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The journal Perception reports on an interesting visual effect called the “Flashed Face Distortion Effect.” Apparently an undergraduate student was working on setting up an experiment that required a series of faces all scaled in such a way that the eyes of each image aligned. As he flipped through the images, he noticed that some of the faces began to appear distorted in unusual ways. Researchers are now working on experiments to shed more light on exactly what is happening in the visual processing system to create the effect.

Abstract from the Journal Perception

We describe a novel face distortion effect resulting from the fast-paced presentation of eye-aligned faces. When cycling through the faces on a computer screen, each face seems to become a caricature of itself and some faces appear highly deformed, even grotesque. The degree of distortion is greatest for faces that deviate from the others in the set on a particular dimension (eg if a person has a large forehead, it looks particularly large). This new method of image presentation, based on alignment and speed, could provide a useful tool for investigating contrastive distortion effects and face adaptation.

The video above with two images side by side (from one of the authors of the paper) seems to make the effect even stronger than watching a single video with one face in the center. Something to do with peripheral vision perhaps?

In the full paper the authors report that the ideal presentation rate for the images is around 4-5 faces per second. If the images are not eye-aligned or presented to slowly or quickly the effect is not as strong. Inserting a break between faces makes the effect nearly go away.

They go on to suggest that the effect is most certainly related to something called the “face distortion after effect” first reported on in 1999. If presented with a face that has been artificially distorted in some way for a few seconds followed by a neutral face, the neutral face appears distorted in the opposite direction. So viewing a happy, sad, fat, etc., face followed by a neutral face will cause it to appear sad, happy, thin, etc.

These kinds of effects are not limited to faces. In 1998 researchers demonstrated that a briefly flashed line distorts a circle into an ellipse that appears elongated at 90 degrees to the line orientation.

In the single face video below the effect does not seem to kick in for me for at least 15 seconds or so. I like to focus on the nose bridge so my eyes don’t move around. That seems to kill the effect for me as well.