Prosthetic hands are usually designed to be operated by the same muscles that would be used if the person had their natural hand, but a small study suggests that using unrelated muscles instead could ultimately lead to better control.
鈥淭he field needs to change,鈥� says at the University of Pittsburgh in Pennsylvania. 鈥淧eople can learn to do new things remarkably聽well and we can leverage that learning.鈥�
Most prosthetic hands in use today are either rigid or allow just a simple open-and-closing motion with all the fingers moving together.
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More sophisticated devices for commercial use are in development that allow motions such as rotation and separate finger movements. These are usually manipulated using sensors over nerves or muscles in part of the person鈥檚 arm, but the best way to control them is unclear.
Schone鈥檚 team investigated a new approach by asking 40 able-bodied people to undergo training over four days with an advanced prosthetic limb called the i-LIMB Quantum Hand strapped to their wrists, while their corresponding real hands were bound so they couldn鈥檛 move. They learned to move the robot hand in three ways: opening and closing all the fingers and pinching the index finger or the index and middle fingers to the thumb.
In half the group, the electrodes were placed so that usual muscle movements brought about corresponding motions of the bionic hand, known as a biomimetic approach. In the rest, the electrodes were set up so the same bionic hand tasks were achieved by unrelated muscle movements, such as those used to hold up one finger.
Initially, the biomimetic strategy helped people learn to use the robot hand faster, but the non-biomimetic strategy was more efficient when people were later asked to learn two new movements with the hand: making a thumbs-up sign and pinching the little finger to the thumb.
This suggests the non-biomimetic approach gives users more flexibility to learn new tasks, says at the Swiss Federal Institute of Technology in Lausanne. 鈥淚t鈥檚 more complicated at the beginning to grasp, but leaves more freedom to the user,鈥� he says. 鈥淵ou don鈥檛 constrain the person too much.鈥�
There could be a trade-off, however, as people may give up on the robot limb if non-biomimetic control systems take too long to learn, says Micera.
Schone says the findings back up people seemingly finding it easy to learn to use completely novel body parts, such as a prosthetic third thumb controlled by the toes made by report co-author, at University College London.
Nature Human Behaviour
