Is a robot needed to modify human effort in bimanual tracking?

Robotic bimanual training can benefit from understanding how to modify human motor effort in bimanual tasks. We addressed this issue by carrying out a study to investigate whether and how penalizing the use of one hand could alter the hands' effort distribution. Actuated haptic perturbations and alterations of the visual feedback of the right hand were tested on a bimanual tracking task with 16 healthy right-handed participants. For each feedback modality (haptic or visual), both a disturbance and a perturbation requiring additional effort from the right hand were implemented. The results showed that the participants were able to adjust to these four perturbations, and perceived them correctly as something that disturbed the dominant hand. Contrary to our expectations, the bimanual effort distribution changes induced by the haptic perturbations were not uniform across subjects. However, the visual disturbance induced most participants to use only their unperturbed left hand (with only 2/16 participants reporting a different behaviour). This suggests that a visual disturbance could be used to alter the effort distribution among the two hands. Clinical validation of these findings on hemiplegic patients may help simplify the design of robotic training interfaces.