The role of slip motion for the control of reaching movements

Hand reaching is a complex task that requires the integration of multiple sensory information from muscle, joints and the skin, and internal model of the motor command (Gardner and Johnson 2013). Whenever we touch a surface and we slide our fingertip on it, texture orientation and slip motion provide information about the path length (Moscatelli, Naceri, and Ernst 2014), and about the direction of the hand trajectory (Moscatelli, Bianchi et al. 2019). In an ongoing study, we use an innovative haptic device to physically decouple slip motion and hand movements during a reaching task (Ciotti, Ryan et al., 2021). Participants slid their fingertip on the lubricated surface of the device towards a visual target. The position of the contact plate was continuously updated with the hand position multiplied by a gain parameter. By changing the value of the gain across trials, it was possible to produce different combinations of slip motion and hand motion. We evaluated the systematic changes in the hand velocity profile and the motion path depending on slip motion stimuli. Our results support our previous findings that the perceived movement of the hand is a weighted average of cutaneous and kinesthetic cues.