Your mouth may not be where you think it is. An illusion that tricks people into thinking their teeth are closer to their neck than in reality shows that our bodily perceptions are easily influenced.
Davide Bono and Patrick Haggard at University College London developed the experiment inspired by the rubber hand illusion, a famous illusion in psychology where the participant believes a rubber hand is their own.
In Bono and Haggard’s experiment, the participant wears a blindfold and places their head on a chin-rest. They are then told that Bono will take their right hand and use it to stroke their own teeth.
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Instead, he uses the person’s hand to stroke a model set of human teeth made of plaster placed 8 centimetres below their real teeth. Simultaneously, Bono uses his own hand to stroke the person’s teeth in exactly the same way. The participants are then asked to point to their own teeth.
Eight people took part in the experiment and on average they pointed 1.5 centimetres below their own teeth in the direction of the model teeth. The participants also believed that they were touching their own teeth.
Jaw dropping
The experiment suggests that our perception of our mouth is flexible – an effect called proprioceptive drift. This effect also happens with the rubber hand illusion.
Bono and Haggard found that even if the strokes on the model teeth and the participant’s real teeth were in opposite directions, as long as they started and finished at the same time the illusion still persisted.
They also found that the illusion worked when the model teeth were covered in Velcro. With a different set of model teeth where there were gaps between the teeth, proprioceptive drift didn’t occur, but the participants still believed the model teeth were theirs.
It’s not clear why this should be the case, but Bono says we may have some higher-level conception of what our teeth should be like, but one that can still be easily manipulated.
The experiment hints that we learn where our mouth is by trial and error rather than by something innate. It contributes to our understanding about how flexible our sense of body positions are, says Esther Kuehn at University Hospital Magedeburg in Germany.
Journal reference:ÌýEuropean Journal of Neuroscience,ÌýDOI: https://onlinelibrary.wiley.com/doi/pdf/10.1111/ejn.14508
