Most people assume we use our eyes alone to see the world. Not true: The brain plays a huge role.
The eyes receive light, and the brain finds the best way to interpret the light as objects and scenes.
What do you see below? Most people see an unfamiliar black object.
Yet if you look at the white regions close to the left and right sides, you can see portions of familiar objects — white seahorses in profile.
By testing people with many special pictures like the one above, my students and I found that before you see objects, your brain considers alternatives and then decides what you will see.
These alternatives compete outside of conscious awareness, so the viewer is aware only of the object that wins the competition. For the image above, the brain considers white seahorses as well as the unfamiliar black object. However, the black object wins the competition.
My students and I were the first to find evidence for this competition. To observe processes occurring outside of a person’s awareness, we have devised several methods.
Brain processes that occur before we perceive objects take place very quickly. We measured how long participants in our experiments took to respond to various pictures. When familiar objects are hidden on the outside of the image, we found people take about 15 to 40 milliseconds longer to respond.
We also found that for some time after the black object interpretation wins the perception competition, people take longer to respond to pictures of seahorses. It seems the loser of the competition is “down for the count.” The count is more than 100 milliseconds, but less than 500 milliseconds.
In collaboration with University of Arizona psychology faculty members John Allen and Paige Scalf, my graduate students Jay Sanguinetti and Laura Cacciamani and I measured brain activity via electroencephalogram, or EEG, electrodes placed in caps. We also used a brain imaging technique called functional magnetic resonance imaging. Each technique revealed that the brain registers the seahorses even when it rejects that interpretation.
The pictures we use are similar to the familiar vase/faces picture seen on the right side of the page.
Although for most pictures the same object wins each time, that’s not true for this one. This picture — known to change from profile faces into a vase and back again — is often considered unusual. It really provides clues to how the eyes and the brain work together in normal vision. The changeability of this picture indicates the competition between objects recurs if you look at an object long enough.
Not everyone responds to all images the same way. Some people do see the seahorses in the picture shown at the beginning of the article.
We don’t yet know why. Perhaps they looked at the outside first, or their life experiences led them to favor seahorses, or their brain decided the black and white regions were pieces of a tile pattern.
My students, colleagues and I continue to investigate the mysteries of unconscious processing in vision.