As artificial intelligence advances, future prosthetic arms may be able to move on their own to assist users with daily tasks.
But for these devices to be truly helpful, people must feel comfortable using them — and ideally experience them as part of their own body.
A new study explores how the movement speed of an autonomous robotic arm affects whether it feels natural or unsettling.
Researchers reported in the journal Scientific Reports that they used virtual reality to simulate a scenario in which a participant’s real arm was replaced by a robotic prosthetic arm.
The goal was to understand how different movement speeds influence a person’s sense of body ownership, control, usefulness, and emotional reactions to the device.
Prosthetic limbs are essential for people who have lost an arm or hand, and most research has focused on improving how users control them using muscle or brain signals.
However, new technologies may allow future prostheses to act independently, using AI to predict what the user needs and move accordingly.
While this could make tasks easier, it also raises a concern: if a limb moves without conscious control, it may feel strange or not truly part of the body.
To study this, scientists created a virtual avatar whose forearm was replaced by a robotic limb. Participants wore virtual reality headsets and performed reaching tasks while the robotic arm moved automatically toward targets.
The researchers adjusted the movement speed across a wide range, from extremely fast to very slow, and asked participants to rate how natural and comfortable the experience felt.
The results showed that speed matters greatly. When the robotic arm moved at a moderate pace similar to natural human movement — taking about one second to reach a target — participants reported the strongest sense that the arm belonged to them. They also felt more in control and rated the device as more usable.
When the arm moved too quickly or too slowly, people felt less connected to it and found it harder to accept as part of their body. Extremely fast movements also caused the greatest discomfort, while moderate speeds created more positive impressions of competence.
The findings suggest that designing future prosthetic limbs is not just about making them faster or more powerful. Matching human-like movement patterns may be key to helping users feel comfortable and confident. The research could also influence the design of other wearable robotic technologies, such as exoskeletons or extra robotic limbs that enhance human abilities.
Scientists note that people can adapt to tools over time, eventually experiencing them as extensions of their bodies. Long-term use of advanced prosthetics might lead to similar adaptation, making even autonomous movements feel natural.
Virtual reality played an important role in the study because it allowed researchers to safely test technologies that do not yet exist in everyday life. By understanding the psychological factors behind acceptance, engineers can design future robotic limbs that feel less like machines and more like part of the person using them.
Ultimately, the research highlights that the success of AI-powered prosthetics will depend not only on technology, but also on how human they feel.
