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Two arms good, three arms better

Published: 04th September, 2018 at 08:55
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Researchers teach volunteers to control a robotic third arm through a brain-machine interface.

Because two arms just aren’t enough, researchers from the Hiroshi Ishiguro Laboratory in Kyoto, Japan, have taught volunteers to control a robotic third arm through a brain-machine interface.


Participants in the experiment were challenged to balance a ball on a board using their hands, and pick up a bottle using a robotic third arm. Fifteen subjects took part, and eight of them managed the task successfully.

For now, the robot arm is quite basic: it can only open and close its hand. The brain-machine interface is similarly rudimentary: it’s a cap fitted with electrodes that measures the brain’s electrical signals. Before the test, participants imagined opening and closing the robotic hand, and those brain signals were recorded and turned into an instruction for the robotic arm.

Uses for extra limbs have already established. An MIT concept device developed in 2012 saw users wear extra limbs like a backpack. They were used to hold tools and parts in manufacturing, and to support the user in sitting positions. But while it’s a long way off being practical, this is the first time that an extra limb has been controlled straight from the brain. In the past, robotic prosthetics have been controlled using signals from muscles or external joysticks, and they’ve usually been intended as replacement limbs, not supplementary ones.

The researchers also noted that success in the task depended heavily on the participants’ ability to multitask. They suggested that operating the extra limb through the brain-machine interface might help users improve their multitasking abilities.

This is an extract from issue 326 of BBC Focus magazine.

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