Watch this video while staring at the cross in the centre, and you'll see bulbous foreheads, gigantic noses and terrifying eyes. Watch it again while looking at the faces, and you'll see they're perfectly normal pictures of attractive Hollywood actors. What the hell?
In fact, this is part of a research project by Matthew Thompson which investigates how the brain compares and exaggerates the differences between two faces when they're briefly flashed up on screen alongside each other. Writing on his website researcher Matthew Thompson explains:
"Like many interesting scientific discoveries, this one was an accident. Sean Murphy, an undergraduate student, was working alone in the lab on a set of faces for one of his experiments. He aligned a set of faces at the eyes and started to skim through them. After a few seconds, he noticed that some of the faces began to appear highly deformed and grotesque. He looked at the especially ugly faces individually, but each of them appeared normal or even attractive. We called it the "Flashed Face Distortion Effect"...
"The effect seems to depend on processing each face in light of the others. By aligning the faces at the eyes and presenting them quickly, it becomes much easier to compare them, so the differences between the faces are more extreme. If someone has a large jaw, it looks almost ogre-like. If they have an especially large forehead, then it looks particularly bulbous."