If using vibrators to shrink your waistline makes you think of spam email, you may be surprised to find out it’s the basis of a fascinating neuroscience experiment published in open-access science journal PLoS Biology.
The study relies on an unusual effect called the Pinocchio illusion, which occurs when a vibrating sensation is applied to the outside muscle on one of the body’s joints. This causes a feeling of the joint closing, when in fact it remains in the same position.
This feeling of movement can conflict with other bodily sensations, and can produce the unusual feeling that body parts are becoming warped or elongated, just like Pinocchio’s nose.
In Ehrsson’s experiment, they applied a vibrating sensation (the blue boxes in the diagram) to the back of each wrist, which gave the false impression that the hands were moving in towards the legs.
While this was happening, Ehrsson and his team brain-scanned the participants to detect active brain areas, and compared conditions where participants were touching vs not touching their legs; and where the vibration was applied to the joint muscles vs another area on the hands.
Crucially, only in the condition when the participant’s hands were touching their legs and the wrist joint muscles were being vibrated, did it feel as if their waste was shrinking to accommodate the illusory movement.
The team found that the strength of the illusion was associated with activity in areas of the left parietal lobe, which are known to be involved in creating the sensation of body shape, also called ‘body image’.
The study suggests that the brain generates body image by making a best guess from the incoming tactile information.
In other words, because the wrist jounts were providing ‘false’ information – indicating that the hands were moving through space occupied by the legs – the brain simply ‘guessed’ that the waist must be smaller to make sense of the discrepancy.
If you want to try this effect at home, a couple of vibrating sex toys are probably your best bet. If you don’t have any, now’s your chance to freak out your local sex shop by asking them to recommend the best dildo for cognitive neuroscience experiments.
Link to study summary.
Link to full text paper.
Link to write-up from nature.com
Link to write-up from BBC News.