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See Inside September / October 2011

The Eyes Have It

Eye gaze is critically important to social primates such as humans. Maybe that is why illusions involving eyes are so compelling



Courtesy of ROB JENKINS University of Glasgow

The eyes are the window to the soul. That is why we ask people to look us in the eye and tell us the truth. Or why we get worried when someone gives us the evil eye or has a wandering eye. Our language is full of expressions that refer to where people are looking—particularly if they happen to be looking in our direction.

As social primates, humans are keenly interested in determining the direction of gaze of other humans. It is important for evaluating their intentions and critical for forming bonds and negotiating relationships. Lovers stare for long stretches into each other’s eyes, and infants focus intently on the eyes of their parents. Even very young babies look at simple representations of faces for longer than they look at similar cartoonish faces in which the eyes and other features have been scrambled.

In this article, we investigate a series of illusions that take advantage of the way the brain processes eyes and gaze. It turns out that it is fairly easy to trick us into thinking that someone is looking somewhere else.

GHOSTLY GAZES
Not knowing where a person is looking makes us uneasy. For this reason, it can be awkward to converse with somebody who is wearing dark sunglasses. And it is why someone might wear dark sunglasses to look “mysterious.”

A recently identified visual illusion takes advantage of the unsettling effect of uncertainty in gaze direction. The “ghostly gaze” illusion, created by Rob Jenkins of the University of Glasgow in Scotland, was awarded second prize in the 2008 Best Illusion of the Year Contest, held in Naples, Fla. In this illusion (left and center), twin sisters appear to look at each other when seen from afar. But as you approach them, you realize that the sisters are looking directly at you!

The illusion is a hybrid image that combines two pictures of the same woman. The overlapping photos differ in two important ways: their spatial detail (fine or coarse) and their direction of gaze (sideways or straight ahead). The images that look toward each other contain only coarse features, while the ones that look straight ahead are made up of sharp details. When you approach the pictures, you are able to see all the fine detail, and so the sisters seem to look straight ahead. But when you move away, the gross detail dominates, and the sisters appear to look into each other’s eyes. See an interactive demo at http://illusioncontest.neuralcorrelate.com/2008/ghostly-gaze.

In another example of a hybrid image (right), a ghostly face appears to look to the left when you hold the page at normal reading distance. Step back a few meters, however, and she will look to the right.

CONTEXTUAL CUES
Contextual cues, such as the position of the face and the head, also influence the perceived direction of gaze. In this illusion created by Akiyoshi Kitaoka, a professor of psychology at Ritsumeikan University in Japan, the girl on the left appears to gaze directly at you, while the girl on the right appears to be looking to her left. In reality, the eyes of both girls are identical. This illusion was first described in 1824 by British chemist and natural philosopher William Hyde Wollaston, who also discovered the elements palladium and rhodium.

EINSTEIN’S ALTER EGOS
The ghostly gaze illusion is based on a hybrid-image technique created by Aude Oliva and Philippe G. Schyns of the Massachusetts Institute of Technology. In a shocking example of how perceptual interpretation of hybrid images varies with viewing distance, Albert Einstein, seen from up close, becomes Marilyn Monroe (left) or Harry Potter (right), when seen from a few meters away. For more hybrid images created by the Oliva laboratory, visit the hybrid image gallery at http://cvcl.mit.edu/hybrid_gallery/gallery.html.

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