If you look at this wheel out of your peripheral vision, you should see it flicker or strobe a bit. (To me, it almost looks like a fast pulsating motion, coming from the center of the wheel.) And that's neat. Optical illusions are usually pretty neat.
But, as the blogger Neuroskeptic writes, there's some reason to think that what you're seeing might be something even more awesome than just your brain being misled. A study published this month in The Journal of Neuroscience suggests that the flickering is actually a visual representation of the rhythmic alpha waves that are constantly pulsating through your brain.
Alpha (α) waves are rhythmical electrical fields generated in the brain. They cycle with a frequency of about 10 Hz (ten times per second) and are strongest when you have your eyes closed, but are still present whenever you're awake.
When Hans Berger invented the electroencephalograph (EEG) and hooked it up to the first subjects in 1924, these waves were the first thing he noticed – hence, "alpha". They're noticable because they're both strong and consistent. They're buzzing through your brain right now.
But this raises a mystery – why don't we see them? Alpha waves are generated by rhythmical changes in neuronal activity, mainly centered on the occipital cortex. Occipital activity is what makes us see things. So why don't we see something roughly 10 times every second?
Neuroskeptic goes on to explain why the scientists think the flickering wheel is alpha waves — and why he's not totally convinced that they're right.