If you ever create a slideshow of portraits, you might want to avoid showing them aligned side-by-side with a gap in between. The video above shows a crazy optical illusion that researchers have dubbed the “Flashed Face Distortion Effect”. By flashing ordinary portraits aligned at the eyes, the human brain begins to compare and exaggerate the differences, causing the faces to seem hideous and ogre-like. Researcher Matthew Thompson writes,
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.
Here’s a second video showing the same thing: