In a new study published in Scientific Reports, researchers have uncovered a phenomenon known as the “phantom touch illusion,” where individuals experience tactile sensations without actual physical contact in a virtual reality (VR) setting. This intriguing discovery raises questions about how the brain processes sensory information.
Previous research has shown that our nervous system can differentiate between self-generated touch and touch from external sources, a process often described as tactile gating. This ability helps us understand our interactions with the world around us.
When you perform an action that results in self-touch, your brain anticipates this contact. It knows that the sensation is a result of your own movement. Because of this anticipation, the brain ‘turns down the volume’ on the sensory response. Essentially, it partially “cancels” or gates out the sensation because it’s expected and self-generated. This is why you can’t effectively tickle yourself ā your brain knows the touch is coming and reduces the response.
However, the introduction of virtual reality has added a new layer to this understanding. VR users often report feeling sensations that aren’t physically there, especially in social or interactive virtual environments. This led researchers to wonder: could our brains be tricked into feeling touch in a completely virtual setting?
“In virtual reality, people sometimes report feeling slight touch even if there is no actual person or thing touching them. We followed up on casual chats we had about how people sometimes feel things in VR when touching objects. I got interested in whether this has ever been described and what neural/cognitive processes may be behind it,” said study author Art Pilacinski, a postdoctoral researcher in the Klaes Lab at Ruhr-University Bochum.
To explore this, the researchers conducted an experiment with 36 volunteers, aged between 21 and 42 years. These participants, who had little to no prior experience with virtual reality, were immersed in a virtual environment using head-mounted displays (the Oculus Quest 2).
Initially, participants familiarized themselves with the VR setting by interacting with various virtual objects. The main task involved using a virtual stick to touch their own virtual hand. Observers carefully monitored the participants’ reactions and feedback. Participants were asked whether they felt anything when their virtual hand was touched. If they reported a sensation, they were further asked to describe it and rate its intensity on different parts of the hand and forearm.
Most participants (89%) reported a tactile sensation during the experiment. They described this sensation as a tingling, static, prickling, electric feeling, or akin to wind passing through the hand. This sensation, consistent with the position of the virtual stick, was what researchers called “phantom touch illusion.”
An intriguing aspect of the study was that participants also reported feeling the phantom touch illusion on parts of their body that were not visible in the virtual environment, specifically their forearms. This observation is crucial because it suggests that the illusion is not solely dependent on visual cues.
The ability of participants to feel sensations on non-visible body parts indicates a more complex interaction between the brain’s perception of the body and sensory inputs. This finding opens up questions about how the brain integrates different types of sensory information, such as proprioception (the sense of body position and movement) and visual cues, to create a coherent experience of touch.
“We took a phenomenon anecdotally reported by virtual reality users to investigate a physiological process of self-touch cancellation,” Pilacinski told PsyPost. “We see a consistent reporting of this phantom sensation as tingling. But not just that – we also showed that participants felt the phantom touch in the parts of their arm that were invisible to them. This hints us that mapping touch on the body surface is not just based on vision or touch signals itself but rather uses some higher-order body schema mapping.”
To determine whether the phantom touch illusion was unique to the virtual reality setting, a control experiment was conducted. In this experiment, participants used a small laser pointer, projecting a red light onto their skin, instead of interacting with virtual objects. This setup tested whether similar sensations could be induced without the immersive visual cues provided by virtual reality.
The results were significant: far fewer participants (44%) reported any sensation in this control setup compared to the virtual reality scenario. This disparity indicates that the phantom touch illusion is indeed specific to the immersive and visually rich environment of virtual reality, and not merely a result of suggestion or the experimental setup itself.
However, there are some limitations to this study. For one, the sensation wasn’t uniformly experienced by all participants, with four individuals not reporting any phantom touch. This variability suggests that individual differences, such as attention or cognitive processes, might play a role in the experience of phantom touch.
Another point to consider is the reliability of self-reported sensations. The study relied on participants’ subjective descriptions and ratings of the phantom touch, which might not accurately reflect the intensity or nature of the sensation.
Looking ahead, researchers are interested in further exploring the neural mechanisms behind this phenomenon. Understanding how our brain integrates sensory information in a virtual environment could have significant implications for VR technology, both in terms of enhancing user experience and potential therapeutic applications.
“First off we want to distinguish between real sensation of phantom touch and other cognitive processes potentially involved such as suggestion,” Pilacinski said. “For this, we launched a collaborative project investigating cognitive factors in virtual reality embodiment. We will further pursue the investigation of neural basis of the illusion and touch prediction processes.”
“We will also follow up on the concept that touch cancellation may be not depending on vision. For this, we will use neural measures our experimental paradigm is suited for. That means, we will work both on embodiment and touch in virtual reality but also on the neural and cognitive processes that enable such embodiment.”
“We think phantom touch illusion is a great start to study a variety of phenomena such as embodiment in virtual spaces, body schema up to basic research in touch physiology,” Pilacinski added.
The study, “Phantom touch illusion, an unexpected phenomenological effect of tactile gating in the absence of tactile stimulation“, was authored by Artur Pilacinski, Marita Metzler, and Christian Klaes.
