Friday Illusion: How your mind can animate an image

Sandrine Ceurstemont, editor, New Scientist TV

Seeing an object move doesn't actually mean that it's moving. In this video, the psychedelic patterns might look like they're rotating, but pause the video and you'll see that they are actually static images.

This striking illusion, created by visual perception researcher Akiyoshi Kitaoka from Ritsumeikan University in Japan, is commonly known as the 'rotating snakes' and exploits a peripheral vision effect where motion is perceived in one direction due to gradual changes in brightness of segments in the pattern. Rounded edges also seem to enhance the illusion.

The brain trick was thought to occur when our eyes slowly move across the image. But now a new study by Susana Martinez-Conde from Barrow Neurological Institute in Phoenix, Arizona, and colleagues is uncovering that superfast eye movements are responsible for the phantom motion.

Since the effect isn't perceived continuously, the team tracked eye movements of volunteers just before they started to see rotation. They found that people usually blinked, or moved their eyes so quickly they didn't realise it, right before their brain was tricked. Conversely, their eyes were stable when they didn't perceive motion.

Gradual changes in contrast, such as those in the rotating snakes pattern, are rarely seen without actual motion, perhaps suggesting why our brain is confused. "As far as I know, there are no examples in nature of animals using camouflage or other patterning strategies to evoke this illusion," says Martinez-Conde.

If you enjoyed this post, watch hearts with a phantom pulse or see how you can brighten an image by moving your head.

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