Which Side Are You On? How the Brain Sees Borders

In the classic “Rubin’s vase” optical illusion, you can see either an elaborate, curvy vase or two faces, noses nearly touching. At any given moment, which scene you perceive depends on whether your brain is viewing the central vase shape to be the foreground or background of the picture.

Now, Professor John Reynolds and Senior Postdoctoral Fellow Tom Franken have made headway into understanding how the brain decides which side of a visual border is a foreground object and which is background. The research, published on November 30, 2021 in the journal eLife, sheds light on how areas of the brain communicate to interpret sensory information and build a picture of the world around us.

“The way that the brain organizes and generates a representation of the outside world is still one of the biggest unknowns in neuroscience today,” says Reynolds, holder of the Fiona and Sanjay Jha Chair in Neuroscience. “Our research provides important insights into how the brain processes borders, which could lead to a better understanding of psychiatric conditions where perception is disrupted, such as in schizophrenia.”

When you view a scene in front of you, individual neurons in the brain’s cortex each receive information about a minuscule region of the scene. Neurons receiving information from the border of an object thus have little initial context about which side is foreground. However, scientists previously discovered a set of cells that very quickly signal which side of the border belongs to the object (” border ownership”); after all, depth perception and the ability to pick out objects in front of you is critical to survival—is that a curb or a shadow, a rock or a cave?


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