Bit of Brain Physiology

The picture is taken from the BBC video and highlight the two areas that process information relevant in autism. When the researchers attach sensors to a variety of individuals and found that autistic people tented to process faces in the same area as others would objects. - This answers the question why autistic people do not recognise expressions of emotions. - "Autistics don't seem to instictively know that other people have thought of their own" Partly due to this and other factors, social difficulties are characteristic through the autistic spectrum.
Oliver Sacks most excellent book An Antroplogogist On Marsh answers many related question as well as it is a fantastically good fun read!