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It's all in the eyes: Isia Leviant's 'Enigma' creates an illusion of motion. Credit: Isia Leviant NEW YORK: Tiny eye movements may be responsible for the optical illusion of a famous artwork. The discovery hints at how we are fooled by other illusions too. The painting, called 'Enigma', is a visual illusion created by artist Isia Leviant in 1981. It consists of concentric circles and radiating black and white lines. When looking at Enigma (see image), most people see what appears to be a flowing movement around the circles. Conflicting theories This kind of optical illusion had been of interest to neuroscientists for many years. Conflicting theories regarding the explanation go back at least two centuries, with experts disputing whether the explanation lies in the eyes or the brain. Now, researchers at the Barrow Neurological Institute in Arizona, U.S., say they've settled the controversy: tiny eye movements called 'microsaccades', which occur one to two times per second when the eye's gaze is fixated, produce at least part of the illusion. This is "first time that a direct correlation was drawn between Enigma and any physiological precursor," said Susana Martinez-Conde, lead researcher behind the study. Her team's results are published in the U.S. journal the Proceedings of the National Academy of Sciences. Previous work by the researchers revealed that the illusion of motion speeds up when the eyes are loosely fixated on the center of Enigma, and slows down or even stops when precisely fixated on the center (try it by looking at the image on the right). For the new study, Martinez-Conde's team showed test subjects simplified versions of Enigma, and asked them to fixate their gaze while reporting their perception of the illusion. Subjects recorded whether the perceived motion was decreasing or speeding up by pressing and releasing a button. "Milestone" study This time the test subjects were simultaneously recorded with high-speed video cameras, which measured their eye movements. The results revealed a correlation between eye flicker and the perceived motion: as eye flicker increased, so did the perceived motion, and when eye flicker decreased, the perceived motion also decreased or stopped. Simone Gori, a psychologist at the University of Trieste in Italy, whose work involves the Enigma illusion, told Cosmos Online that the new research was "a milestone" which "makes the debate [over the illusion] lively and challenging again." Gori added that while flickering eye movements may not explain the entire phenomenon, the study proves that they are necessary to see the illusion. Martinez-Conde said that she would be surprised if this was an isolated case, and that it's likely that flickering eyes could be part of the explanation for illusory motion in many other paintings too. Her future research will focus on the precise brain mechanism that links eye movements to the perception of an illusion. Readers' comments
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eye flicker
If the image is shown very briefly, do people still see the illusion of movement?
Yes. Try it yourself.
Yes. Try it yourself.
Different illusion, but the words never change
Reading this article has revealed nothing in addition to what has already been postulated from research into many of the motion illusions. Eye flickering has inspired many of major theoretical frameworks for such illusions. Do we need to develop new versions of the same illusion to rekindle interest in studying the neuroscience of such illusions?
Trevor Phelps
reply to Trevor Phelps
What you say is wrong, Enigma has peculiar characteristics, read the letterature on that and after, maybe, you will be able to comment this paper.
No, he's not wrong.
There's nothing "peculiar" in this illusion that isn't in plenty of others.
Let's say that all cars have four wheels and an engine. Basically, by saying he's wrong, you're saying that a yellow car deserves special study because it's a different color than most other cars and disregarding the fact that it also has four wheels and an engine.
Read enough of the literature to get a good grasp of what we already know before you start telling others to read about one specific case. After that, maybe, just maybe, you'll be competent enough to comment on others' comments.
Since micro saccadic
Since micro saccadic movements are a normal activity of a healthy eye, why do some people with healthy eyes not perceive the illusion?
Perhaps because saccades are
Perhaps because saccades are neither a necessary nor a sufficient condition to consider an eye healthy.
Try looking at it with one eye closed
Eye flicker? Maybe it's something a little more simple than that. Why is it if you look at the picture with only one eye, the illusion doesn't flow? Maybe the slight offset each eye has from the other and the brain's attempt to combine what both eyes are seeing into one image is what really causes the optical illusion. That and the fact that depth perception requires both eyes. Ya think?
If saccades did not exist,
If saccades did not exist, it's quite possible that this illusion would not happen. That the illusion exists at all is actually a bit of supporting evidence in favor of it being due to saccades and/or microsaccades.
Saccades are not something new that this research is proposing. They've been known about since the 19th century. What is relatively new is the idea that they're the reason for this illusion.