Generalized Movement Representation in Haptic Perception

The extraction of spatial information by touch often involves exploratory movements, with tactile and kinesthetic signals combined to construct a spatial haptic percept. However, the body has many sensory surfaces that can move independently, giving rise to the source binding problem: when there are multiple tactile signals originating from sensory surfaces with multiple movements, are the tactile and kinesthetic signals bound to one another? We studied haptic signal combination by applying the tactile signal to a stationary fingertip while another body part (the other hand or a foot) or a visual target moves, and using a task that can only be done if the tactile and kinesthetic signals are combined. We found that both direction and speed of movement transfer across limbs, but only direction transfers between visual target motion and the tactile signal. In control experiments, we excluded the role of explicit reasoning or knowledge of motion kinematics in this transfer. These results demonstrate the existence of two motion representations in the haptic system—one of direction and another of speed or amplitude—that are both source-free or unbound from their sensory surface of origin. These representations may well underlie our flexibility in haptic perception and sensorimotor control.