Embodying an invisible face makes us feel unseen
Recent developments in simulating invisibility allow investigation into the experience of being truly unseen.
11 September 2023
By Emma Young
From Plato to Tolkien, writers have long been fascinated by the idea of becoming invisible. Their ideas about how that might affect a person's feelings and behaviour were, of course, necessarily speculative. Recently, though, psychologists have been working to close the gap between fiction and reality.
Techniques to make people feel as though their bodies have in fact become invisible are allowing us to investigate the ways in which invisibility could affect us psychologically. Previous studies have identified that simulated invisibility reduces anxiety when standing in front of a crowd of strangers, for example, and that it prompts reductions in desired interpersonal space.
Now Mariano D'Angelo at the University of Bologna and Birkbeck, London, and colleagues have developed a technique that makes people feel that their face has become invisible. In a paper in the Journal of Experimental Psychology: General, they report that, as with previous whole-body research, the illusion seemed to succeed in making the participants feel less visible, and so less exposed to other people's attention.
The invisible body illusion technique starts like this: participants wear a head-mounted display that displays video from a camera that is pointing at the floor. When they look down, they see not their own bodies, but empty space. Similarly to the technique for the rubber hand illusion, the experimenter then strokes the participant's body with a paintbrush while synchronously moving another paintbrush in the corresponding positions in the empty space. This tends to make people feel that these touch sensations are happening 'in' the empty space, and so that their body has become invisible.
To target the face instead, the team used green screen technology. They recorded a face being stroked in various places with a paintbrush, then replaced the face with video of the background. This made it look as though an invisible face was being stroked, complete with appropriate pressure applied to the brush's bristles.
In their first experiment, 20 participants watched this video while having their own face stroked in the same places. Sometimes, the timing of the stroking on their own face was synchronous with the stroking in the video. Other times, it was not.
The team found that, as expected from previous work on body-related illusions, the synchronous stroking led participants to agree more strongly with statements that tapped into feelings of ownership of the invisible face — for example, 'It seemed like my face was at the location where I saw the paintbrush moving' and 'It seemed like the touch I felt was caused by the paintbrush I saw moving.' This suggests that the participants did experience an illusion of embodying the invisible face.
In a second experiment, as well as asking the participants about their experiences, the researchers also introduced a knife into the video — at the end of the stroking, the knife suddenly came into view and made contact with the right side of the invisible face, before withdrawing.
If another object is 'adopted' as being part of one's own body, then a threat to that object should trigger a physiological threat response. And indeed, that is what the team found. The participants sweated significantly more in response to the knife after the synchronous stroking than the asynchronous stroking.
Having demonstrated that the invisible face illusion can be induced, the researchers then explored whether the feeling of facial invisibility might affect what's known as the 'cone of gaze'. This refers to the range of deviations in someone else's gaze direction that will all make someone feel that they are being looked at.
Other research has found that various factors can affect the size of this 'cone'. For example, people with social anxiety have a wider cone of gaze. This is thought to relate to heightened perceptions that other people's attention is directed at them.
Using fresh groups of participants, D'Angelo and his colleagues found that the invisible face illusion shrank the cone of gaze, while an illusion in which people were made to feel ownership over another visible face did not. This suggests that the invisible face illusion led participants to feel less observed by other people.
"Enfacing an invisible face may lead participants to share the characteristic of being invisible, that is, the impossibility of being gazed upon, thus reducing the gaze deviations perceived as directed toward the self," the researchers write.
This is the first study to demonstrate an invisible face illusion, and the sample sizes in the experiments were small. More research will be required to explore this new illusion, and its potential effects on social perceptions.
Even so, this preliminary work does shift ideas about what it might be like to have an invisible face from the realm of fiction into fact.
