Neural interface and experimental setup.

A) Surgeons implanted FINEs around the median, radial, and ulnar nerves of subjects S1 and S2[10]. Surgeons tunneled leads from the cuffs to a percutaneous exit site in the lateral upper arm. The percutaneous leads connected to an external nerve stimulator, which delivered pulses of electrical stimulation to the nerve. S1’s amputation is at the level of the wrist. S2’s amputation is at the proximal forearm. B) Force sensitive resistors were mounted to the subject’s hand prosthesis on the index, thumb, and middle finger. A flex sensor was mounted to the back of the hand to measure prosthetic aperture. The information transduced by these sensors was sent to a computer, which transformed them into appropriate stimulation patterns that were sent to the percutaneous leads. The subjects’ task was to identify either the size or the compliance of a foam block presented to the prosthetic hand, while the subject was blindfolded and wearing noise-cancelling headphones.