Strange Optical Illusion

On a close-up view, you can see on the left face, an angry man and on the right face, a woman with a neutral facial emotion. But further back, the faces change expression and even genders! if you squint, blink, or defocus, an angry man should substitute for the face of the woman and the left angry face should not be angry anymore. [Squinting hard worked best for me.]

This impressive illusion created by Dr. Aude Oliva and Dr. Philippe G. Schyns, illustrates the ability of the visual system to separate information coming from different spatial frequency channels. In the right image, high Spatial Frequencies (HSF) represent a woman with a neutral facial expression, mixed with the low spatial frequency (LSF) information from the face of an angry man. On the left, the face of the angry man is represented in fine details whereas the underlying female face is made of blur only ("blobs").

Be sure to read the research article [pdf], and there are more examples of hybrid faces in this pdf file and at the MIT Computational Visual Cognition Lab.

[Special thanks to my brother, from whose blog I copied this entire post.]