without any experience with antiphase technique. Furthermore, it demonstrates that although perfectly synchronous coordination may be the most stable, it is not necessarily equated with the most efficient or optimal performance.

Disentangling the Effects of Attentional and Amplitude Asymmetries on Relative Phase Dynamics

Attentional asymmetry in rhythmic interlimb coordination induces an asymmetry in relative phase dynamics, allegedly reflecting an asymmetry in coupling strength. However, relative phase asymmetries may also be engendered by an attention-induced difference between the amplitudes (and hence the preferred frequencies) of the limb movements. The authors conducted 3 experiments to dissociate those (not mutually exclusive) potential effects. Controlled manipulations of amplitude disparity and attentional focus, both alone and combined, revealed that variations in amplitude disparity had the expected effects, but produced evidence against the currently prevailing interpretation that attentional asymmetry affects the relative phase dynamics through an asymmetry in coupling strength. Implications of these findings are discussed vis-à-vis recent empirical findings and extant dynamical models.

Rowing Crew Coordination Dynamics at Increasing Stroke Rates

In rowing, perfect synchronisation is important for optimal performance of a crew. Remarkably, a recent study on ergometers demonstrated that antiphase crew coordination might be mechanically more efficient by reducing the power lost to within-cycle velocity fluctuations of the boat. However, coupled oscillator dynamics predict the stability of the coordination to decrease with increasing stroke rate, which in case of antiphase may eventually yield breakdowns to in-phase. Therefore, this study examined the effects of increasing stroke rate on in- and antiphase crew coordination in rowing dyads. Eleven experienced dyads rowed on two mechanically coupled ergometers on slides, which allowed the ergometer system to move back and forth as one ‘boat’. The dyads performed a ramp trial in both in- and antiphase pattern, in which stroke rates gradually increased from 30 strokes per minute (spm) to as fast as possible in steps of 2 spm. Kinematics of rowers, handles and ergometers were captured. Two dyads showed a breakdown of antiphase into in-phase coordination at the first stroke rate of the ramp trial. The other nine dyads reached between 34–42 spm in antiphase but achieved higher rates in in-phase. As expected, the coordinative accuracy in antiphase was worse than in in-phase crew coordination, while, somewhat surprisingly, the coordinative variability did not differ between the patterns. Whereas crew coordination did not substantially deteriorate with increasing stroke rate, stroke rate did affect the velocity fluctuations of the ergometers: fluctuations were clearly larger in the in-phase pattern than in the antiphase pattern, and this difference significantly increased with stroke rate. Together, these results suggest that although antiphase rowing is less stable (i.e., less resistant to perturbation), potential on-water benefits of antiphase over in-phase rowing may actually increase with stroke rate.

How visual information influences coordination dynamics when following the leader

Coordinating ones movements with others is an important aspect of human interactions. Regulating the distance to other moving agents is often necessary to achieve specific task goals such as in invasion sports. This study aimed to examine how distance regulation is mediated by different sources of information that are typically available when humans coordinate their actions to others. Participants followed a virtual leader that moved backwards and forwards, and were instructed to maintain the initial distance. In one condition, participants were presented with a life-size fully animated human avatar as the leader, displaying both segmental (limb motion) and global (optical expansion) motion information. In the other condition, participants had to follow an expanding and receding sphere in which segmental motion information was absent. Optical expansion rates revealed that participants regulated distance equally effective in both conditions. Given the phase relation and response times to direction changes however, the timing to the leader appeared to be more accurate in the avatar condition. These results provide support that forward-backward following can indeed be successfully mediated through global information, but that detection of segmental information allows for earlier tuning to another persons movement intentions.

Shaping decisions in volleyball An ecological approach to decision-making in volleyball passing

To extend research on decision-making in sport we addressed the choices volleyball-players are faced with in a simple volleyball pass-return task. We manipulated the distance that eight experienced volleyball players had to cover for successful ball passing, and mapped their passing technique (i.e., overhead or underhand) and ball return accuracy in a choice condition. Passing accuracy was then compared with conditions in which reception technique was imposed by instruction. When players were free to choose their technique the landing zone of the ball influenced the choice of technique: When a ball landed further away, the adoption of underhand technique increased, especially for balls that landed in front of the participants. Furthermore, in all conditions the accuracy of the pass decreased with increasing distance to be covered. These results are discussed vis-a-vis the idea that player behavior is shaped by affordances (i.e., possibilities for action). It is argued that to understand decision-making in dynamic sport situations we need to understand how players deal with competing affordances.

