An Indian-origin researcher at the Massachusetts Institute of Technology (MIT) has attempted to explain why autistic people fail to recognise faces as effectively as their normal counterparts, by studying why they often fail to recognise faces in photographic negatives.
Pawan Sinha, an associate professor of Brain and Cognitive Sciences, says that a person's eyes appear darker than the forehead and cheeks in nearly every normal lighting condition.
He believes that photo negatives are hard to recognize because they disrupt these very strong regularities around the eyes.
During a study, he and his colleagues asked subjects to identify photographs of famous people in not only positive and negative images, but also in a third type of image in which the celebrities' eyes were restored to their original levels of luminance, while the rest of the photo remained in negative.
Sinha says that the subjects had a much easier time recognizing such "contrast chimera" images, because the light/dark relationships between the eyes and surrounding areas were the same as they would be in a normal image.
He adds that similar contrast relationships can be found in other parts of the face also, primarily the mouth, but those relationships are not as consistent.
"The relationships around the eyes seem to be particularly significant," he says.
Sinha says that scientists studying face-perception skills in autistic children may find his observations interesting because such children are often reported to experience difficulties analysing facial information.
He points out that some studies have shown that those with autism tend to focus on the mouths rather than the eyes, which is why his study may help understand why such people have such difficulty recognizing faces.
The findings also suggest that neuronal responses in the brain may be based on these relationships between different parts of the face.
The team found that when they scanned the brains of people performing the recognition task, regions associated with facial processing were far more active when looking at the contrast chimeras than when looking at pure negatives.