To one part of the brain, a bathroom equals toilet plus tub.
In mental terms, certain scenes are sums of their objects, researchers report online September 4 in Nature Neuroscience. The results help explain how people quickly and accurately recognize complicated scenes such as playgrounds, kitchens and traffic intersections.
Much of what scientists know about vision comes from studies of how people see simple objects in isolation, such as a line floating on a white screen, says cognitive neuroscientist Dirk Bernhardt-Walther of Ohio State University. The new work, in contrast, deals with messy, real-world scenes. “It’s an awesome study,” he says.
A number of different brain areas are involved in telling us where we are, each relying on different types of information. In cases where the general outlines of a place offer little information, it appears, the brain homes in on specific objects within that space.
“A bathroom and a kitchen may have similar three-dimensional shapes of the interior, but the objects will tell you a big difference,” says study coauthor Sean MacEvoy of Boston College.
MacEvoy and Russell Epstein of the University of Pennsylvania measured the brain activity of 28 people viewing one of four scenes: a bathroom, kitchen, street intersection or playground. Participants then saw isolated objects associated with each scene, allowing the researchers to record the neural signature of each object. MacEvoy and Epstein focused on a particular part of the brain called the lateral occipital cortex, or LOC, which had responded to objects in previous studies.
When combined, the signatures of single objects closely matched the brain responses to entire scenes, the researchers found. For instance, the average LOC response to a stove and a fridge matched the response to an entire kitchen. To the LOC, these scenes are a simple combination of parts.
“I think it’s neat that a sum of the information from the objects is what makes up the scene, as far as the LOC is concerned,” Bernhardt-Walther says. “There is no additional magical ingredient. There’s no scene glue somewhere.”
But for scenes that don’t contain lots of telling objects, such as a desert or an empty stadium, the LOC may not be such a help. For more barren landscapes, the brain may rely on a region called the parahippocampal place area, or PPA, which is thought to help people take in whole scenes in a more holistic way, MacEvoy says.
Scientists don’t yet understand how these two systems work together to assess different kinds of scenes. Studying what happens in the brain when a person views a contradictory image might help illuminate how the brain interprets scenes, says cognitive neuroscientist Marius Peelen of the University of Trento in Rovereto, Italy. “If you put a sofa in the desert, you create a huge conflict of what you’re looking at,” he says, “whether it’s a desert or a living room.”