Influence of reaching direction on visuomotor adaptation: an explorative study

Robotics is increasingly used in rehabilitation therapy of the hemiparetic arm after stroke. Several studies performed adaptation experiments to gain more insight in the underlying learning processes. In these studies adaptation during reaching movements in different directions is assessed. No information about influence of direction on the amount of learning to these separate directions is present. In this paper we assessed the effect of reaching direction on visuomotor learning. Forty healthy subjects performed 48 movements to five different directions during adaptation to a 30 degrees visuomotor rotation. The execution error was defined as the initial direction error at peak velocity and after 100 ms after onset of the movement. The amount of learning was defined as the difference between the start value and the end value of the execution error. A significant higher amount of adaptation in the movement towards the contralateral part of the body (-72) compared to reaching towards other directions was observed. When possible feedback and corrections mechanisms are taken into account; results indicate that subjects adapt most towards -72 direction and least towards -144 direction. Data of healthy elderly and stroke survivors would be essential to test whether observed results are present in these populations as well, which could have implications for motor relearning in rehabilitation therapy.