Los Angeles, Dec. 11, 2006 -- Researchers in Southern California have isolated brain regions that respond selectively to the cues of gender, ethnicity and identity in faces. Using a novel adaptation technique, they found evidence for neurons that are selectively tuned for gender, ethnicity and identity cues in an area not previously thought to be associated with face processing. Led by researchers at the University of Southern California (USC), the work is a collaboration between USC, the Salk Institute for Biological Studies, and the University of California at San Diego (UCSD). The findings appear Dec. 11 in the Proceedings of the National Academy of Sciences.
"When looking at a face, its gender and ethnicity tends to be the first thing we notice," says Ione Fine, Ph.D., assistant professor of ophthalmology at the Keck School of Medicine of USC and the principal investigator of the study. "We become sensitive to these cues remarkably early in life. If you look at how pre-school children classify faces you find that these very young children pay attention to gender, ethnicity and age. In contrast, small children barely notice if a person is wearing eyeglasses. We wanted to see what was happening in the brain."
The experimenters relied on an adaptation technique. Over a period of three minutes subjects were adapted to a series of male Asian and female Caucasian face images. The researchers then interposed occasional female Asian and male Caucasian face images and measured how the appearance of these faces was altered by the previous adaptation. They found that adaptation altered the appearance of faces- adaptation to male Asian and female Caucasian faces made male faces appear more Caucasian and female faces appear more Asian.
The authors then used functional magnetic resonance imaging to measure brain responses using the same paradigm. This allowed them to isolate brain responses driven by very selective neurons tuned for both ethnicity and gender. As expected, they found brain responses to the female Asian and male Caucasian face images within regions in the fusiform gyrus, a brain area previously associated with face processing. More surprisingly, however, strong responses were also found within the cingulate gyrus, a brain area not previously associated with face processing. These selective brain regions also seemed to be sensitive to the cues of identity, suggesting that they may also be involved in recognizing individuals.
"A surprising percentage of the population -maybe 2 to 3% of the population- have a real inability to recognize faces or even tell if someone is a male or a female," says co-author Minna Ng, a graduate student at UCSD. "In the most extreme cases it's a clinical condition called prosopagnosia. Until now, most people assumed that difficulties with face recognition were due to cortical deficits near the fusiform gyrus. These data suggest that other brain regions may be involved. The fact that the cingulate gyrus is involved has some interesting implications for conditions like autism spectrum disorders."
The authors are now examining how we might develop this sensitivity to the subtle cues that define gender, ethnicity and identity. Children and adults generally aren't explicitly taught how to make these judgments; it seems to be an automatic process.
"Adults show large variations in how good they are at recognizing faces, and if you are bad at it, it can be very stressful and embarrassing," says Fine. "Perhaps if we have a better understanding of how face categorization develops, we can eventually develop ways of helping people get better at it."
Also participating in the study were Dr. Vivian Ciaramitaro and Dr. Boynton from the Salk Institute for Biological Studies, and Dr. Stuart Anstis from the University of California, San Diego.
This work was supported by National Science Foundation Integrative Graduate Education and Research Traineeship Fellowships.
"Selectivity for the configural cues that identify gender, ethnicity, and identity in human cortex." Minna Ng, Vivian M. Ciaramitaro, Stuart Anstis, Geoffrey M. Boynton, and Ione Fine. PNAS, 19552-19557 December 19, 2006 vol. 103 no. 51
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