Realism might not matter for next-gen prostheses

Both of DARPA's Revolutionizing Prosthetics programsâ''Deka's 2007 "Luke arm" and the larger 2009 projectâ''are working on a cosmesis for their bionic arm; a flesh-colored, hand-shaped, natural looking glove to disguise the alloy and plastic underneath. Theyâ''ve gone to great lengths to make it look like the real thing. At Deka, I saw a silicon hand that had been painstakingly hand-painted from the inside out to keep the paint from ever rubbing off. The paint job convincingly mimics veins, knuckles and tendons. The realistic nails are added on later, the fingertips felt real enough to creep me out, and the thing felt like a real (if cold, dead) hand.

Todd Farrington, a software engineer at Deka, has been wearing two classic hook and cable prosthetic arms since he was electrocuted at the age of 12. He still has his arms above the elbow. We share the same hunt-and-peck approach to keyboard use, but thereâ''s an important difference between us: he can write poetry. Farrington is eager to start test piloting the Luke arm.

But Farrington and another Deka test pilot, Chuck Hildreth, made it clear to me that making the new arm look real was the last thing on their minds.

Farrington says that cosmeses are important to people who have recently lost limbs. They want to get back a feeling of normalcy. But within a few years, Farrington says, looking normal stops being the most important thing. â''Theyâ''re only going to care about functionality,â'' he says. Thatâ''s one of the many reasons why todayâ''s prosthetic limbs, skin-color-matched and hand-shaped though they may be, end up collecting dust in the closet instead of on the patient.

The problem with cosmeses is that while they look pretty, especially Dekaâ''s $10,000 model, they impede the function of the prosthesis beneath. In fact, Farringtonâ''s own prosthetics illustrate his point: â''Face it, itâ''s never really going to look real,â'' he says. â''Itâ''s not going to be convincing.â'' So even though his right arm is a pale peach-colored plastic to approximate his skin, when it was time to get the left arm, Farrington called the prosthetist and told him to go with the less expensive carbon fiber. He pulls up his sleeve and shows me silver-black carbon fiber, shimmering with a pattern of subtle scales. I ask him if he would wear a cosmesis over the Luke arm. He grins and shakes his head quickly.

I think while these next-gen arms were being conceived, the idea of the cosmesis came and went. When you see an arm that moves as naturally and gracefully as the real thing, you stop caring if itâ''s got skin. Itâ''s a weird little cognitive dissonance trick your brain plays on you: last year at DARPATech, I met Jesse Sullivan, who was wearing the Revolutionizing Prosthetics 2009 Proto-2 arm. Heâ''s got it wired into his reinnervated pectoral muscles, so when he wants to move his hand, he doesnâ''t have to stop and think about it. He just moves his hand. After about a minute, my brain could not compute the prosthetic hand/natural movement paradox and just gave up. My primate brain could not keep up, and so against my will, I perceived Jesse as having a fully functioning arm, covered by a robot suit.

Now that weâ''re not giving people hooks and claws anymore, thereâ''s no need to be so insistent with the camouflage. With the Blade Runner making headlines, it seems like everyoneâ''s starting to get used to the idea of being modded. Somehow, an amputee just isnâ''t all that pitiable when he can outrun you and everyone you know.


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