01 April 2010

Color perception Thursday

I lifted this image from the brilliant Richard Wiseman. It illustrates another cool quirk about human eyes and their ability to perceive color.

Click on the image below and it will start its animation. Stare at the black dot in the center of the photograph.

Did you see it?

When the image changes, it's a black and white photograph, but your eyes should see it as a normal color image for a couple of seconds until your eyes adjust. Go back and try it again if you missed it.

What's happening there is what's called a negative afterimage. When you stare at something long enough, the cone cells in your retina adapt to the image and stop processing new information. They go into a feedback loop that continues to send information to your brain that's a copy of the information they've already sent.

Once the image they're perceiving changes, it takes them a couple of seconds to adapt to the new information. In the lag time, your brain can't make any sense out of the signals that it's getting so it more or less makes up what it expects to be there.

Afterimages are why you can't see colors accurately if you stare at them for too long.

Afterimages don't just work on still photos either. This one moves and it's cool beyond description.

Human eyes and human brains are amazing machines but they are fallible. It's important to know where the chinks in the armor are.


  1. With our Oregon waterfalls, a fave is to get visitors to just watch the water falling for several minutes, then quickly shift their vision to the cliffside adjacent to the waterfall. The cliffs seem to undulate upwards. They practically fall over.

  2. Who doesn't love a good motion afterimage. I took a physiology of the sense class in college a hundred years ago and we used to play with these kinds of perceptual missfires all the time. Fun!


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