
The McCollough Effect - geographomics
http://www.cheswick.com/ches/projects/me/
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georgemcbay
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.

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dag11
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?

~~~
Houshalter
I also experienced this and saw the image a few months ago. That the effect
lasts that long is sort of unsettling.

~~~
cypherpunks01
Yep, wikipedia cites a 1975 study "Extremely long-term persistence of the
McCollough effect" in saying that the effect can last up to three months in
some cases, after prolonged exposure.

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danielrhodes
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.

~~~
georgemcbay
This (what you described) is basically how most optical illusions of the type
of "look at this thing then look at this other thing" work, but this one is a
lot stranger than most in that the effects of it can reportedly last for up to
3 months.

I can't vouch for that directly, but I'm still seeing it an hour later and
some other responses here have mentioned that they actually are still seeing
it months later.

Other optical illusions that rely solely on the mechanism you're talking about
fade in under a minute.

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

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

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

~~~
cjg
Thanks, I much preferred your full screen version to the small ones on the
post. However, you've swapped the pink and green round compared to the
original.

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jacquesm
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.

~~~
Someone
_" I know what you are thinking: this is a simple afterimage effect. If you
think so, walk away from your terminal until you think the after image should
be gone. Go home and try it in the morning. Then take a look. Or better,
simply rotate the image. Well, maybe that isn't so simple with a CRT, but you
could rotate your head."_

What you describe is a simple afterimage effect
([http://en.m.wikipedia.org/wiki/Afterimage#Negative_afterimag...](http://en.m.wikipedia.org/wiki/Afterimage#Negative_afterimages)).

The MacCullough effect is different because it lasts much longer (Wikipedia
claims 3 _months_)

The McCullough effect is thought to be due to adaptation of edge detectors.
'Normal' after images are thought to be caused by adaptation of cones.

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the_cat_kittles
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.

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raldi
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.

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maaaats
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.

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thisjepisje
[https://news.ycombinator.com/item?id=8119144](https://news.ycombinator.com/item?id=8119144)

