The McCollough Effect

After gazing for a few minutes at both grids, I do see the effect but the green is much more prominent for me than the magenta (which I see, but much less pronounced) despite gazing back and forth at both for about the same time.

The page would be a bit better if it incorporated some basic image controls, IMO, to allow you to rotate the image, zoom it, etc.

I downloaded the image and did some of that locally and zooming in and out is pretty interesting because the effect becomes less pronounced (for me, anyway) as I zoom out away from 100%. It seems like the size of the "haze" around the bars remains constant as you zoom even as the size of the black bars changes, so as you zoom in the effect becomes less and less pronounced until eventually the black bars get so big that it seems to disappear altogether.

When I first looked at the black and white lines just now, I already saw a faint green and magenta glow in them. I hadn't even looked at the colored images yet.

Then I remembered that several months ago I tried this. Could it have possibly lasted that long?

Citation needed on this: but from what I understand, the way your brain processes vision is that some of what you "see" is in fact the past. The visual cortex keeps recently seen things around and the incoming visual information is mixed with the past images to create the present (almost like compression in a video). Thus it would make sense that after staring at the green lines for awhile your brain is using past information when looking at new lines and hence the illusion.

For anyone who's interested in full-screen colored grids, I threw them together in CSS.

Green (horizontal) – http://codepen.io/ChristianBundy/full/iaAcq

Purple (vertical) – http://codepen.io/ChristianBundy/full/moshj/

I already have it without switching from the grids to the B&W images, just by concentrating on one and then the other I see fading aftereffects from the image I looked at before, takes a long time to fade to nothing.

Uncanny how reproducible that is. I need to look much longer at the coloured bars before that same effect starts to be present on the B&W image. It's almost as if the screen has burned in.

things like this always make me think about how things like great cooking, visual art and music (im sure other stuff too) have managed to implicitly understand complicated and nuanced behaviors of our senses.

I trained one eye as instructed, while closing the other, then rotated my phone 90° and trained the other eye.

The effect has lasted for hours: one eye sees green-horizontal-purple-vertical, and the other, the opposite.

Last time I tried this, even my tiled floor and the blinds on the windows suddenly had colors. I think it will be triggered by almost every kind of striped pattern.