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.
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")
Credit to Aude Oliva (Massachusetts Institute of Technology, Cambridge, USA)
and Philippe G. Schyns (University of Glasgow, Glasgo,w UK)
The above two ambiguous faces, termed hybrid faces, are published in the journal Cognition, 69, 243-265, 1999. Elsever publisher