Weird, Wonderful, Fascinating Limbs
Wandering Wednesdays #36
Tentacles, spikes, hands with two thumbs — prosthetic limbs do not need to look like real ones after all.
This is Kelly Knox — a British model and disability-rights advocate — posing with a prosthetic limb unlike any other. Ms Knox was born with her left arm missing from the elbow down. From the point her arm terminates, dozens of vertebrae-like structures extend to form a long, sinuous tentacle.
The limb is certainly striking. It is apparently dextrous, too. Ms Knox can control its movements via pressure sensors in her shoes, which connect to the limb wirelessly. Artificial tendons tighten or loosen, allowing the tentacle to reach and grasp.
This limb was designed by Sophie de Oliveira Barata, an artist, and Dani Clode, a designer and engineer. Although this is an art piece, it is one inspired by some intriguing recent developments in neuroscience that suggest prosthetic limbs don’t need to look or behave like the biological ones they replace.
How do we know ‘our’ body? Embodiment is the way in which our brain identifies with the body it is located in, and determines the borders of what counts as ‘self’ and what counts as ‘other’.
Sometimes, embodiment can go wrong. Most amputees experience the continued presence of their missing limbs, often for years after they have been removed. This ‘phantom limb syndrome’ (PLS) demonstrates that the brain’s idea of the body’s boundaries does not always match physical reality.
But scientists’ understanding of embodiment has started to change. In a series of experiments recently, Dr Tamar Makin, a neuroscientist who runs the Plasticity Lab at the University of Cambridge, discovered that the brain ‘places prosthetics in a category entirely of their own, clearly distinct from normal limbs or tools like brushes’. Meaning that whether a prosthetic is embodied or not does not have much to do with whether it looks like a biological arm or leg.
This has implications for the design of prosthetics. One is to open it up to all sorts of innovation in materials, colour and form. This is where Ms de Oliveira Barata comes in. She runs the Alternative Limb Project (ALP), a British studio that makes custom prosthetics.
And if a prosthetic need not mimic the limb it is replacing, then perhaps prosthetics can be more than just replacements? Ms Clode is an expert in the design of robotic prostheses controlled by artificial tendons. She is keen to explore the possibility of augmenting existing bodies with new capabilities, making prosthetics ‘a technology that could be of use to everybody, not just amputees’. To that end, she has designed the ‘Third Thumb’, a small and robust prosthetic digit. Controlled, like Ms Knox’s vine-arm, by pressure sensors in a pair of shoes, the thumb can be used to replace a missing one. But it can also be added to an intact hand on the opposite side from its existing, biological thumb.
Having two thumbs ‘extends what the human hand can do in surprising ways,’ says Ms Clode. Like holding an object and manipulating at the same time, such as peeling a banana or opening a soft-drink bottle one-handed.
Modern Dance — Someday, in the not too distant future, an adventurous classical dancer may mimic Shiva, the cosmic dancer. What else?
