Short CommunicationDoes the intention to communicate affect action kinematics?
Introduction
In contrast to other species, for human beings the possibility of communication is not confined to a limited number of signals. Every action can, in principle, become a communicative signal. The only pre-requisite is that the action is intended as communicative by the actor and recognized as such by the partner (Bara, in press). For example, the action of touching one’s earlobe – which is per se non-communicative – could become communicative in the context of a poker card game, when two players agree that touching the earlobe means: “Drop out the current hand”. An unexplored question is whether the imposition of a communicative meaning to an action affects action kinematics, i.e. how the action itself is implemented at the motor level.
Hierarchical models of action representation (e.g., Hamilton and Grafton, 2007, Wohlschläger et al., 2003) postulate different levels of motor control, relatively independent from each other. Common to different approaches is the idea of a progressive refinement, from an intentional level, to an object-goal level and finally to a kinematic level, which represents the actions required to achieve the goal. Finally, at a muscle level, the selected action is specified through the coordinated activation of muscles.
Whereas much is known about the organization of the lower levels, including selection of kinematic parameters, only a few studies have attempted to examine higher levels of motor control (e.g., Grafton & Hamilton, 2007). For example, little is known about how kinematic parameters (kinematic level) are influenced by the organized set of intention that one may entertain (intentional level) when performing the same object-directed action.
In the present study, we examine this issue by focusing on communicative intention. In principle every action can become communicative, but the question is to understand whether imposing a communicative intent might influence the parameterisation of the action kinematic. To answer this question we asked participants to perform the same goal-directed action in two different contexts that were operationalized through an individual task and a communicative task. In the individual task, participants were requested to reach towards, grasp and lift either a blue or a green spherical object according to one of five predetermined sequences. The communicative task was identical to the individual task except that participants executed the sequence with a communicative intent. Each of the sequences of blue and green spheres represented a different meaning in a sort of simplified Morse code. Participants were asked to select a meaning (and thus a sequence) and to communicate it to a partner by lifting the spheres in the predetermined order. Based on a conversion table, the partner had to interpret the meaning of the communicated sequence. Our interest was to ascertain whether the intention to communicate reflected on how the spheres were reached towards and grasped.
Section snippets
Participants
Ten subjects (7 women and 3 men, mean age 24 years) participated in the experiment. All were right-handed, reported normal or corrected-to-normal vision and were naïve as to the purpose of the study.
Stimuli
Stimuli were two plastic spheres (diameter: 4 cm, weight: 5 g) one blue and one green positioned on a black table at a 30 cm distance from a hand starting location along the midsagittal plane.
Apparatus
The working surface was a rectangular table (150 × 100 cm). The participant was seated on a height adjustable
Experiment 2
A possible objection against the interpretation given to the data obtained in Experiment 1 is that the presence of another person might be, per se, responsible for the differential pattern of results observed during the communicative condition. In other words, it could be argued that determining a different kinematic pattern is not the communicative intent underlying the action, but the mere presence of the co-experimenter. To exclude this alternative hypothesis in the present experiment we
General discussion
We set out to investigate whether the imposition of a communicative intent on an action might influence the action kinematic parameterization. Previous studies have already shown that intention mechanisms modulate actions kinematics (Ansuini et al., 2006, Becchio et al., 2008b, Castiello, 2003). For example, kinematics has been shown to be sensitive to prior intentions, i.e. intentions formed in advance and representing the end-goal of the action (Searle, 1983). Ansuini et al. (2006) found that
Acknowledgments
This work was supported by a Grant from the Italian Ministry of University and Research to UC. CB and BGB were supported by the Fondazione Cassa di Risparmio di Torino, Progetto Alfieri. The study had been approved by the local Ethics committee and written informed consent was obtained from each subject prior to participation.
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