Project summary This small research grant will allow us to study the only known individual with a congenital lack of somatosensory afferents (KS) and to compare her motor performance, unconscious body schema, and conscious body image with those of IW, an individual with the rare condition of acquired somatosensory loss as well as to controls. KS lives in the United States and IW lives in Britain and we propose to study both individuals in the fully equipped laboratory of co-PI Chris Miall in Birmingham, UK. In both participants motor nerve function is intact, allowing us to investigate motor coordination through its effector body parts, working without peripherally originating haptic feedback. Funds are requested to support travel and the study of control participants for comparison. The importance of large-fiber sensory input for creating a body schema that in turn allows for the rapid and largely unconscious production of movement will be placed in stark relief by KS and IW. Two distinct solutions to a loss of such input, one based on a congenital lack and one on an acquired loss, will be identified. In the former case, a degree of automaticity based on enhanced visual proprioception is expected whereas movement in the face of acquired deafferentation is expected to depend on conscious and slow visual perception combined with cognitive oversight. Thus, our working hypothesis is that IW uses visual perception, cognitively demanding motor planning, and conscious body image to move in a consciously supervised and minimally automated manner. In contrast, we hypothesize that KS uses visual proprioception, an automated substitution of visual information for somatosensory proprioception, to support a body schema that automatically supports motor planning and execution. Aim 1 will test our hypotheses by asking KS and IW to make repeated iterations of previously learned movements, with and without cognitive load, and to learn new movements that range in complexity. In Aim 2, the unconscious body schema of IW and KS will be interrogated through reach estimation and testing for peri-personal perceptual facilitation. Finally, in Aim 3, we will directly compare KS?s and IW?s conscious body images. Results from the proposed experiments will uncover for the first time the relative roles of large-fiber somatosensory information in setting up and then maintaining for decades, sensorimotor function, body schema and body image.