It’s not always wise to trust what your eyes are showing you. Recently, researchers have been making headway in understanding how communication within the brain allows our expectations to influence what we perceive.
The process of vision begins with an image forming on the retina in the eye, which then sends signals through nerves to the brain. These signals are then interpreted within the visual cortex of the brain. While scientists know a fair amount about the signals that go from the retina to the brain, much less is known about signals that work in the opposite direction. Some more recent discoveries suggest that the information carried by these feedback signals may use expectations to manipulate what someone observes.
To test this theory, researcher Tamara Watson of the University of Sydney experimented using a concept known as "binocular rivalry." Normally, the brain merges together slightly different images from each eye. When the images are extremely different, the brain experiences a rivalry between the two images, in which one eye’s image is perceived while the other is suppressed.
Subjects were shown images of walking figures made visible only by lights on their joints. At first, each eye saw different dots representing two different human forms, creating the expected binocular rivalry. The dots were then scrambled to enable each eye to see half of the two distinct figures, ending the rivalry.
Our brains generally do not recognize walking figures until well after the information from both eyes is fused. Watson’s study, published recently in Current Biology, reveals that once a walking figure is identified, it can cause signals from one eye to dominate while suppressing those from the other eye.
The researchers conclude that the brain’s expectation of seeing a walking figure between the dots is conveyed somehow to the earliest stage of the visual cortex, where signals from both eyes first join.
