Multisensory Illusions in Peripersonal Space Using Tools in Reality and Virtual Reality

Humans can rapidly and accurately tailor their actions in a task when given a tool. Multisensory neurons for proprioception, touch, and vision have been found to change receptor field sizes in non-human primates during tool use. These multisensory neurons are critical in defining body schema along with the borders of peripersonal and extrapersonal space. Studies have shown that humans change the estimation of body part lengths during tool use, and have typically found that arm length estimates increase in response to tool use. This study aimed to replicate the results of previous human tool use studies by administering an arm midpoint estimation task to participants after actively using an 83cm long rod as a tool for five minutes. In addition, the tool and tool use task were recreated in virtual reality, and participants performed the midpoint estimation again after five minutes of practice. Participants then performed one final midpoint estimation task after watching their own actions in virtual reality that they had performed in the earlier virtual reality task. While watching their own actions, participants kept their arms in a neutral position and did not hold the tool. Participants significantly underestimated the distance to the midpoint of their arms after the reality and virtual watching conditions. These results show that the functionality and purpose of a tool may relate to its impact on limb size estimation, body schema, and peripersonal space. Furthermore, these effects still arose in virtual reality, even when participants were only given the visual stimuli of the practice task without the proprioceptive, touch, or motor elements