Robotic Prosthetics: How Body Image Affects Learning to Walk | Futurity

The Evolving Perception of Movement with Robotic Prosthetics

Learning to walk, dance, or play a sport relies heavily on our internal understanding of how our bodies move. However, a new study published in PNAS Nexus reveals that this process differs significantly for individuals learning to use robotic prosthetic devices. The research, conducted by scientists at North Carolina State University and the University of North Carolina at Chapel Hill, sheds light on how people adapt to and perceive movement when a limb is replaced by a robotic one.

“When people first start walking with a prosthetic leg, they think their bodies are moving more awkwardly than they really are,” explains Helen Huang, a professor of biomedical engineering and the corresponding author of the study. This initial perception of awkwardness is a common experience, but the study’s findings reveal a surprising shift as users gain experience.

As performance improves with practice, individuals don’t necessarily develop a more accurate assessment of their movement. Instead, their perception becomes inaccurate in a different way. They begin to *underestimate* the degree of awkwardness, often feeling more fluid and natural than their actual gait suggests. This phenomenon raises important questions about how the brain integrates a prosthetic limb into its body image and how this impacts the learning process.

Understanding Body Image and Movement

The study builds upon the concept of “body image” – our internal understanding of our body’s structure and how it moves. This internal map is crucial for learning new physical skills. Typically, when learning something like dancing, our mental image of our movements doesn’t perfectly align with reality. However, with practice, this mental image refines itself, leading to improved performance. The researchers were interested in understanding whether individuals using robotic prosthetics incorporate the device into this existing body image and how that process unfolds.

“We wanted to learn more about how and whether people who are using robotic prosthetics incorporate that prosthetic device into their body image,” Huang says. “Does that change as people become more familiar with using these devices? Is there any relationship between incorporating these devices into one’s body image and their performance using these devices?”

The Study Design

To investigate these questions, the researchers recruited nine able-bodied participants. Over four days, participants walked on a treadmill using a robotic prosthetic attached to a knee bent at a right angle. They were instructed to walk as quickly as possible without using the handrails. After each practice session, participants were presented with computer animations depicting various walking gaits and asked to select the animation that most closely resembled their own performance with the prosthetic.

The results revealed a consistent pattern. Initially, participants perceived their gait as more unstable and jerky than it actually was. By the end of the four-day study, their perception had shifted – they felt their gait was smoother and more natural, even though objective measurements indicated it still wasn’t perfectly fluid. Importantly, while performance improved significantly over the study period, participants remained inaccurate in their self-assessment, albeit with increased confidence.

Focus on Torso Position, Limited Feedback on the Device

The researchers also discovered that participants tended to focus on the position of their torso when evaluating their gait. They placed less emphasis on the behavior of the prosthetic device itself. This finding suggests that a lack of direct feedback about the prosthetic’s movement may contribute to the inaccurate self-perception.

“One reason for this is likely because they are receiving very little direct feedback about the behavior of the device—they can’t see themselves moving,” Huang explains. This highlights a potential avenue for improving prosthetic training: providing users with visual or other sensory feedback about the device’s operation could help them calibrate their body image and refine their gait.

Addressing Overconfidence and Improving Training

The study also points to the importance of addressing overconfidence in movement skills. If individuals believe they are performing well when they are not, they may be less motivated to continue practicing and improving. Providing more accurate assessments of movement could encourage continued effort and lead to better outcomes.

“If you already think you’re doing great, you’re less likely to put in the work necessary to get better—even if there is significant room for improvement,” Huang says. “We think it would be valuable to find a way to give people a more accurate assessment of how their body is really moving.”

This research, supported by the National Institutes of Health and the National Science Foundation, represents a crucial step towards optimizing prosthetic training and improving the lives of individuals who rely on these devices. By understanding how the brain adapts to and perceives movement with a robotic limb, researchers can develop more effective strategies to help users achieve greater mobility and a more natural sense of embodiment. The findings underscore the complex interplay between perception, performance, and the integration of technology into the human body.