Individual contributions to (re-)stabilizing interpersonal movement coordination

Interpersonal movement coordination is characterized by stable coordination patterns. We examined the extent to which the two individuals within a dyad contributed to the stabilization of a shared coordination pattern. Within each dyad, the two participants coordinated rhythmic movements of their right lower arms in either in-phase or antiphase. We analyzed the responses to precisely controlled mechanical perturbations to one of the arms that disrupted the coordination pattern. Return to the original coordination pattern did not only involve phase adaptations in the perturbed arm, but in the unperturbed arm as well. Hence, the coupling between the companions was bidirectional and subserved the coordinative stability. Moreover, for both coordination patterns the interpersonal coupling was near symmetrical, with both actors (perturbed and unperturbed) contributing to the same extents to the restabilization of the coordination between them. The applied methodology provides a new entry point to examine asymmetries in interpersonal coupling, due to, for instance, social impairments, differences in social competence, or particular task setting.

Sync or separate? No compelling evidence for unintentional interpersonal coordination between Usain Bolt and Tyson Gay on the 100-meter world record race

In a recent observation article in Journal of Experimental Psychology: Human Perception and Performance (JEP:HPP; Varlet & Richardson, 2015) the 100-m sprint final of the World Championship in Athletics in Berlin of 2009 (i.e., the current world record race) was analyzed. That study reported occurrence of spontaneous, unintentional interpersonal synchronization between Usain Bolt and Tyson Gay, the respective winner and runner-up of that race. In the present commentary article, however, we argue that the results and conclusion of that study cannot be warranted because of methodological shortcomings. We addressed the same research question and reassessed the same race using an alternative data analysis method. These results revealed that as yet there is no sufficient ground to conclude that in the 100-m world record race synchronization occurred between Bolt and Gay. Yet, our reanalysis suggested that even at this very elite level the individual movement frequencies did seem to vary to such an extent that synchronization would theoretically still be possible, thereby providing incentives for further examination of potential unintentional synchronization in coactive sports.

Flexible Perception-Action Strategies: The Influence of Segmental and Global Motion Information on Follow-the-Leader Coordination

Interpersonal coordination in sports can be studied by examining interactions between agents. Evidently, individuals differ in their ability to interact with others (cf. ‘interact-ability’), which critically depends on their sensitivity to information for (inter-)action. Recently, we found that agents could access different information sources for the same task goal, yet it subtly affected temporal and spatial aspects of the interactive synchrony. The current study further examined what strategies agents adopt to deal with different types of information. Participants performed a follow-the-leader task in a virtual reality setting in several conditions. In the reference condition, a leader was presented as a back-and-forth walking animated avatar. In the other conditions, various aspects of motion information were either suppressed or emphasized. We emphasized movement of body segments using a point-light display. In other conditions we showed a mannequin (i.e. an avatar without moving limbs) with various combinations of the subtle, but potentially pertinent, lateral and vertical displacements that occur during gait. Another set of conditions showed different shapes (a mannequin, cylinder and sphere) that only displayed the optical size change corresponding to the back-and-forth displacement. Point-estimate relative phase revealed a tighter temporal synchrony when movements of body segments were shown. In contrast the virtual interpersonal distance was best maintained when only optical size change was displayed. These findings support the notion that a perception-action strategy is strongly shaped by its dynamic environment. Different skill levels of adopting such flexible behaviour may explain an individual’s interact-ability.

Influence of gait mode and body orientation on following a walking avatar

Regulating distance with a moving object or person is a key component of human movement and of skillful interpersonal coordination. The current set of experiments aimed to assess the role of gait mode and body orientation on distance regulation using a cyclical locomotor tracking task in which participants followed a virtual leader. In the first experiment, participants moved in the backward-forward direction while the body orientation of the virtual leader was manipulated (i.e., facing towards, or away from the follower), hence imposing an incongruence in gait mode between leader and follower. Distance regulation was spatially less accurate when followers walked backwards. Additionally, a clear trade-off was found between spatial leader-follower accuracy and temporal synchrony. Any perceptual effects were overshadowed by the effect of ones gait mode. In the second experiment we examined lateral following. The results suggested that lateral following was also constrained strongly by perceptual information presented by the leader. Together, these findings demonstrated how locomotor tracking depends on gait mode, but also on the body orientation of whoever is being followed.