Detecting Deception in Movement: The Case of the Side-Step in Rugby

Abstract

Although coordinated patterns of body movement can be used to communicate action intention, they can also be used to deceive. Often known as deceptive movements, these unpredictable patterns of body movement can give a competitive advantage to an attacker when trying to outwit a defender. In this particular study, we immersed novice and expert rugby players in an interactive virtual rugby environment to understand how the dynamics of deceptive body movement influence a defending player’s decisions about how and when to act. When asked to judge final running direction, expert players who were found to tune into prospective tau-based information specified in the dynamics of ‘honest’ movement signals (Centre of Mass), performed significantly better than novices who tuned into the dynamics of ‘deceptive’ movement signals (upper trunk yaw and out-foot placement) (p<.001). These findings were further corroborated in a second experiment where players were able to move as if to intercept or ‘tackle’ the virtual attacker. An analysis of action responses showed that experts waited significantly longer before initiating movement (p<.001). By waiting longer and picking up more information that would inform about future running direction these experts made significantly fewer errors (p<.05). In this paper we not only present a mathematical model that describes how deception in body-based movement is detected, but we also show how perceptual expertise is manifested in action expertise. We conclude that being able to tune into the ‘honest’ information specifying true running action intention gives a strong competitive advantage.

Dissociated Representations of Deceptive Intentions and Kinematic Adaptations in the Observer's Motor System

“…These effects were independent from the object weight. Providing exaggerated body-related cues that induce others to make incorrect action predictions and minimizing or delaying informative postural cues are fundamental aspects of effective deception (Brault et al 2010;Brault et al 2012). Here, we showed that these alterations of movement kinematics succeeded in blurring the observer's sensitivity in predicting object weight by observing reaching-to-grasp and lifting movements.…”

“…Conversely, the ANOVA performed on the lifting duration revealed a significant interaction between weight and action condition (F(2,30) = 4.77, P = 0.016, η P 2 = 0.241), because the truthful lifting of heavy objects lasted less than the lifting in all other types of videos (all P < 0.048). Thus, the lifting of heavy objects was delayed for both deceptive and deceived actions as compared to truthful lifting movements, suggesting that, even if this temporal kinematics parameter can be intentionally altered by deceptive intentions (Brault et al 2012;Tidoni et al 2013), it cannot dissociate between intentional deception and kinematics adjustment behavior (Fig. 2).…”

Expert players accurately detect an opponent’s movement intentions through sound alone.

“…This highlights the importance of the unfolding pattern of the attacker's movements in informing and guiding choices about when and how to act in an anticipatory way (Brault et al, 2012).…”

“…Through these mechanisms it is hypothesised that expert sports players are better able to predict whether a basketball shot will result in a basket (Aglioti, Cesari, Romani, & Urgesi, 2008), detect when an attacker is trying to use his/her movements to deceive an opponent in rugby (Brault et al, 2012) and to anticipate deceptive action in soccer (Tomeo, Cesari, Aglioti, & Urgesi, 2012).…”

“…Interestingly, this expertise-dependent advantage was not found in a similar ball-curve perception only task in which participants simply had to judge, ahead of time, whether a free-kick would result in a goal or not (Craig et al, 2009). This suggests that the effects of skill-based actioncapabilities on perception may be more strongly manifested when perception is coupled to action ACTION ANTICIPATION THROUGH ITS SOUND ALONE 6 6 and the task requires participants to act on the perceptual information in a manner appropriate to their domain of expertise (Brault et al, 2012;Correia et al, 2012;Dessing & Craig, 2010;Watson et al, 2011). This question was explored here by having novice and expert basketball player perform a more ecologically-valid action-response task (virtual full-body blocking of a perceived attacking player -expertise specific), in addition to a generic perception-action task (moving a slider in the perceived direction of the attacking player -non-expertise specific).…”