A basic question about visual processing is whether single areas in the brain are responsible for recognizing only one object or many. Little evidence has cropped up so far for the latter view. In Friday's issue of Science, two different studies suggest that both mechanisms are at play depending on what you¿re looking at, hinting that the final answer may lie somewhere between the competing theories.
In one study, scientists found that a region low on the right side of the brain near the back called the extrastriate body area (EBA) had a stronger response under magnetic resonance imaging (MRI) to pictures of bodies and body parts, but not faces, than to inanimate objects. "These findings suggest that the EBA is a specialized system for processing the visual appearance of the human body," Paul Downing of the University of Wales and colleagues write. So far they have not found other regions in the same general area that dedicate themselves to other classes of objects.
Perhaps that¿s because such regions don¿t always exist. In the second study, James Haxby of the National Institute of Mental Health and associates found that faces, houses, cats, bottles and other man-made objects caused a number of regions in the temporal cortex to light up with varying intensities under MRI. Each object caused a unique pattern of responses, and the spots that had the strongest response to one object also responded to the others. Thus, the different regions appear to work together to identify different things.
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In a separate commentary published in the same issue, Jonathan Cohen and Frank Tong of Princeton University point out that these studies don¿t necessarily contradict each other. Although both camps have ways of viewing the other¿s results in terms of their own theory, "prudence dictates that neither extreme is likely to be correct," Cohen and Tong write. "We are likely to find that more detailed theories will naturally fall on intermediate ground."
