This Bizarre Illusion Makes You Misplace Your Own Mouth

The volunteers believed that false teeth were their own. Pla2na/Shutterstock

Using a blindfold, a set of false teeth, and some good old-fashioned trickery, scientists at University College London (UCL) managed to persuade eight people that their mouths weren’t where they thought they were.

The so-called dental model illusion, described in the European Journal of Neuroscience, was conceived by UCL’s Davide Bono and Patrick Haggard as a way of determining whether our perception of our mouth’s position is a natural instinct or something we learn.

The duo blindfolded their volunteers and had them place their chins on a chin rest. Directly below was a set of false teeth, positioned 8 centimeters (3 inches) beneath the participants’ real teeth. Each volunteer was told that Bono would take their right hand and stroke their teeth with it. In reality, Bono stroked their teeth with his own hand while the participant’s fingers touched the dummy teeth.  

Then, when asked to point to their own teeth, the participants missed the mark, pointing to a spot 1.5 centimeters (0.6 inches) below their own gnashers on average. What’s more, the volunteers genuinely felt like they were touching their own teeth. 

The same phenomenon occurred with Velcro-covered teeth and when Bono stroked the false teeth and participant’s teeth in opposite directions. The researchers also tested their illusion using fake teeth that had gaps in it. In this scenario, the volunteers didn’t misjudge the position of their mouths but did still believe that the gapped teeth were their own.

So what does all this tell us? In addition to being totally bizarre, the results of the experiment suggest that our perception of where our mouth is is learned through experience, rather than being entirely innate.

"Based on the results we observed in this study, I would say that the awareness of our mouth in space is primarily learnt through experience," Bono told IFLScience. "If we had some even minor innate knowledge on where in space our mouth should be, this information would be clashing with the sensory information received during the dental model illusion."

In their paper, Bono and Haggard note that “infants, and perhaps foetuses, may learn the position of their own mouth, and build a hand‐to‐mouth body model, by trial‐and‐error.” 

The researchers also note that their findings could potentially help to treat people suffering from certain medical conditions. Some diseases, such as Alzheimer’s, can interrupt our ability to feed ourselves properly, as patients often struggle to bring their hand to their mouth. Knowing more about how we perceive the location of the mouth could help scientists to develop new treatments and improve these patients’ quality of life.

The dental model illusion is based on the well-known rubber hand illusion. Here, the participant is made to believe that a dummy hand is their own as the researcher strokes their hand and the pretend hand at the same time. You can check out this weird illusion in the video below.

[H/T: New Scientist

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