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Do my eyes deceive me?

Updated: Jan 29, 2018

Written by Lakshini Mendis |


Everyone is familiar with visual illusions... but did you know that it's all in your brain?!


Apart from their Roman toilets, Puzzling World in Wanaka, New Zealand, is known for its mind-boggling optical illusions.


Here's an example! Make the video full screen and follow the instructions on screen...

Buzzy right? This is the motion after-effect in full force! 


This visual illusion occurs because of a phenomenon called motion adaption, which happens in your brain!


BrainHQ has a neat description about how vision works. When it comes to motion, basically, the visual cortex in your brain has brain cells that can be activated by certain movements.

For example, if you staring a visual stimulus that is spinning in a clockwise motion for a time (tens of milliseconds to minutes) with stationary eyes, then this increases the activity of your "clockwise" brain cells by a certain amount above baseline.


After a while, however, your "clockwise" cells decrease their activity, because they adapt to the motion. This adaptation basically allows you to register new stimuli. This makes sense from an evolutionary point of view, since you were probably safe from something that was moving but didn't attack you within a few seconds.

When the movement stops, however, the brain cells responding to the movement decrease their activity by the initial amount. This means that the activity of the "clockwise" brain cells is now below baseline. Since the activity of "anticlockwise" brain cells, which is at baseline (because it is not being stimulated), is now relatively higher than the "clockwise" brain cells, for a time, you'll see everything spinning in an anticlockwise direction... at least, until your "clockwise" brain cells return back to baseline!


This why you saw the visual illusion above!


You can also check out the explanation behind colour after-effects here!

Want more optical illusions? Check out this site.

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