A Model for Bimanual Stiffness Perception and Action

During daily interactions with objects, we assess their mechanical properties to form perception and action. To date, perception and action in interaction with elastic objects have been tested only in unimanual interaction. A previous study examined perception of stiffness in unimanual right- or left-handed interactions and found that delayed force feedback causes stronger underestimation of stiffness when using the left hand. They speculated that this is a result of different processing delays when information is obtained using the left and right hand. Here, we set out to directly test this speculation during interactions with elastic objects with different hands sequentially. We used two robotic devices to present force feedback to participants in a virtual reality environment and recorded the position of the hand and the trajectories of their grip forces. Right- and left-handed participants probed pairs of virtual force fields with different hands and reported which had a higher level of stiffness. We assessed perception by fitting psychometric curves to the answers of participants, and we assessed action by comparing the grip force and load force trajectories during the interaction with each object. We expect to find differences in perception when the stiffness of elastic objects is probed with the left and right hand, and that adding delay to the force feedback of one hand will either increase or eliminate the difference of the existing natural delay between the two hands. Our findings will contribute to the development of controllers that will present force feedback to surgeons during robot-assisted surgery.