The relativity of reaching: Motion of the touched surface alters the trajectory of hand movements
Colleen P. Ryan,
Simone Ciotti,
Priscilla Balestrucci,
Antonio Bicchi,
Francesco Lacquaniti,
Matteo Bianchi,
Alessandro Moscatelli
Affiliations
Colleen P. Ryan
Department of Systems Medicine and Centre of Space Biomedicine, University of Rome Tor Vergata, 00133 Rome, Italy; Laboratory of Neuromotor Physiology, Santa Lucia Foundation IRCCS, 00179 Rome, Italy
Simone Ciotti
Laboratory of Neuromotor Physiology, Santa Lucia Foundation IRCCS, 00179 Rome, Italy; Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, 56122 Pisa, Italy
Priscilla Balestrucci
Laboratory of Neuromotor Physiology, Santa Lucia Foundation IRCCS, 00179 Rome, Italy
Antonio Bicchi
Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, 56122 Pisa, Italy; Istituto Italiano di Tecnologia, 16163 Genova, Italy
Francesco Lacquaniti
Department of Systems Medicine and Centre of Space Biomedicine, University of Rome Tor Vergata, 00133 Rome, Italy; Laboratory of Neuromotor Physiology, Santa Lucia Foundation IRCCS, 00179 Rome, Italy; Corresponding author
Matteo Bianchi
Research Centre E. Piaggio and Department of Information Engineering, University of Pisa, 56122 Pisa, Italy
Alessandro Moscatelli
Department of Systems Medicine and Centre of Space Biomedicine, University of Rome Tor Vergata, 00133 Rome, Italy; Laboratory of Neuromotor Physiology, Santa Lucia Foundation IRCCS, 00179 Rome, Italy; Corresponding author
Summary: For dexterous control of the hand, humans integrate sensory information and prior knowledge regarding their bodies and the world. We studied the role of touch in hand motor control by challenging a fundamental prior assumption—that self-motion of inanimate objects is unlikely upon contact. In a reaching task, participants slid their fingertips across a robotic interface, with their hand hidden from sight. Unbeknownst to the participants, the robotic interface remained static, followed hand movement, or moved in opposition to it. We considered two hypotheses. Either participants were able to account for surface motion or, if the stationarity assumption held, they would integrate the biased tactile cues and proprioception. Motor errors consistent with the latter hypothesis were observed. The role of visual feedback, tactile sensitivity, and friction was also investigated. Our study carries profound implications for human-machine collaboration in a world where objects may no longer conform to the stationarity assumption.
