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A Face-Off on Brain Studies / How we recognize people and objects is a matter of debate

SCIENTISTS TRYING to understand how the brain responds to

visual objects can't agree on what they see. At the heart of this controversy

is the human face and how the brain perceives it.

The brain tissue in question-which becomes activated when people look at a

face-is called the fusiform gyrus. In a brain scan, this area lights up, or

becomes active, more powerfully than it does when volunteers look at other

objects. Some scientists believe that the fusiform gyrus was designed

specifically to help humans recognize faces.

But more recently, a number of new studies suggests that this brain tissue

is more likely called on for the processing of a visual skill. Yes, it is used

to help people recognize faces, but as a skill, one that people have been

practicing over and over again since birth.

Scientists made the connection between the fusiform gyrus and its role in

the recognition of faces after several dozen patients with damage to this

tissue lost their ability to identify once- known faces. When high-resolution

brain scans came on the scene, it was time to figure out whether this tissue

was in fact specialized for faces.

At the Cognitive Neuroscience Society meeting in Manhattan last week, a

panel of scientists on both sides of the debate presented their arguments.

On one side is Nancy Kanwisher of the Massachusetts Institute of

Technology, who first proposed that the fusiform gyrus was specifically

designed to recognize faces-and faces alone-based on her findings using a

magnetic resonance imaging device. Then, Isabel Gauthier, a neuroscientist at

Vanderbilt University in Tennessee, talked about her research, showing that the

fusiform gyrus lights up when looking at many different kinds of objects

people are skilled at recognizing.

The debate has been going on for years. Gauthier, during her doctoral

student days at Yale, asked Kanwisher whether she could spend some of her

post-doctoral training in Kanwisher's laboratory at MIT. Gauthier's doctoral

work had shown that the fusiform gyrus becomes activated when people become

expert at looking at certain objects-faces, chairs, cars-any category where

there are many visually similar objects.

In a series of experiments carried out during her tenure at MIT, Gauthier

did brain scans of 19 men who were either expert in cars or birds. As she

expected, this area of the brain, the fusiform gyrus on the right side, became

activated when the men looked at familiar faces, but it also became active when

the bird-watchers looked at birds or car enthusiasts looked at vehicles.

"There is no good evidence that humans have an innate specialization for

faces," Gauthier said during a recent telephone interview.

It wasn't Gauthier's intention to prove Kanwisher wrong, but she felt they

both would learn a lesson. "In science, we rarely work with people who disagree

with us," Gauthier explained. "It pushes you to look at your data in many

different ways. It wasn't always easy. In the end, we still disagreed, but it

was a valuable experience."

Kanwisher, a professor in the department of brain and cognitive sciences at

MIT, says she stands by her data and that of others who have had similar

findings.

"The fusiform responds much more strongly to faces than to any other

object. Its primary role is in the recognition of faces," Kanwisher said.

What the area actually does when it looks at a face is still not known. It

could be that it just recognizes faces as a category, or it could actually help

the person distinguish individual faces, Kanwisher said.

She said that patients without the ability to recognize faces do not have

difficulty recognizing other objects they are familiar with.

One patient with diffuse brain damage, detailed in the work of Morris

Moscovitch at the University of Toronto, has difficulty recognizing objects,

but his ability to identify faces remains solid. "It shows that these two

functions are separate," Kanwisher said.

The MIT scientist declined to be a part of Gauthier's published results,

which appeared last year in Nature Neuroscience.

At the heart of the issue is the hope of unraveling the mystery of visual

perception.

"I don't think anyone can be equivocal on any side of the debate," said

Moshe Barr, a scientist at Harvard who moderated the debate. "There is more

than meets the eye. And the jury is still out."

Gauthier's new study suggests that the processing of facial information

may, in fact, be a skill that some people just don't practice.

In a new study, which appears in the April issue of the Archives of General

Psychiatry, Gauthier teamed with lead investigator Robert Schultz of the Yale

Child Study Center to test whether this region of the brain would behave

differently in people with autism. According to the study, the autistic people

did not have more activity in this region for faces when compared to other

objects. Gauthier thinks this makes sense if her theory is correct that this

area gets strengthened with practice. People with autism generally don't look

at faces, Gauthier said, adding that the fusiform gyrus finding is not a cause

of autism, but an effect of the underlying biology of the disorder.

James Haxby of the National Institute of Mental Health has studied how the

brain recognizes many categories of things-faces, houses, shoes, chairs, etc.

"We see a unique pattern with each category that might help us explain how the

brain represents objects," Haxby said. "Our findings suggest that the

representation of faces and other objects overlap."

He finds that even weak brain signals in this region are important to the

visual representation of objects. Many brain mappers have focused on large

responses and failed to factor in these weaker responses, Haxby said.

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