Visual illusions show us that we do not have direct access to reality. They can also provide an inkling of the mental processing that delivers our experience of the viewable world.
Indeed, it is the processing happening inside our brains that is the basis for many illusions. Rather than delivering information from our eyes in nearly raw form as a camera would, the brain tries to determine what is actually out there – what are the shapes and the objects in the scene?
When the information entering the eye is ambiguous, the brain must make educated guesses. The three displays below demonstrate this in rather delightful ways.
The Illusion of Sex
In this illusion by Richard Russell, the same face appears to be female when the skin tone is made lighter (left image) and male when the skin tone is made darker (right image).
The illusion works because changing the skin tone affects the face’s contrast – the difference between the darkest parts of the face (lips and eyes) and lightest parts (the skin).
Even without consciously knowing it, our brains are attuned to the difference in contrast between the sexes, and so contrast is one cue the brain uses to determine gender. When other cues are removed, contrast can be the deciding factor.
Perhaps the most interesting thing about the illusion is that the contrast doesn’t simply help us work out the sex of the face - it provides an experience of “seeing” a face that is male or female. The use of the contrast cue is done by unconscious processes.
The image in our mind’s eye has incorporated information that we already hold, and uses this to resolve ambiguity in the image.