Researchers have pinpointed areas of the human brain most sensitive to physical borders, like the curbs and walls we rely on as we navigate through the world.
They found one distinct brain region that reacts when the visual boundary has a vertical structure, like a curb or a wall, and another that reacts only when the boundary is tall enough to impede someone’s movement. The findings appear online in the journal Neuropsychologia.
“There is something giving ecological validity to a boundary—even a very small one,” says author Soojin Park, assistant professor of cognitive science at Johns Hopkins University. “The boundaries in an environment hugely influence how we move within it. We wondered, what’s the neural mechanism behind that?”
Park and former graduate student Katrina Ferrara monitored the brain activity of 12 subjects as they were shown images of objects displayed on a flat mat, on a mat surrounded by a low curb, and on a mat surrounded by a tall wall.
The researchers used functional magnetic resonance imaging to watch as activity in the visual processing areas of the subjects’ brains increased as the size of the boundaries increased. When the subjects saw the curb, however, even though it was only an inch or two tall, the brain reacted almost as vigorously as when the subjects saw a full wall.
“The curb is so important and the brain is so sensitive to it, brain activity jumps significantly when someone sees one,” Park says. “There’s something very important about having that three-dimensional vertical structure.”
The reaction was the same even when the researchers changed the look of the mat, curb, and wall, or the type of object displayed.
The part of the brain that reacted to the visual and spatial structure of a boundary when subjects saw a curb or a wall was the “parahippocampal place area.” This region responds preferentially to images of scenes and places over other objects or faces.
It was the “retrosplenial complex” that reacted when subjects saw a boundary tall enough to be an obstacle. Just like the parahippocampal place area, this region responds preferentially to scenes, but recent research found that this region is important for spatial navigation rather than visual analysis of individual scenes.
The National Science Foundation and the National Eye Institute supported the work.
Source: Johns Hopkins University