Anticipating the Future to ‘See’ the Present
staring at a pattern meant to evoke an optical illusion is usually an act of idle curiosity, akin to palm reading or astrology. The dot disappears, or it doesn’t. The silhouette of the dancer spins clockwise or counterclockwise. The three-dimensional face materializes or not, and the explanation always seems to have something to do with the eye or creativity or even personality.
That’s the usual cue to nod and feign renewed absorption in the pattern.
In fact, scientists have investigated such illusions for hundreds of years, looking for clues to how the brain constructs a seamless whole from the bouncing kaleidoscope of light coming through the eyes. Brain researchers today call the illusions perceptual, not optical, because the entire visual system is involved, and their theories about what is occurring can sound as exotic as anyone’s.
In the current issue of the journal Cognitive Science, researchers at the California Institute of Technology and the University of Sussex argue that the brain’s adaptive ability to see into the near future creates many common illusions.
“It takes time for the brain to process visual information, so it has to anticipate the future to perceive the present,” said Mark Changizi, the lead author of the paper, who is now at Rensselaer Polytechnic Institute. “One common functional mechanism can explain many of these seemingly unrelated illusions.” His co-authors were Andrew Hsieh, Romi Nijhawan, Ryota Kanai and Shinsuke Shimojo.
One fundamental debate in visual research is whether the brain uses a bag of ad hoc tricks to build a streaming model of the world, or a general principle, like filling in disjointed images based on inference from new evidence and past experience. The answer may be both. But perceptual illusions provide a keyhole to glimpse the system.
When shown two images in quick succession, one of a dot on the left of a screen and one with the dot on the right, the brain sees motion from left to right, even though there was none. The visual system has apparently constructed the scenario after it has been perceived, reconciling the jagged images by imputing motion.