Communicative Interactions Improve Visual Detection of Biological Motion

Citation: Manera V, Becchio C, Schouten B, Bara BG, Verfaillie K ( Communicative Interactions Improve Visual Detection of Biological Motion Valeria Manera 0 Cristina Becchio 0 Ben Schouten 0 Bruno G. Bara 0 Karl Verfaillie 0 Sheng He, University of Minnesota, United States of America 0 1 Department of Psychology, Center for Cognitive Science, University of Turin , Turin , Italy , 2 Laboratory of Experimental Psychology, Department of Psychology, Katholieke Universiteit Leuven , Leuven , Belgium Background: In the context of interacting activities requiring close-body contact such as fighting or dancing, the actions of one agent can be used to predict the actions of the second agent [1]. In the present study, we investigated whether interpersonal predictive coding extends to interactive activities - such as communicative interactions - in which no physical contingency is implied between the movements of the interacting individuals. Methodology/Principal Findings: Participants observed point-light displays of two agents (A and B) performing separate actions. In the communicative condition, the action performed by agent B responded to a communicative gesture performed by agent A. In the individual condition, agent A's communicative action was substituted with a noncommunicative action. Using a simultaneous masking detection task, we demonstrate that observing the communicative gesture performed by agent A enhanced visual discrimination of agent B. Conclusions/Significance: Our finding complements and extends previous evidence for interpersonal predictive coding, suggesting that the communicative gestures of one agent can serve as a predictor for the expected actions of the respondent, even if no physical contact between agents is implied. - Funding: This research was supported by a grant from the Regione Piemonte, bando Scienze Umane e Sociali 2008, L.R. n. 4/2006, and by a grant from the Research Foundation Flanders (FWO), FWO G.0621.07. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Dancing a waltz, playing a piano duet, carrying a table together are all examples of joint activities requiring a considerable degree of interpersonal coordination. To successfully engage in these activities, actors must be able to direct their attention to where the interaction partner is attending (joint attention) [2,3] and to adjust their actions to those other persons choosing an appropriate complementary action to be performed at an appropriate time [4]. Time places serious constraints on joint actions and, as the time windows for coordination are often very narrow, actors must achieve a close temporal coordination for acting synchronously or in turns [5]. Similarly, to avoid bumping into one another or into an obstacle (e.g. when carrying an object together), they need to effectively distribute a common space and optimize movement paths. Under these circumstances, the possibilities for moving and for completing actions are jointly constrained [6]. As dynamical principles constrain the coordination of interpersonal movements, the actions of one agent can serve as predictors for the expected actions of the other agent [7]. Neri, Luu, and Levy [1] have indeed demonstrated that in the context of interacting activities requiring close-body contact such as fighting or dancing, the actions of one agent can be used to guide the processing of the actions performed by the other agent. Participants observed point-light displays of two fighters masked with noise dots scattered all over the screen. Visual detection of the target agent was better when the agent was embedded in a fighting sequence with the second agent acting synchronously as opposed to asynchronously, even though synchronization was irrelevant to the visual discrimination task. These findings suggest that implicit knowledge about the natural dynamics of human interaction guides the processing of motion patterns generated by the actions of individual agents. Because the actions of the two agents are dynamically coupled, the action of one agent can be used to predict the action of the other agent. In the present study, we investigated whether interpersonal predictive coding extends to interactive activities in which no physical contingency is implied between the movements of the interacting individuals. A paradigmatic case of social interaction in which the performance of the action of one agent is not physically contingent upon the performance of the partners action is communicative interaction. Consider the case of human pointing. Agent A points towards an object. Agent B turns her head to look at the object. It is only because we attribute to A the communicative intention to affect Bs behaviour for example, to inform B about the location of a certain object - that we expect As action to be followed by Bs response. The linkage between actions of the two agents is purely intentional [810] and only makes sense against the background of reciprocal communicative intention recognition [11]. In the present study we employed point-light displays to investigate whether communicative interaction influences visual discrimination of a human agent in a simultaneous masking detection task. Participants observed point-light displays of two agents (A and B) performing separate actions. In the communicative condition, the action performed by agent B (e.g., bend over to pick up something) responded to a communicative gesture performed by agent A (e.g., pointing to the object). In the individual condition, agent As communicative action was substituted with a non-communicative, unrelated action (e.g., jumping). We hypothesized that if information picked up from communicative interaction is used to predict the partners response, then observing As communicative gesture should enhance visual discrimination of agent B. Participants Participants were 23 undergraduate psychology students from the University of Leuven (5 male and 18 female, mean age = 21.1 years). They received course credits for their participation. All had normal or corrected-to-normal vision, had provided informed written consent, and were nave with respect to the purpose of the study. The study was approved by the Ethical Committee of the Faculty of Psychology of the University of Leuven and was conducted in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. Stimuli Stimuli consisted of two point-light figures, each consisting of 13 markers indicating the centre of the major joints of the actor (head, shoulders, elbows, wrists, hips, knees, and feet). Ten point-light stimuli were employed, five belonging to the communicative condition, five belonging to the individual condition. Stimuli for the communicative condition displayed a communicative interaction between two agents, with (...truncated)