Interactions between tactile and proprioceptive representations in haptics.

Neuroprosthetic limbs, regardless of their sophisticated motor control, require sensory feedback to viably interact with the environment. Toward that aim, the authors examined interrelationships between tactile and proprioceptive sensations. Through human psychophysics experiments, they evaluated error patterns of subjects estimating hand location in a horizontal 2-dimensional workspace under 3 tactile conditions. While tactile cues did not significantly affect the structure of the pattern of errors, touching the workspace reduced estimation errors. During neurophysiological experiments, a macaque grasped textured objects using 2 hand postures. Sensory coding showed dependence on both roughness of the manipulandum and posture. In summary, the authors suggest that tactile sensations underlying haptics are processed in a stable spatial reference frame provided by a proprioceptive system, and that tactile and proprioceptive inputs can be encoded simultaneously by individual cells. Such insights will be useful for providing stable, adaptive sensory feedback for neuroprosthetics.