If you’re a bit lax with your post-holiday brushing, this little-known illusion may give you the incentive you need to keep those candy canes in check, or at least brush and floss afterwards. Vision scientist Robert O’Shea and his colleagues published a recent study in PLoS One showing that dentists can fall prey to a visual illusion of size and make larger holes in teeth than needed.
The illusion fooling the dentists is a variant of a classical perceptual phenomenon known as the Delboeuf illusion, named after its creator, the Belgian natural philosopher, experimentalist, mathematician and hypnotist Joseph Remi Leopold Delboeuf.
The scientists supplied 8 specialist dentists and endodontists, who served as experimental subjects, with a large pool of extracted teeth. The teeth contained holes, and the task of the dentists was to cut cavities in preparation for filling. Unknown to the dentists, each tooth presented a more or less powerful version of the Delboeuf illusion, making the holes appear smaller than their actual size. The results showed that the smaller the holes looked, the larger the cavities that the dentists made for later filling. The researchers recommend that dentists and other health practitioners receive training in “illusion awareness” (my words, not theirs), so that they may counteract these and related perceptual effects.
The views expressed are those of the author(s) and are not necessarily those of Scientific American.
ABOUT THE AUTHOR(S)
Susana Martinez-Conde is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. She is author of the Prisma Prize-winning Sleights of Mind, along with Stephen L. Macknik and Sandra Blakeslee. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux.