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Researchers at the University of Tokyo have built a system they call PossessedHand that electrically stimulates ­muscles in the forearm at strategic moments to nudge beginners as they play a traditional Japanese instrument called the koto. One of the researchers, Emi Tamaki, says that people who used the technology were much better at playing the proper rhythm and made fewer mistakes. The prototype system is rudimentary and clunky, but its creators believe it could point the way toward machines that help ­people acquire other skills quickly and easily.

A. Hand
The device can stimulate seven different forearm muscles that control 16 joints in the hand, encouraging them to move in certain ways and at certain times. ­However, the stimuli aren’t strong enough to make a hand grasp objects or play an instrument on its own.

B. Timing Control
For PossessedHand to guide a novice player, it has to deliver stimulation at the right intervals. Because the time it takes for the electrical stimuli to travel to the muscles varies somewhat by individual, the system includes a control, resembling a volume dial, that allows the wearer to adjust the timing of the jolts. On average, subjects need the stimulation to be activated about 0.34 seconds ahead of when they would play a sound.

C. Microcontroller and Switching Board
Users can customize the technology through software that runs on an ordinary computer. An Arduino microcontroller and switching board connected to the PC by a USB cable translate commands from the software to the electrode belts.

D. Electrode Pads and Belts
Fourteen electrode pads stud each of two belts and provide the stimulation that induces muscles to move. A user of PossessedHand will get jolts from only about seven of the electrodes, but the researchers put many more on the device in order to make it easier to adjust the system to individual users’ forearms. The intensity of stimulation can also be ­varied. Lighter stimulation is intended to affect muscles more toward the surface of the arm, while stronger stimulation affects deeper muscle tissue. 

E. Battery and Capacitor
These provide the electrical charges used to stimulate muscles. For safety reasons, the system allows only a limited amount of charge to build up in the capacitor before it is passed on to the wearer.


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