For any animal, it pays to be able to spot other animals in order to find mates and companions and to avoid predators. Fortunately, many animals move in a distinct way, combining great flexibility with the constraints of a rigid skeleton – that sets them apart from inanimate objects like speeding trains or flying balls. The ability to detect this “biological motion” is incredibly important. Chicks have it. Cats have it. Even two-day-old babies have it. But autistic children do not.
Ami Klim from Yale has found that two-year-old children with autism lack normal preferences for natural movements. This difference could explain many of the problems that they face in interacting with other people because the ability to perceive biological motion – from gestures to facial expressions – is very important for our social lives.
Indeed, the parts of the brain involved in spotting them overlap with those that are involved in understanding the expressions on people’s faces or noticing where they are looking. Even the sounds of human motion can activate parts of the brain that usually only fire in response to sights.
You can appreciate the importance of this “biological motion” by looking at “point-light” animations, where a few points of light placed at key joints can simulate a moving animal. Just fifteen dots can simulate a human walker. They can even depict someone male or female, happy or sad, nervous or relaxed. Movement is the key – any single frame looks like a random collection of dots but once they move in time, the brain amazingly extracts an image from them.
But Klim found that autistic children don’t have any inclination toward point-light animations depicting natural movement. Instead, they were attracted to those where sounds and movements were synchronised – a feature that normal children tend to ignore. Again, this may explain why autistic children tend to avoid looking at people’s eyes, preferring instead to focus on their mouths.
Alim created a series of point-light animations used the type of motion-capture technology used by special effects technicians and video game designers. He filmed adults playing children’s games like “peek-a-boo” and “pat-a-cake” and converted their bodies into mere spots of light. He then showed two animations side-by-side to 76 children, of whom 21 had autism, 16 were developing slowly but were not autistic, and 39 were developing normally.