Influence of visual information on bimanual haptic manipulation

The coordination of the upper limbs has been shown to be beneficial for post-stroke treatment. In virtual reality based rehabilitation, bimanual exercises can be performed by exploiting haptic rendering techniques that allow object manipulation with two haptic devices. Haptic interaction generally involves spherical end-effectors with invariant shapes. Furthermore, the position of the end-effectors can only be sensed haptically after object contact, which impacts the ability to determine the real position of the end effector and dynamically manipulate the object. The present study sought to examine whether additional visual information regarding the penetration of the wrists into the virtual object (i.e., the color and shape of the spheres changed according to the level of force exerted by the subject) leads to improved bimanual task performance in a virtual environment. To this end, six neurologically healthy participants performed an object manipulation task with haptic feedback (haptic condition) and with haptic feedback as well as additional visual cues (haptic+visual condition). Results demonstrated that interlimb coordination was enhanced during the haptic+visual condition. It is speculated that the presence of visual information provides a more natural way for individuals to exploit inter-limb coordination synergies, and may have useful implications for VR game development and post stroke rehabilitation protocols.