More good stuff for people who like visual ("optical") illusions (previously): A nice Scientific American article, a particularly creepy illusion, and a link to the "Best visual illusion of the year" contest. Given that the eye/mind/brain is so easy to trick, a person might wonder what's really out there in the world.
posted by cogneuro on Aug 28, 2008 - 26 comments

"Over and over he scoops up a chick with his left hand, expels its droppings with a squeeze of his thumb, opens its vent with his fingers, peers through the magnifying lenses attached to his spectacles and determines its sex." It's a dirty job (YT). Sexing chicks early is important so that the cockerels can be separated and culled^ or fed to be broilers^. The obvious differences take weeks to develop, so when the vent sexing method was developed in Japan in the 1920s, professional chicken sexers became sought after. [more inside]
posted by parudox on Nov 19, 2007 - 37 comments

Porn can make you go blind. Kinda.
posted by gottabefunky on Aug 22, 2005 - 40 comments

The McCollough effect is a visual illusion somewhat similar to regular color aftereffects, but the working mechanism is different, and despite a wealth of theories, not entirely explained. Once the effect is established, it does not seem to go away and can last for days or even weeks. Proceed at your own risk.
posted by ikalliom on Apr 10, 2004 - 22 comments