Autism is the best recognized and most frequently occurring form of a group of disorders collectively known as the pervasive developmental disorders (PDD). "It is diagnosed on the basis of abnormal social development, abnormal communicative development, and the presence of narrow, restricted interests, and repetitive activity, along with limited imaginative ability" (Baron-Cohen 1999). Autism is the result of an abnormality in the structure and function of the brain. Although technology still does not allow researchers to see much of how nerve cells grow or come together in the brain, or how information is passed from nerve to nerve, there is increasing evidence that the problems associated with autism and the other forms of PDD are the result of structural differences in the brain that arise during pregnancy--either due to something that injures the brain or due to a genetic factor that interferes with typical brain growth (Frith 1993).
The capacity to understand that others think the same way you do is a capacity called "theory of mind". Autistic children are very slow to develop even a partial theory of mind, and many never really develop it at all. Hand-leading is also used by other language-handicapped children, and by deaf children, but when they hand-lead, they combine gaze between the parent and the object with the hand-leading, making it a more social activity. Closely related to the observation that autistic children do not point or develop a theory of mind at the usual time is the observation that autistic children lack social referencing. Social referencing is an early form of social behavior that every parent recognizes: Usually social referencing first appears when the baby is about six to eight months old. "The theory of mind suggests that the key social, communicative and imaginative impairments which characterize this disorder result from an inability to represent mental states" (Frith et al 1994, p. 108). In thinking about the nonverbal communication of an autistic child, it is important to distinguish between nonverbal cues that the responsive parent just knows how to read (like a little boy who keeps playing, but holds the front of his pants when he has to go potty) versus intentional messages that the child is sending to the adult (like a little boy who looks at his mom with a pained expression and wiggles up and down while holding the front of his pants). True nonverbal communication involves a type of "mind-reading"--knowing that what you're thinking is somehow going to be conveyed to someone else through you facial expressions or gestures, and without the use of words. The main limitation of this theory is that simply put, a theory of mind is the belief or "theory" you hold that others have a "mind" capable of understanding things the same way your mind does. A lack of theory of mind results in unawareness of others' thoughts and feelings, and so contributes to the lack of interest on the part of autistic children in sharing their triumphs and failures with significant adults (Frith and Happe, 1994).
Another theory of autism is the extreme male brain theory. "The model depends on the notion of there being a "male brain", defined psychometrically" (Baron-Cohen 1999, p. 24). Researchers suppose that females and males and differ in cognition: "females are show faster levels