Ever had trouble getting the audio synced up with the video on your computer? Get the right kink in your brain, and you could live your whole life that way.
One man began a new phase in his life when he looked at his daughter's television and noticed that the audio and the video were out of sync. He heard the words the people were speaking before their mouths moved. A second television in the kitchen was doing the same.
So were all the people speaking to him. Reality seemed to be experiencing a video delay. The man went to the hospital and was tested for brain injuries, all while hearing his doctors' disembodied voices and then seeing their silently moving lips. Although the doctors determined he wasn't in danger, they realized that something was wrong with his brain. After some testing, they found that they needed to delay audio information about 200 milliseconds in order sync it up with visual information. The man isn't pleased to have a tape delay for his life, but he's gotten used to it.
It's harder for other people. Some researchers speculate that children with severe autism could be having a version of same out-of-sync problem. Their brains may be unable to process visual and audio information at the same time. Not only could that lead to a sensory overload, but it could keep them from making sense of the world in the first place. The adult man had a lifetime to understand that a person's moving lips should produce a sound. If a child has never had a chance to associate auditory and visual input in sync, they have yet another challenge to overcome in understanding the world.
Imagine a world where floating voices told you something, and then suddenly a person near you began moving in such a way that you could tell they wanted your attention. It would be like attending a lecture while the person next to you was whispering in your ear. The lack of synchronicity might explain why many autistic kids cover their ears. While neurotypicals experience someone speaking to us as a single source of information, autistic people could be experiencing two different inputs at the same time.