Skip to main content

All Deceptions Great and Small

Does size matter? To your brain, it doesn't


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


Size matters not. Look at me. Judge me by my size, do you? —Yoda, Jedi master

As both the midget in the country of Brobdingnag and the giant on the island of Lilliput, Lemuel Gulliver—the protagonist of Jonathan Swift's Gulliver's Travels—experienced firsthand that size is relative. As we cast a neuroscientific light on this classic book, it seems clear to us that Swift, a satirist, essayist and poet, knew a few things about the mind, too. Absolute size is meaningless to our brain: we gauge size by context. The same medium-sized circle will appear smaller when surrounded by large circles and bigger when surrounded by tiny ones, a phenomenon discovered by German psychologist Hermann Ebbinghaus. Social and psychological context also causes us to misperceive size. Recent research shows that spiders appear larger to people who suffer from arachnophobia than to those who are unafraid of bugs and that men holding weapons seem taller and stronger than men who are holding tools. In this article, we present a collection of illusions that will expand your horizons and shrink your confidence in what is real. Try them out for size!

(Further Reading)

Sleights of Mind: What the Neuroscience of Magic Reveals about Our Everyday Deceptions. Stephen L. Macknik and Susana Martinez-Conde, with Sandra Blakeslee. Henry Holt, 2010.

Applying the Helmholtz Illusion to Fashion: Horizontal Stripes Won't Make You Look Fatter. Peter Thompson and Kyriaki Mikellidou in i-Perception, Vol. 2, No. 1, pages 69–76; 2011.

It Was as Big as My Head, I Swear!: Biased Spider Size Estimation in Spider Phobia. M. W. Vasey, M. R. Vilensky, J. H. Heath, C. N. Harbaugh, A. G. Buffington and R. H. Fazio in Journal of Anxiety Disorders, Vol. 26, No. 1, pages 20–24; January 2012.

Weapons Make the Man (Larger): Formidability Is Represented as Size and Strength in Humans. D.M.T. Fessler, C. Holbrook and J. K. Snyder in PLOS ONE, Vol. 7, No. 4, Article e32751; 2012.

Susana Martinez-Conde is a professor of ophthalmology, neurology, and physiology and pharmacology at SUNY Downstate Health Sciences University in Brooklyn, N.Y. She is author of the Prisma Prize–winning Sleights of Mind, along with Stephen Macknik and Sandra Blakeslee, and of Champions of Illusion, along with Stephen Macknik.

More by Susana Martinez-Conde

Stephen L. Macknik is a professor of opthalmology, neurology, and physiology and pharmacology at SUNY Downstate Medical Center in Brooklyn, N.Y. Along with Susana Martinez-Conde and Sandra Blakeslee, he is author of the Prisma Prize-winning Sleights of Mind. Their forthcoming book, Champions of Illusion, will be published by Scientific American/Farrar, Straus and Giroux.

More by Stephen L. Macknik
SA Special Editions Vol 22 Issue 3sThis article was originally published with the title “All Deceptions Great and Small” in SA Special Editions Vol. 22 No. 3s (), p. 14
doi:10.1038/scientificamericanillusions0913-14