According to University of Alberta (U of A) research, upper-limb prosthesis users have to look at the object they are interacting with longer than their able-bodied counterparts, which prevents them from planning their next movement. To help dissect the processes behind each hand movement toward improvement of the next generation of prostheses, a U of A research team used motion and eye tracking data to understand how to improve users’ ability to control the devices.
“There are prosthetic devices becoming available that are almost indistinguishable from real limbs, but the real problem is, if you think about how many different ways you can move your hand, each one of those would need a separate channel of information,” said Craig Chapman, PhD, a movement neuroscientist in the Faculty of Kinesiology, Sport, and Recreation at the university who is leading the research. Chapman and his team are interested in the kinds of unconscious movement decisions and the numerous computations necessary to do something as simple as reaching for a doorknob to open a door.
The research team developed a tool called Gaze and Movement Assessment to track body and eye movements among a group of upper-limb prostheses users. The participants were fitted with a head-mounted eye tracker that fits like a pair of glasses, and motion capture markers were placed on the upper limb being tracked, as well as on any other body parts of interest, like the head or torso. Participants were then asked to perform two tasks that mimic what prosthesis users would encounter in the real world: grabbing and moving a small box to three different shelf positions, and moving a cup filled with beads.
“And while they sound like simple tasks, because they were designed with a clinician and occupational therapist, they challenge prosthetic users in unique ways,” said Chapman. “Getting them to do the movement consistently is what allows us to look at averages and determine what part of a particular movement is so difficult.”
Measures of hand movement, angular joint kinematics, and eye gaze were compared with those from a sampling of adults without amputations who performed the same protocol with different technology. The research showed that the prosthetic limb users continued to look at the device and the object, whereas able-bodied individuals look ahead to where they are going to put the object down.
“Their eyes are free to go to the next place and start planning a successful movement,” he said.
Chapman said his studies showed that the participants with amputations often overcompensated to complete the task. For example, users of body-powered prostheses put extra strain on their shoulder and trunk because they have limited degrees of freedom at the wrist.
“They will adapt their body to finish the movement, but maybe they’re doing it in a way that might eventually cause some sort of fatigue injury.”
Editor’s note: This story was adapted from materials provided by U of A.