title: Visuomotor adaptation to a visual rotation is gravity dependent.
abstract: Humans perform vertical and horizontal arm motions with different temporal patterns. The specific velocity profiles are chosen by the central nervous system by integrating the gravitational force field to minimize energy expenditure. However, what happens when a visuomotor rotation is applied, so that a motion performed in the horizontal plane is perceived as vertical? We investigated the dynamic of the adaptation of the spatial and temporal properties of a pointing motion during prolonged exposure to a 90° visuomotor rotation, where a horizontal movement was associated with a vertical visual feedback. We found that participants immediately adapted the spatial parameters of motion to the conflicting visual scene in order to keep their arm trajectory straight. In contrast, the initial symmetric velocity profiles specific for a horizontal motion were progressively modified during the conflict exposure, becoming more asymmetric and similar to those appropriate for a vertical motion. Importantly, this visual effect that increased with repetitions was not followed by a consistent aftereffect when the conflicting visual feedback was absent (catch and washout trials). In a control experiment we demonstrated that an intrinsic representation of the temporal structure of perceived vertical motions could provide the error signal allowing for this progressive adaptation of motion timing. These findings suggest that gravity strongly constrains motor learning and the reweighting process between visual and proprioceptive sensory inputs, leading to the selection of a motor plan that is suboptimal in terms of energy expenditure.
authors.affiliation: Centre of Space Bio-medicine, University of Rome Tor Vergata, Rome, Italy; Laboratory of Neuromotor Physiology, IRCCS Santa Lucia Foundation, Rome, Italy;
authors.forename: Simone
authors.initials: S
authors.lastname: Toma
authors.affiliation: Department of Robotics, Brain and Cognitive Sciences, Fondazione Istituto Italiano di Tecnologia, Genoa, Italy;
authors.forename: Alessandra
authors.initials: A
authors.lastname: Sciutti
authors.affiliation: Unité 1093, Cognition, Action et Plasticité Sensorimotrice, Institut National de la Santé et de la Recherche Médicale (INSERM), UFR STAPS, Dijon, France; and.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Papaxanthis
authors.affiliation: Department of Robotics, Brain and Cognitive Sciences, Fondazione Istituto Italiano di Tecnologia, Genoa, Italy; Unité 1093, Cognition, Action et Plasticité Sensorimotrice, Institut National de la Santé et de la Recherche Médicale (INSERM), UFR STAPS, Dijon, France; and Institut Universitaire de France (IUF), Université de Bourgogne, Dijon, France thierry.pozzo@u-bourgogne.fr.
authors.forename: Thierry
authors.initials: T
authors.lastname: Pozzo
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001132:Arm / Q000502:physiology; D025461:Feedback, Physiological; D005260:Female; D006112:Gravitation; D006801:Humans; D008297:Male; D009039:Motion Perception; D011597:Psychomotor Performance; D012399:Rotation
keywords: internal model of gravity; motor planning; sensorimotor adaptation; visual vertical