Perception test

Here. As John Derbyshire says, "Don't read anything, just watch the video." (via)

Update: It didn't take long for that to get yanked from Youtube. The original is still online, but you'll need a little setup: You will see some people in white shirts and some people in black shirts. Each group has a basketball. Try to count the number of times the people in white shirts pass the basketball. OK, now watch the video. (Java is required.) What was the number? Now read the first comment.

Update: Here is another version of this, with Simon Baker as Patrick Jane doing the setup. Regular Youtube, no Java required, only the usual FlashPlayer.

Update, Dec. 12, 2010: Big Think has an interview with Prof. Christopher Chabris of Union College on our illusions about our ability to perceive and remember. Chabris has written a book, with Daniel Simons, called The Invisible Gorilla, inspired by the perception test that inspired this post. At the book's website are a number of videos with this among them.