What we think we perceive in the present moment is far from everything we actually perceive. We’re guided by more than just the things we’re aware of. Even someone in deep concentration who believes they’re focusing on nothing else may not realize that their brain is constantly shifting back and forth between the conscious information they’re focusing on and unconscious information that never reaches awareness.
The human brain is thought to switch between processing conscious and unconscious information extremely fast, about 15 times per second, and only a fraction of the information it processes ever reaches conscious perception. Neuroscientists Janis Hesse and Doris Tsao of the University of California, Berkeley, wanted to learn why some neural activity becomes consciously available and some does not, so they studied what happens when the brain is faced with conflicting images. To do this, they needed a situation in which the physical stimulus stayed the same throughout the experiment while perception changed. With this setup, any differences in neural activity could be attributed to perception rather than to the stimulus itself.
One way to create such a situation is to show a different image to each eye. In binocular rivalry, each eye is shown a conflicting image, and the observer can consciously perceive only one image at a time. In a related phenomenon known as binocular flash suppression, the image first shown to one eye is suddenly suppressed, and becomes invisible, when a second image flashes before the opposite eye and is perceived instead. Neurons that respond more strongly to one type of image fire more when that image is perceived, even though both images are physically present. What especially puzzled the researchers was why these same neurons, while responding to the perceived image, still hold onto information about the suppressed one.
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