"The eye and brain can sometimes play funny games. Look at this front cover
image on the latest edition of the journal Science. "
"Observers were asked to move forward and backward in front of paintings and
say when they the nose emerged from the canvas.
These "critical distances" were recorded for each observer. Pelli also
measured the size of the blocks making up the painting, and calculated the
angle from the observer's eye at the critical distance.
To his surprise, this critical angle was always about 0.3 degree, for all
the paintings, despite their great variety in face size, block size, and
number of blocks per face."