(There are many similar illusions, but I was unable to find the source for this exact one. If you know who created it, let me know in the comments.)
But why do our brains have such difficulty with images like this? It turns out has a lot to do with angles and colors, as this nifty post at Carlos Scheidegger's Visualization blog demonstrates. Using interactive sliders, you can adjust the parameters of a similar illusion to see how the image on the left looks normal, while the one on the right boggles the mind.
But if you want a real trip, click the "Engage" button near the bottom of the post. Whoa, indeed! Remember, you're looking at concentric circles, not spirals.
That's all for this week. Have a great weekend, and we'll be back on Monday!