Two Hands Perceive Better Than One

We often handle an object with both of our hands. The information from the two hands has to be combined to arrive at a single percept of the object. Research on multi-sensory perception has shown that redundant information between the senses is integrated such that the combined percept is more precise than either of the two individual inputs. However, while bimanual information can be redundant, it is not necessarily the case because both hands are usually touching different parts of the same object. To investigate whether there is a difference in precision of unimanual and bimanual information, we asked participants to discriminate stiffness unimanually as well as bimanually. Our results clearly show that bimanual perception of stiffness was more precise than unimanual perception. The precision of the bimanual percept was in agreement with the precision predicted from combining the two unimanual inputs in a statistical optimal fashion.