Dextra

No, that's not the name of a new artificial sweetener. It's the name of a new type of prosthesis!

William Craelius of Rutgers University has invented an artificial hand system that allows normal thought-directed movement of up to three fingers. Read that again: The user executes normal, volitional movement of a prosthesis.

According to this Guardian article,

By recording the movement of muscles in the remaining part of the arm as a person thinks about moving their hand, Dextra can control up to three fingers. Different patterns of muscle movement correspond to different movements and, after a few minutes of calibration, the robotic hand is ready for action.

This article also, er, touches on Dextra. It states,

Dextra consists of a standard plastic socket and silicone sensor sleeve that encases an amputee's limb below the elbow. After a brief training period, operating the fingers is biomimetic, that is, it is done by normal volitional thinking, as if the user were commanding his natural fingers. Dextra relies on the fact that much of the musculo-tendon control structures that originally operated the fingers are still present and controllable by the user and can be tapped by the proper sensors. As long as the user remembers how to activate his phantom fingers, he can mentally command the new robot fingers. Thus far, users have been able to play slow piano pieces with Dextra, as demonstrated at Epcot Center for the Discover Magazine Innovation of the Year Award ceremony.

Let's look beyond the "wow" factor. This is pretty deep stuff. If you are controlling a prosthetic finger with your own mind, is it part of your body? If not, why is your natural finger part of your body? Where does your body end and the prosthesis begin?

Suppose instead that I don't have any prosthetic fingers, but am holding a pair of scissors in my natural hand. I control the scissors by volition, although not direct nerve stimulation (there is instead an indirect link through my skin). Is this situation the same, or different? Surely we wouldn't say the scissors are part of my body. So does that mean the nerve link is required? What counts as a direct nerve link?

Surely we aren't in the process of reducing a human body philosophically to the presence of proper neuromuscular junctions between components?

Of course not. A human is an integrated, emergent object. Reductionism will get you nowhere in this case and thus should be tossed out as the wrong tool for the job.

What we can say for certain is that the body is not the self. If I lose a hand in an accident, I am still Kim. Adding prosthetic fingers, or not adding them, doesn't change my nature. This may be easy to see intellectually, but is much harder to see deeply. After all, if we are not the body, there is little reason to judge people on appearance, to be concerned when we age or become ill, or to fear death. Let me know if you have never done any of these things because I want to become your student.