Abstract
During the execution of a reaching movement, small errors in the trajectory are exploited to improve the following movements. Motor adaptation studies often investigate this error-driven learning by perturbing movements and evaluating the after-effect. A blocked design is usually adopted, where the same type and parameterization of visual or haptic distortion are applied to hand movements repetitively, such as visual disturbances and position- or velocity-dependent and even more complicated force-fields. The general finding is that, over a sequence of trials, subjects show an incremental learning, by generating a movement that roughly mirrors the perceived distortion. However, perturbations experienced during daily life frequently and randomly change in space, time and nature, hampering the adaptation in subsequent movements. The way the brain deals with such perturbations, in case of successful adaptation, is still unknown and under investigated. In this work, we hypothesized that the nervous system can develop a specific motor learning in response to space-variant perturbations. During training, participants wore a head-mounted display and were asked to grasp the puck of a digitizing board recording the hand movement on the horizontal plane during a reaching task. In a virtual reality scenario, they had to move a cursor toward a target presented in one of three possible directions, randomly selected, at the same distance from the starting position, corresponding to the participant’s hand position at the beginning of each trial. Participants were tested for adaptation to a position-dependent sinusoidal visual perturbation of the cursor representing the hand movement, in a trial-by-trial paradigm. Preliminary results show that people can adapt to a space-variant visual feedback distortion, by developing a motor strategy proportional to a combination of the perturbation parameters and mirroring its overall effect. This can be interpreted as a strategy-specific motor learning.