The combined effects of motor and social goals on the kinematics of object-directed motor action

Voluntary actions towards manipulable objects are usually performed with a particular motor goal (i.e., a task-specific object-target-effector interaction) and in a particular social context (i.e., who would benefit from these actions), but the mutual influence of these two constraints has not yet been properly studied. For this purpose, we asked participants to grasp an object and place it on either a small or large target in relation to Fitts' law (motor goal). This first action prepared them for a second grasp-to-place action which was performed under temporal constraints, either by the participants themselves or by a confederate (social goal). Kinematic analysis of the first preparatory grasp-to-place action showed that, while deceleration time was impacted by the motor goal, peak velocity was influenced by the social goal. Movement duration and trajectory height were modulated by both goals, the effect of the social goal being attenuated by the effect of the motor goal. Overall, these results suggest that both motor and social constraints influence the characteristics of object-oriented actions, with effects that combine in a hierarchical way.- This work was funded by the French National Research Agency (ANR-11-EQPX-0023) and also supported by European funds through the program FEDER SCV-IrDIVE. MFG was financed by the Region Hauts-de-France and the University of Lille. We are grateful to Anya Attou for her contribution to the data collection, Laurent Ott for his support in the computer programming of the study and Celia Moreira (mathematical researcher at FCUP-CMUP, University of Porto) for her helpful suggestions for statistical analysis