STARE at this picture long enough and you will see trickling streams flowing in the concentric circles. That鈥檚 because your eyes just can鈥檛 stop moving.
Previous work hinted that the brain, not eye movements, caused the pattern to dance: people viewing similar images mounted on contact lenses still saw the illusion even though the picture remained stationary relative to the eye.
Susana Martinez-Conde and her colleagues from the Barrow Neurological Institute in Phoenix, Arizona, think that natural tiny eye movements called microsaccades may have persisted due to slight movement of the contact lens on the eyeball.
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To see if this was true, they asked three people to view Isia Leviant鈥檚 Enigma (above) while cameras captured their eye position 500 times per second. The volunteers had to press a button when the trickle appeared to slow down, and release it when it sped up.
The illusion became more pronounced when their eyes flickered over the image at a faster rate, and vanished when their eyes slowed down, showing that eye movements did indeed create the illusion (Proceedings of the National Academy of Sciences, ). 鈥淲e can now rule out the idea that the illusion occurs solely in the brain,鈥� says Martinez-Conde.
The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
