Nope, the text is not a gradient.
Dr. Angry and Mr. Smile
What
is the expression of the man on the left ? And the woman on the right?
Now, take
a few steps back or squint your eyes: how do their expression change?
On
a close-up view, you can see that the man on the left is frowning and
on the woman is calm. right face, a woman with a placid facial emotion.
But further back, the faces change expression and even genders! if
you squint, blink, or defocus, the angry man turns calm (left) and the
calm woman turns angry... and male (right).
This
illusion created by Dr. Aude Oliva and Dr. Philippe Schyns
illustrates the ability of the visual system to separate information coming
from different spatial frequency channels. These two hybrid faces are currently
on exhibit at the Exploratorium
in San Francisco. Read a scientific paper about them
Schyns
& Oliva, 1999.
Another Example: (this one from frowns to smiles)
There are spatial scales in which humans perceive objects (some more than others: eg. faces) differently. Those spacial scales are called the fine spatial scale and coarse spatial scale.
"...there is suggestive evidence that information at different scales can
support different categorizations of one face. However, the question remains of
whether information at any of these scales (e.g. LSF for the identity of faces) is
selectively accessed and used when relevant cues are also present at the other scale
(e.g. HSF), as they are with all naturalistic stimuli. In the face studies reviewed so
far, the evidence that information at a restricted bandwidth is sufficient for this or
that categorization does not imply that it is selectively accessed when all spatial
scales are available.
This experiment suggested that rather than a mandatory
use of one scale before the other, people can selectively attend to and recognize the
information of different spatial scales." (Schyns and Olivia, 1999)
Credits This illusion was invented by Philippe G. Schyns and Aude
Oliva of the University of Glasgow. It is featured on this web page:
http://cvcl.mit.edu/ , listed under 'Dr Angry and Mr Smiles'.
It is taken from Schyns and Oliva's paper,
"Dr Angry and Mr Smiles: when categorization
flexibly modifies the perception of faces in rapid visual presentations, Nov 1998".