Researchers have created a virtual robotic limb system that can be operated by users’ feet as extra, or supernumerary, limbs in a virtual environment. Users reported that after training, the virtual robotic arms felt like they were a part of their own body. This study focused on the participants’ perceptual changes, which can help in the design of real physical robotic supernumerary limb systems that people can use naturally and freely, just like our own bodies.
Researchers at the University of Tokyo, Keio University, and Toyohashi University of Technology in Japan have created a virtual robotic limb system that can be operated by users’ feet in a virtual environment as extra, or supernumerary, limbs. Following training, users reported that the virtual robotic arms had become a part of their own body. This study focused on the participants’ perceptual changes, which can help to design real physical robotic supernumerary limb systems that people can use naturally and freely, just like our own bodies.
What would you do if you had an extra arm, or if you could have four extra arms like Spider-nemesis Man’s Doctor Octopus? Research into extra, or supernumerary, robotic limbs looks at how we might adapt, mentally and physically, to having additional limbs added to our bodies.
We investigated whether virtual robotic arms, as supernumerary limbs, could be perceived as part of one’s own body, and whether perceptual changes would occur regarding the proximal space around the robotic arm.
Ken Arai
Doctoral student Ken Arai from the Research Center for Advanced Science and Technology (RCAST) at the University of Tokyo became interested in this research as a way to explore the limits of human “plasticity” – in other words, our brain’s ability to alter and adapt to external and internal changes. One example of plasticity is the way that we can learn to use new tools and sometimes even come to see them as extensions of ourselves, referred to as “tool embodiment,” whether it’s an artist’s paintbrush or hairdresser’s scissors.
To explore these concepts in action, teams at the University of Tokyo, Keio University, and Toyohashi University of Technology in Japan collaborated to create a virtual robotic limb system. They then asked participants to perform tasks in virtual reality (VR) using the virtual limbs.
“We investigated whether virtual robotic arms, as supernumerary limbs, could be perceived as part of one’s own body, and whether perceptual changes would occur regarding the proximal space around the robotic arm,” said Arai.
Participants wore a head-mounted display, which provided them with a first-person view of their own virtual robotic arms as well as the additional virtual robotic arms. They were then required to complete tasks using only their virtual robotic arms, which they controlled by moving their toes. When they touched an object, such as a virtual ball, tactile devices returned sensations from the virtual robotic arms to the tops and soles of their feet.
After learning how to use the virtual system, the participants reported that the virtual robotic arms had become their own extra arms, rather than just extensions of their real arms or feet. “The scores of subjective evaluation statistically became significantly higher for ‘sense of body ownership,’ ‘sense of agency’ and ‘sense of self-location,’ which are important measures of embodiment, where the supernumerary robotic limb is able to become part of the body,” said Arai.
The team also discovered that the participant’s “peripersonal space” (the area around our bodies that we perceive as our personal space) extended to include the area around the virtual robotic arms. “We succeeded in capturing the positive association between the perceptual change in visuo-tactile integration around the supernumerary robotic limbs (peripersonal space) and the score change of subjective evaluation of feeling the number of one’s arms increased (supernumerary limb sensation,” Arai explained.
The team then intends to investigate the possibility of cooperative behavior between virtual reality participants’ own arms and virtual robotic arms. “From the standpoint of cognitive neuroscience, investigating the mechanisms and dynamics of the supernumerary limb sensation reported here will be important in exploring human plasticity limits and the design of supernumerary robotic limb systems,” said Arai. The hope is that understanding the perceptual changes and cognitive effort required to operate a supernumerary robotic limb system in VR will help in the future design of real-life systems that people can use naturally, just like their own body.
