Thursday, November 15, 2012


A cool illusion, based on something or other about retinal behavior. (There's not really any green dots. The color doesn't change on the page, which you can sort of see if you don't look at the cross in the center. But looking at the center, the residual image is, briefly, green. I think I used to know the name of the effect.) Anyhow, at one point I figured I'd use this as the title picture for a relevant post. But in my less agitated, post-election state, I decided just to post it for its own sake.

And I thank the reader who sent it to me a while back. Was it Pieter? My memory ain't fer shit.

[Added]: from reader Brad Davis, PhD comes this explanation:

... color information at the retina is red, green blue (more or less, the absorption curves are notnearly that clean). The first synapse is in the lateral geniculate nu.cleus of the thalmus where this three color system becomes a four color sytem. there are neurons that have a steady state response rate which increase their rate for green and reduce their rate for red, and vice versa. There are similar cells for blue/yellow and for intensity. With the illusion, the change from red (magenta) to neutral results in an overshoot, the neuron responds too much or too little briefly. This accounts for many afterimages (There are effects in the retina as well, this just isn't one of them.)

Popular posts