In Brief

A team of psychologists has refuted a long-held theory of how the brain distinguishes between objects, and their various shapes and sizes. Until recently, many had theorized that we use the same brain mechanism to recognize objects--to decide by looking at them if they are the same or different--and to mentally rotate them--turn around and compare them using our mind's eye, or "mental sketchpad." Now, the results of a new study suggest that people activate different brain circuitry in object-recognition and mental-rotation tasks. The findings appear in the journal Neuron (Vol. 34, p. 161-171).

In the study, led by Isabel Gauthier, PhD, assistant professor of psychology at Vanderbilt University, researchers used functional magnetic resonance imaging to examine brain activity of 15 participants as they performed two types of judgments. In a mental rotation task, participants had to decide if pairs of complex geometric objects were mirror images of each other. In an object-recognition task, they had to decide if objects had the same shape.

In line with previous findings, mental rotation activated the dorsal pathway in the parietal lobe, which showed increasing activity as differences in the orientation of objects grew bigger. But, during object-recognition tasks, activity in the dorsal pathway decreased, and instead increased in another part of the brain: the ventral pathway, particularly in part of the fusiform gyrus. "This suggests that very different parts of our visual system are recruited when making these judgments, despite similar behavioral responses," says Gauthier.

If replicated, the study's findings could have strong implications for tackling brain and learning problems, says Gauthier. "When someone has brain damage in the visual system, this can help us know what to expect and where to help," she says. "And it may help us with learning and behavioral problems that aren't easily understood, as when a child has trouble with one type of visual task but not another."

--B. MURRAY