Robot-assisted intermanual transfer of handwriting skills.

We examined whether intermanual transfer of fine motor skills can be facilitated by training in a virtual environment. We focused on three types of assistance: visual - subjects could see a reference template on a computer screen - and two variants of haptic assistance. Subjects held a planar robot manipulandum and were required to write isolated cursive letters of an approximate size of 5 cm. Therefore, the task was similar to writing on a horizontal blackboard. The robot generated forces that were directed either towards the reference template (path guidance) or towards the reference trajectory (trajectory guidance). The training protocol consisted of three assisted exercise sessions on three consecutive days. Performance on the following day was tested to assess retention. After training, the improvement in trajectory shape was only significant in trajectory guidance and, to a lesser extent, visual guidance. Path guidance exhibited no significant improvement. These effects were substantially retained one day after the end of training. Similar effects were observed in shape variability. Furthermore, all training modalities caused a reduction in movement duration, but no significant differences were observed among groups. These results suggest that robot assistance may be beneficial for improving intermanual transfer, but inclusion of temporal information in the guidance strategy is essential for learning to take place.