Gentilucci1,2* Abstract Social Requests and Social Affordances: How They Affect the Kinematics of Motor Sequences during Interactions between Conspecifics Francesca Ferri1, Giovanna Cristina Campione1, Riccardo Dalla Volta1, Claudia Gianelli1, Maurizio 1 Department of Neuroscience, University of Parma, Parma, Italy, 2 Brain Center for Social and Motor Cognition, Italian Institute of Technology, Parma, Italy The present study aimed at determining whether and what factors affect the control of motor sequences related to interactions between conspecifics. Experiment 1 demonstrated that during interactions between conspecifics guided by the social intention of feeding, a social affordance was activated, which modified the kinematics of sequences constituted by reaching-grasping and placing. This was relative to the same sequence directed to an inanimate target. Experiments 2 and 4 suggested that the related-to-feeding social request emitted by the receiver (i.e. the request gesture of mouth opening) is prerequisite in order to activate a social affordance. Specifically, the two experiments showed that the social request to be fed activated a social affordance even when the sequences directed towards a conspecific were not finalized to feed. Experiment 3 showed that moving inside the peripersonal space of a conspecific, who did not produce any social request, marginally affected the sequence. Finally, experiments 5 and 6 indicated that the gaze of a conspecific is necessary to make a social request effective at activating a social affordance. Summing up, the results of the present study suggest that the control of motor sequences can be changed by the interaction between giver and receiver: the interaction is characterized by a social affordance that the giver activates on the basis of social requests produced by the receiver. The gaze of the receiver is a prerequisite to make a social request effective. Citation: Ferri F, Campione GC, Dalla Volta R, Gianelli C, Gentilucci M (2011) Social Requests and Social Affordances: How They Affect the Kinematics of Motor Sequences during Interactions between Conspecifics. PLoS ONE 6(1): e15855. doi:10.1371/journal.pone.0015855 Editor: Manos Tsakiris, Royal Holloway, University of London, United Kingdom Received August 30, 2010; Accepted November 25, 2010; Published January 24, 2011 Copyright: 2011 Ferri et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by MUR (Ministero dell’Universita` e della Ricerca). 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. * E-mail: gentiluc@unipr.it Introduction According to the Fitts’ law [1] the duration of movements directed to a target lengthens, and in general the kinematics of transitive actions (i.e. acted upon an object, [2–5]) slow down, with an increasing index of movement difficulty. The index of difficulty is directly proportional to movement amplitude and inversely proportional to target size. Increasing movement difficulty induces greater accuracy during movement execution. However, other factors can affect accuracy during action control. Marteniuk et al. [4] found that the final phase of the reaching-grasping of an object lengthened when the successive movement was placing it into a container, as compared to less accurate movements, like throwing it. The data of other kinematic studies [6–8] confirmed that the overall intention of an action sequence could induce changes in the kinematics of even the initial actions. In other words, the overall intention can influence the degree of accuracy of each action of a sequence. These findings are in accordance with data of single neuron recording studies: Fogassi, Ferrari, Gesierich, Rozzi, Chersi and Rizzolatti [9] recorded neurons in monkey parietal cortex that discharged when the animal executed the grasping of a piece of food in order to bring it to its mouth. In contrast, they did not discharge when the second action was placing it into a container beside the monkey’s mouth. The authors proposed that these neurons code the overall intention of the sequence (i.e. they code ‘‘why’’ an object is grasped). The above cited studies [2–8] indicate that the affordances of an object, i.e. the types and motor patterns of interaction with an object (for a review see [10]), also depend on the final intention of actions, and, broadly speaking, on the context in which the actions are executed. On the basis of this idea, Loveland [11] proposed other two types of affordances: the culturally selected affordances and the social affordances. The culturally selected affordances reflect preferred but not necessary interactions. They are due to participation with other people in a shared cultural milieu that predisposes individuals to use objects in particular ways. The social affordances reflect the meaning of human activity, like for example request gesture, which indicates to other individuals a required type and pattern of interaction. The activation of social affordances is typical of interactions between conspecifics. Becchio, Sartori, Bulgheroni and Castiello [12] reported that interacting with a conspecific by a sequence constituted by the actions of reaching-grasping an object and placing it on the hand of a conspecific induces variation in the kinematics of the actions, as compared to the same sequence directed to a container. Specifically, during the reach-to-grasp action they observed a decrease in the maximal finger aperture and peak grip closing velocity when interacting with the conspecific. The authors PLoS ONE | www.plosone.org 1 January 2011 | Volume 6 | Issue 1 | e15855