The findings, from a study conducted by researchers at the Universities of Bristol, Florence, and Western Australia, might help to explain some of the core social deficits associated with the disorder.
"The faces we see in the world seem to be unconsciously coded in the brain as points in a 'face-space'," said Elizabeth Pellicano of the University of Bristol. "In the middle of that space is the average, or most typical, face, with more distinctive faces lying toward the periphery. Those more distinctive faces are easier to recognize than ones that are closer to average."
When people with normal abilities see a face, their brains automatically locate this new face in face-space on the basis of its deviations from the average--perhaps the face has bushier eyebrows, for example, or a greater distance between the nose and mouth. "The really neat bit is that the precise characteristics of what constitutes an average face are continuously updated based on our experiences in looking at other people," Pellicano explained.
Evidence of that flexibility stems from a phenomenon known as the "face identity aftereffect," in which looking at a particular face even briefly biases perception toward people who have the "opposite identity," she added. Upon seeing a person with thicker-than-average lips, the observer's idea of the typical face accordingly develops somewhat plumper lips. As a result, thinner-lipped people become more distinctive than they would have been before because their lips now differ more from the "norm." In practice, such shifting of facial perception occurs for all aspects of a face simultaneously, not just any particular feature.
The new study finds that children with autism don't experience the face identity aftereffect to the same degree that normal children do. In the study, kids were first introduced to two faces, those of Dan and Jim, each of whom they were told were "team captains." They were then shown faces that looked like Dan or Jim to varying degrees. Those other faces were created with a computer so that the two faces gradually morphed with the mathematically calculated average face.
The kids with autism were just as able to distinguish between faces belonging to Dan's "team" versus Jim's "team," researchers found. The children were then shown computer-generated faces representing characteristics that were the opposite of those belonging to either Dan or Jim. After seeing opposite faces, typical kids suddenly found it much easier to place Dan-like or Jim-like faces on their rightful team. But the improvement in recognition was much smaller for children with autism.
The findings suggest that autistic children don't update their perceptions in the way typically developing children do. "Since faces are important for interpersonal communication, these adaptive difficulties could help explain some of the social problems that confront people with autism," Pellicano said.
The researchers include Elizabeth Pellicano of the University of Bristol and University of Western Australia; Linda Jeffery and Gillian Rhodes of the University of Western Australia; David Burr of the University of Western Australia and Università Degli Studi di Firenze.
This work was supported by the Australian Research Council and the Experimental Psychology Society, UK.
Pellicano et al.: "Abnormal Adaptive Face-Coding Mechanisms in Children with Autism Spectrum Disorder." Publishing in Current Biology 17, 1-5, September 4, 2007. DOI 10.1016/j.cub.2007.07.065 www.current-biology.com