All people can be considered as distributed along a spectrum, with the type identified by Dr. Leo Kanner in the 1940's at the one end and non autistic people at the other. Kanner type autists are generally considered low functioning,
tend to have low intelligence and will always require highly specialised support.

A third type of people known as higher functioning autists and identified by Dr. Hans Asperger,
 can be found centrally placed on this spectrum.

Traditional literature has depicted autism as accompanied by a "Triad of impairments", concerning social understanding, imagination and communication. As the spectrum is a continuum, the line between autists and non-autists is sometimes blurred and an autistic spectrum disorder (A.S.D.) will normally only be diagnosed when these issues are causing a relevant degree of detriment. A further affect of this blurring is that the triad of impairment model is limited when it comes to an in-depth understanding of medical autism, as most non-autists also experience these issues to some degree.

There are many differences between autists, but there are also shared traits.
The most essential of these is the fact that they only have access to a single channel of attention.

They tend to be able only to give attention to one thing at a time.
Thus they do not have "self awareness" (or similarly, "theory of mind") in the usual
sense as this requires simultaneous processing of a primary self and a secondary self that is aware of the first. Such meta-cognition is what distinguishes Homo sapiens from the other species because they are neurologically sapient, or "neurosapient", having access to multiple channels of attention. Their world is automatically filtered into key parts which are then imaginatively reassembled, as a vision of the future, or a comparative or empathetic insight.

Lacking this capacity autists are frequently alientated and often experience profound difficulties getting their social needs met.