Humans are extremely adept at recognizing faces. But why is this?
Some scientists believe that our brains have unique functions that specialize only in face recognition. Others say that facial recognition comes from the same brain mechanisms used in other areas of visual skills, such as our ability to recognize different types of animals.
To settle this dispute, researchers from Harvard and Dartmouth administered tests to patients suffering from prosopagnosia, or “face blindness.”
During the study, published in the journal Proceedings of the National Academy of Sciences, patients with prosopagnosia did just as well as those without the disorder when asked to distinguish between highly similar objects.
However, when asked to learn a set of faces under the same conditions, prosopagnosia patients performed poorly. This suggests that prosopagnosia is tied to damage in a brain mechanism fully devoted to face processing.
“What we wanted to do was to test a key prediction of the ‘expertise’ hypothesis,” said Constantin Rezlescu, Ph.D., a postdoctoral fellow in psychology and the study’s first author.
“The expertise hypothesis predicts that when there is impairment in facial processing, you should also see impairment in processing other objects of expertise, because if the mechanisms are the same, any damage should affect both faces and other objects. Our findings, however, show a clear dissociation between participants’ ability to recognize faces and their ability to recognize other objects.”
The researchers then trained two prosopagnosia participants to become “experts” in recognizing 20 computer-generated objects designed to engage the brain in the way that faces do.
These computer-generated objects, called “greebles,” could be grouped into “families” based on their body types and shared a limited number of slightly different limbs arranged in a common pattern. To sort greebles, Rezlescu explained, participants must detect those subtle differences, similar to the way humans recognize slight differences in faces.
“These are very commonly used in psychology,” Rezlescu said. “One of their major uses is to investigate this expertise hypothesis … because supposedly it only takes people seven to 10 hours of training to become expert at recognizing them.”
Participants with face blindness performed as well as the control group in recognizing greebles, but they still struggled to recognize faces and scored far below participants without the disorder.
“In the real world, you may have experience for 10 years or more with objects that you become an expert on,” said Rezlescu. “But it is important to note that a great deal of the evidence that was claimed to support the expertise hypothesis comes from studies involving greebles, and what we found is that cannot be true.”
Source: Harvard University