A robotic arm with a sense of touch has allowed a man who is paralyzed to quickly perform tasks like pouring water from one cup into another.
The robotic arm provides tactile feedback directly to the man's brain as he uses his thoughts to control the device, a team reports Thursday in the journal Science.
Previous versions of the arm required the participant, Nathan Copeland, to guide the arm using vision alone.
"When I only had visual feedback, I could see that the hand had touched the object," Copeland says. "But sometimes I would go to pick it up and it would fall out."
A typical grasping task also took Copeland about 20 seconds to complete. "With sensory feedback he was able to complete it in 10," says Jennifer Collinger, an associate professor in the department of physical medicine and rehabilitation at the University of Pittsburgh.
Tactile information is important for using a robotic arm of limb prosthesis because it's hard to grasp an object you can't feel, Collinger says.
"Even something simple like picking up a cup and trying to maintain the appropriate amount of pressure as you move it to another location, that relies a lot on the tactile feedback from your hand," she says.
So Collinger and a team of researchers have spent years looking for ways to add sensory feedback to a robotic arm and hand.
The team has been working with Copeland, who was paralyzed in an accident as a teenager more than 15 years ago. He has learned to control the motions of the robotic arm using a brain-computer interface.
The team began by placing electrodes in an area of Copeland's brain that processes sensory information. That allowed them to use electrical pulses to simulate a range of sensations.
"It turned out that stimulating in the fingertip-related areas in the brain generated sensations that felt like they were coming from the participant's own hand," Collinger says.
Next, the team figured out how to generate those signals when the robotic arm and hand made contact with something. The final step was to time Copeland as he performed tasks like picking up a block or pouring water, with and without tactile feedback.
The results showed that Copeland could perform some manual tasks roughly as fast as a person using their own hand.
"The sensation would actually change intensity based on how much force the hand was exerting on the object," Copeland says. "So I could also tell if I had a firm grip on it or not."
Copeland says as an added benefit, adding a sense of touch made using the robotic arm feel more natural.
"The control is so intuitive that I'm basically just thinking about things as if I were moving my own arm," he says.
The results have implications beyondrobotic arms, says Jeremy D. Brown, the John C. Malone assistant professor in the mechanical engineering department at Johns Hopkins University.
High-tech prosthetic limbs also work better when they simulate a sense of touch, he says. Some do this by vibrating or providing some other form of haptic feedback – the same approach many smartphones use to help users type on a screen.
The latest prosthetic arms "operate just like our natural limbs do," Brown says. They're able to bend at the elbow, rotate at the wrist, and grasp with fingers.
"But when you give somebody the ability to control these things, until they have the haptics, it's clunky," he says.
And most sensors still have only rudimentary abilities, he says, like detecting resistance or temperature.
When his own hand touches something, Brown says, "I feel the pressure, I feel the slip, I feel whether the object is wet or dry, I can feel the texture of it, I know whether it's rough, whether it's smooth."
Scientists are just beginning to learn how to make artificial hands and fingers that can detect these subtle features of an object. And as prosthetic or robotic limbs provide more sensory feedback, they will become more useful, Brown says.
But he says a sense of touch is about more than just increasing dexterity.
"It's not just the ability to reach into your pocket and grab your keys," he says. "It's also the ability to hold a loved one's hand and feel that emotional connection."
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