voice

When we talk to people on the phone who we know well, we can often predict their physical gestures while they're talking, even if we can't see them. That's because we've seen them do it before, and because of cues from their voices.

A variety of characteristics are used to diagnose autism in children. Often, it's poor social and communication skills which others observe in children that compel parents to get a child tested. There are currently no unique biological indicators of autism.