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See Inside January / February 2010

Are Our Brains Wired for Categorization?

Our innate brain structure reflects how we classify the world around us

Picture a living thing—say, a dog. Now imagine a hammer. You just activated two different areas of your visual cortex, the brain region that processes eyesight. Thinking of a dog activates an area that deals with animate objects, whereas a hammer excites one that processes inanimate things. Now a new study shows something surprising: the same thing would have happened even if you had never seen a dog or a hammer before.

Psychologist Alfonso Caramazza of Harvard University and his team found that the visual cortex’s organization around these categories of knowledge is similar in sighted people and in individuals who were born blind. The finding challenges the long-held notion that the two separate processing areas exist solely as the result of learning to recognize the differences in the visual appearance between living and nonliving things, says cognitive neuroscientist Marius Peelen of Princeton University, who was not involved in the study.

Instead something else must be driving the visual cortex’s organization as well. That something could be connections to other brain areas, Caramazza suggests. From the visual cortex, information about living and nonliving objects is shuttled to different areas of the brain so as to trigger appropriate reactions. Animals, for example, could be dangerous, “but you don’t have to run away from a hammer,” he says. The new findings suggest that the wiring system that connects different areas of the visual cortex with appropriate regions in the rest of the brain is innate—it does not have to form gradually based on visual inputs. That means “the organization of the brain has to be understood in terms of our evolutionary history,” Caramazza notes. Our brain’s structure is such that we can distinguish prey and aggressors from other kinds of objects, and we have retained this structure even as we get “milk from bottles and meat from the butcher shop.”

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