>> NARRATOR Should you trust your vision?
Professor Daniel Levin at Vanderbilt University
has a unique test that might make you skeptical.
>> DANIEL LEVIN What you do is look at a face
and then attempt to match a little square
with the darkness or lightness that you see in the face.
>> NARRATOR To do this, you need to come up with a sense of the average
or overall brightness you see in the face.
It sounds simple, but it's harder than you'd think.
Try it for yourself.
Adjust the slider bar until the brightness of this square
matches the overall shade of gray you see in the face. Did you choose the same values for both faces?
You should have -- because these two faces
are the exact same shade of gray.
Their overall brightness values are identical.
Don't believe it? Most people don't at first.
>> DANIEL LEVIN I put a lot of effort into making sure the mean
brightness value of the image files was the same,
making sure that the mean contrast was the same,
making sure that the number of pixels in the image
was very similar...
So what's going on here?
Watch our video on Illusions at Work to learn the science
behind the illusion, and how our misperceptions can
color evaluations that go far beyond shades of gray.