Researchers at Ruhr University Bochum, Germany, have used virtual reality (VR) to gain new insights into human perception. It just goes to show that VR is not simply a gaming and leisure technology; it also has scientific and medical applications.
The team used virtual reality scenarios in which subjects touched their own bodies with a virtual object. To the researchers’ surprise, this resulted in a tingling sensation where the avatarized body was touched.
This effect occurred even though there was no real physical contact between the virtual object and the body. The scientists – led by Dr. Artur Pilacinski and Professor Christian Klaes from the Department of Neurotechnology – describe this phenomenon as a phantom touch illusion.
“People in virtual reality sometimes have the feeling that they are touching things, although they are actually only encountering virtual objects. We show that the phantom touch illusion is described by most subjects as a tingling or prickling, electrifying sensation or as if the wind was passing through their hand,”
said first author Artur Pilacinski from the Knappschaftskrankenhaus Bochum Langendreer, University Clinic of Ruhr University Bochum, explaining the origin of the research question.
Complex Mix of Body Sensations
The neuroscientists wanted to know what was causing this event and what mechanisms in the brain and body were involved. The phantom touch illusion was also noticed when the subjects touched regions of their body that were not visible in virtual reality.
“This suggests that human perception and body sensation are not only based on vision, but on a complex combination of many sensory perceptions and the internal representation of our body,”
added second author Marita Metzler.
This study involved 36 volunteers wearing VR glasses. First, they got used to the VR environment by moving around and touching virtual objects. Then they were given the task of touching their hand in the virtual environment with a virtual stick.
That Phantom Touch Illusion
Participants were asked if they felt anything. If not, they were allowed to continue touching, and the question was addressed again later. If they felt feelings, they were asked to describe them and score their severity on several hand regions.
This process was repeated for both hands. There was a consistent reporting of the sensation as “tingling” by a majority of participants.
In a control experiment, it was determined whether equivalent sensations could be perceived without visual contact with virtual objects only due to the demands of the experimental environment. Instead of virtual items, a tiny laser pointer was employed to touch the hand in this case.
This control experiment did not result in phantom touch, suggesting that phantom touch illusion was unique to virtual touch.
New Research Possibilities
The discovery of the phantom touch illusion opens up new possibilities for further research into human perception and could also be applied in the fields of virtual reality and medicine.
“It could even help to deepen the understanding of neurological diseases and disorders that affect the perception of one’s own body,”
said Christian Klaes, member of the Research Department of Neuroscience at Ruhr University.
The Bochum team intends to continue their investigation into the phantom touch illusion and its underlying processes. As a result, a relationship with the University of Sussex has begun.
“It is important to first distinguish between the actual sensations of phantom touch and other cognitive processes that may be involved in reporting such embodied sensations, such as suggestion, or experimental situation demands,”
said Artur Pilacinski. In collaboration with other partners, the team also hopes to investigate further and comprehend the neural basis of the phantom touch illusion.
We report the presence of a tingling sensation perceived during self-touch without physical stimulation. We used immersive virtual reality scenarios in which subjects touched their body using a virtual object. This touch resulted in a tingling sensation corresponding to the location touched on the virtual body. We called it “phantom touch illusion” (PTI). Interestingly, the illusion was also reported when subjects touched invisible (inferred) parts of their limb. We reason that this PTI results from tactile gating process during self-touch if there is no tactile input to supress. The reported PTI when touching invisible body parts indicates that tactile gating is not exclusively based on vision, but rather on multi-sensory, top-down input involving body schema. This supplementary finding shows that representations of one’s own body are defined top-down, beyond the available sensory information.
- Pilacinski, A., Metzler, M. & Klaes, C. Phantom touch illusion, an unexpected phenomenological effect of tactile gating in the absence of tactile stimulation. Sci Rep 13, 15453 (2023). doi: 10.1038/s41598-023-42683-0