LOCAL LEARNING OF INVERSE KINEMATICS IN HUMAN REACHING MOVEMENT

We have investigated how the paths of reaching movements improve with motor learning, and whether these improvements transfer to movements o ther than those in which subjects were trained. Planar reaching moveme nts were recorded in three groups moving in diagonal and lateral direc tions using a digitising table. All subjects made a number of reaching movements in a pre-test session. In the subsequent training phase of the experiment, one group of subjects was instructed to make lateral m ovements with as straight a path as possible; a second group made simi lar lateral movements following a straight line marked on the table; w hile a third group made diagonal movements, also following a marked li ne. All three groups were then tested making lateral and diagonal move ments, without the benefit of any marked lines. The straightness and v ariability of movement paths were analysed to investigate improvements in neural control following training. A significant group by directio n interaction indicated that movement straightness improved locally fo r the directions which were trained. Movement variability, in contrast , improved equally for all directions of movement. The results are con sistent with local learning of a neural inverse kinematics model used in movement planning and global learning of a neural forward kinematic s model used in movement execution.