Grip selection without tool knowledge: end-state comfort effect in familiar and novel tool use.

A well-known phenomenon for the study of movement planning is the end-state comfort (ESC) effect: When they reach and grasp tools, individuals tend to adopt uncomfortable initial hand postures if that allows a subsequent comfortable final posture. In the context of tool use, this effect is modulated by tool orientation, task goal, and cooperation. However, the cognitive bases of the ESC effect remain unclear. The goal of this study was to determine the contribution of semantic tool knowledge and technical reasoning to movement planning, by testing whether the ESC effect typically observed with familiar tools would also be observed with novel tools. Twenty-six participants were asked to reach and grasp familiar and novel tools under varying conditions (i.e., tool's handle downward vs. upward; tool transport vs. use; solo vs. cooperation). In our findings, the effects of tool orientation, task goal and cooperation were replicated with novel tools. It follows that semantic tool knowledge is not critical for the ESC effect to occur. In fact, we found an "habitual" effect: Participant adopted uncomfortable grips with familiar tools even when it was not necessary (i.e., to transport them), probably because of the interference of habitual movement programming with actual movement programming. A cognitive view of movement planning is proposed, according to which goal comprehension (1) may rely on semantic tool knowledge, technical reasoning, and/or social skills, (2) defines end-state configuration, which in turn (3) calibrates beginning-state comfort and hence the occurrence of the ESC effect.

Joint Perception of a Shared Object: A Minimalist Perceptual Crossing Experiment.

The minimalist perceptual crossing paradigm has emphasized the essential role of interpersonal dynamics on social understanding. Within the particular case of minimalist interaction, it has been argued that interpersonal processes can constitute social cognition, at least partially, which calls for a paradigm shift in social cognition studies. In this paper, we review several perceptual crossing experiments and their theoretical implications, and propose an original experiment to go beyond strictly dyadic interactions. Whereas past experiments have used objects as distracters of dyadic interaction, our experiment aims at integrating objects themselves as the goal of interpersonal coordination. We asked 24 subjects to participate in a minimalist perceptual crossing experiment where they had to decide, based on their on-line interaction in a one-dimensional digital space, which of the objects they perceived was also perceptible by their partner. The main results suggest that the mutual awareness of a shared object (SO) arises from the quality of sensorimotor coordination between the partners. Indeed, the presence of a SO acts as a simultaneous affordance that attracts and structures individual perceptive activities, giving both partners the opportunity to co-construct a shared world where their respective actions make sense. We discuss our results by way of an enactive account of social cognition, taking the joint perception of a SO as a first step to account for joint attention.