Elizabeth Pellicano of the University of Bristol who took part in the study explained why this finding was significant.
"The faces we see in the world seem to be unconsciously coded in the brain as points in a 'face-space'. 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," she said.
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, with the precise characteristics of what constitutes an average face changing based on the experiences of looking at other people.
This 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".
For example, 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 researchers who carried out the study found that kids with autism don't experience the face identity aftereffect to the same degree that normal children do.
As a part of their study the researchers introduced two groups of children 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.
Supported by the Australian Research Council and the Experimental Psychology Society, UK, the study appears in the journal Current Biology.