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ATTENTION!
People with mental disorders and nervous do not look these pictures!

LEVIANT ILLUSION - ENIGMA
The French artist Isia Leviant placed coloured circular “avenues” around arrays of radial lines. He noticed that the avenues appeared to contain “blobs” that sometimes move clockwise, sometimes counter-clockwise. He called the figure “Enigma”. It gives rise to what is now sometimes called the “traffic illusion”. He originally called it the L (for live) effect.

ENIGMA
Aysiya Leviant "The Enigma", 1984

LEVIANT ILLUSION - if you look at the picture center, after some time circles start flashing and then rotate
It is also possible to observe the rotation of the radial lines.

An Enigma solved


Look at the center of the left picture. Do you see flicker and spin?
Now move the eye right in the center of the right picture, then again - in the left center, etc ...
So, how is it?
 
ATTENTION! All pictures presented here are absolutely static. Anyone noticed the movement is an illusion.
 
 
 

An Enigma solved
Scientists determined why we see illusory flowing rings in Enigma

f you will humor us, please stare at the center dot in the picture to the left. Does it appear that the rings are moving? Now, do it a second time, but consciously fixate your eyes very strictly at the center. Finally, stare at the center a third time while only loosely fixating your eyes. Does the apparent flow of the rings change relative to how steady your eyes remained?

Ever since French artist Isia Leviant drew Enigma in 1981, scientists and artists have wondered why we perceived flowing movements to the concentric rings. Scientists have collected evidence to support or discount a few hypotheses. For example, brain imaging of people looking at the picture showed activity in the area of the brain that is responsible for identifying movement. This led scientists to propose that brain processes caused the illusion of movement in Engima.

Another hypothesis pointed to the regular, rapid movements of the eye (called microsaccade), but this appeared to be ruled out in a different study. In that experiment, participants wore contact lenses attached with a version of the illusion. Scientists believed that it ensured the picture would always stay stationary relative to the eye. Since the volunteers still saw the illusion, it suggested that only the brain was responsible.

A team led by Susana Martinez-Conde from the Barrow Neurological Institute in Arizona found flaws in the previous work. For instance, contact lenses do not remain absolutely still on the eye; they can slip and not keep up with its rapid movements. Martinez-Conde’s research group conducted their own experiment to test if microsaccades produced the appearance of motion.

They asked three subjects to look at a simplified version of Enigma and monitored their eye movements at the rate of 500 times per second using fast video-based system. Whenever the participants thought the perceived motions were slowing down or stopped, they had to press a button. They then released the button when the speed picked up again. By correlating the button pushing and the eye measurements while accounting for the reaction times of the participants, the researchers found that the illusory motions were slowest or stopped when microsaccades were minimal. Fast microsaccades lead to greater perceived movements.

Thus, microsaccades seem responsible for the false impression, but this doesn’t rule out other contributing factors. For instance, Martinez-Conde named the accommodation fluctuation of our eyes as another possible trigger. Accommodation is the change in the shape of our lens when we shift our attention from a distant point to a close one, but it also happens when we’re holding our gaze. Experiments that address accommodation fluctuations will be necessary to determine its role in the illusion of Enigma.

Proceedings of the National Academy of Sciences, 2008.

 
 
 
  REFERENCES::
• Zeki S, Watson JD, Frackowiak RS (1993) Going beyond the information given: the relation of illusory visual motion to brain activity.
• Leviant I (1996) Does ‘brain-power’ make Enigma spin? Proc R Soc London B 263:997–1001
• Barch D, Kumar T, & Glaser DA (2003) Modeling the illusory motion of Enigma with an excitable neuronal array [Abstract]. Journal of Vision, 3:72a
 
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