শুক্রবার, ২১ সেপ্টেম্বর, ২০১২

Friday Illusion: Rotating snakes get a new twist

Sandrine Ceurstemont, editor, New Scientist TV

It's surely one of the most trippy illusions around: a static pattern of rotating snakes that appears to move before your eyes. But now Kazuhisa Yanaka from Kanagawa Institute of Technology and colleagues have added a new twist to the classic effect that makes the pattern seem to spin faster.

The variations involve shaking the static illusion and changing its colours (see video above). While rotating snakes in both colour schemes appear to move faster when jitter is added, a single direction of rotation is perceived with red and blue hues. However, in a different pattern shown later in the video, the illusion is only enhanced in the red version.

A recent study revealed that the static illusion is most likely caused by tiny eye movements called saccades rather than a slow, drifting gaze as was previously thought. So adding jitter could simply be accentuating the saccades, although colour also seems to play a role.

According to Yanaka, the effect of hue could have an evolutionary origin since our ancestors only saw two primary colours and couldn't distinguish between red and green. At that time, humans had to escape natural enemies like snakes, so illusory motion could have kept them safe by making them overly cautious.

Yanaka discovered the effect by chance when he was looking at the rotating snakes illusion online and moved the vertical scroll bar in his browser. The illusion was recently presented at the European Conference on Visual Perception in Alghero, Italy.

If you enjoyed this post, see how colour can warp a wheel's motion or how to colour an image with your eyes.

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