Optical illusions show how we see
Visual illusions that show how we (mis)think
all of the pieces of our visual system work together to rapidly create a 3D
rendering of our surrounding environment. But just like detecting edges in the retina or creating 3D surfaces from
gradients of light in the neocortex, we don’t see everything around us equally.
We focus on what’s most important to us.We focus on faces or animals that might kill us and consume us.
example, in the ‘what’ pathway there is a cortical region called the fusiform
face area that is specifically designed to help us see faces. In analogous cortical areas in monkeys
(inferotemporal cortex) there are cells that respond to facial features such as
how far apart the eyes are, how big the mouth is, and how curved and angry the
eyebrows look. There are cells that
respond to what direction the head is faced. All of this requires many
assumptions, one of which is that people aren’t upside down.
upside down face illusion is based on 1) the assumption that faces are usually
right side up, and 2) that different parts of the face are processed
separately. The upside down face has the
eyes and mouth cut out and turned upside down (or rights side up, I guess).
Then when the image is rotated the eyes and mouth get turned upside down and
the whole face looks weird.
So at every level, whether it’s the
retina or the neocortex, the neurobiological basis of optical illusions
demonstrates how our visual system translates confusing ambiguous light
patterns into realistic 3D objects around us.It does this by making assumptions, and then sticking to those
assumptions for better or worse. It gets
things wrong every once in awhile (for example, if you go out of your way to
make an optical illusion), but 99.9% of the time it gets it right and it does
so in less than 300 ms. Optical illusions don’t show us quirks in the visual
system, they provide a glimpse at the complex neurobiological systems required
to turn squiggly, smudgy dots captured by the retina into a realistic, animated
3D world around us.