A research team led by the University of Tokyo has developed a virtual robotic limb system that can be operated by users’ feet in a virtual environment as extra, or supernumerary, limbs. After a period of training, users reported feeling as if the virtual robotic arms have become part of their own body. Understanding the perceptual changes in participants using this system can aid in designing physical robotic supernumerary limb systems which people can use freely and naturally as parts of their bodies.
By creating this virtual system, scientists aimed to explore the limits of human plasticity – our brain’s ability to alter and adept to both internal and external changes. Brain plasticity is crucial for learning how to use new tools, and sometimes even begin to feel them as extensions of ourselves.
“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 study lead author Ken Arai, a doctoral student at the University of Tokyo.
Participants were asked to wear a head-mounted display that gave them a first-person view of their own arms represented in virtual reality (VR), as well as several additional virtual robotic arms that they could control by moving their toes. When touching objects, such as a virtual ball, tactile devices returned sensations from the virtual robotic arms to the tops and soles of participants’ feet.
After a period of training, participants reported feeling as if the virtual arms became part of their bodies. “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,” explained Arai.
Moreover, the researchers found that participants’ “peripersonal space” – the area around our bodies that we perceive as being our personal space – extended to include the region around the virtual robotic arms too. “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),” said Arai.
In future research, Arai and his team aim to explore the potential for cooperative behavior between participants’ own arms and the virtual ones. By understanding the perceptual changes and cognitive effort needed to operate these arms will help designing real-life robotic systems that people can feel and use like their own body.
The study is published in the journal Nature Scientific Reports.