Effect of gravity on object manipulation during controlled collisions

In their everyday lives, humans perform collisions between hand-held objects and their surroundings, involving complex interactions in varied environments. To further analyze these interactions, we investigated the influence of body orientation and vision on the reference frame used to control grip force. To address this question, eighteen participants performed collisions tasks with and without vision, in three different body orientations representing different gravitational conditions. By analyzing the forces applied during these collisions tasks, more precisely the load force maximum and the grip force at contact, our results suggest a global tendency of the mechanisms underlying grip dynamics to rely on an allocentric reference frame. Contrarily, the study of the peak velocity and contact velocity revealed that kinematics is coded in an egocentric reference frame. Moreover, grip dynamics exhibits an adaptation along the task while it is not the case for kinematics. Finally, we argue that collisions are controlled based on a multimodal reference frame, so a frame that is influenced by several factors, such as our body orientation or vision.