autistic behaviour as epiphenomenon
One of the oldest behavioural findings in autism is the phenomenon of stimulus overselectivity, in which a person with autism responds only to one or a few elements of a complex stimulus.
Overselective responding can be explained in terms of slowed attentional shifting: if attention is stuck on one particular feature, other elements simply won't be noticed.

Overselective perception, in turn, can lead to a preference for ritualised, repetitive behaviour and to a failure to develop joint social attention, the ability to coordinate attention between external events and the people with whom those events are being shared.

One of my favourite explanations of the relationship between attention and social behaviour comes from Sean Barron's book There's a Boy in Here.
Barron was a child with autism who eventually developed communicative language, and as an adult wrote a book about his experiences.
He wrote: [see text above]

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`Physiological Studies of Attention in Autism: Implications for Autistic Cognition and Behaviour', Matthew Belmonte, 26 January 2002