A main part of Rain Man is Charlie coming to terms with Raymond’s autism, in the beginning he doesn’t even believe it , he thinks its fake, he then realises its real and a very stressful and hard thing to deal with, not only that, but he realises it comes with some incredible attributes such as Raymond’s eidetic memory.
Although i know a small few people who do have autism, i don’t know any that are particularly severe and so i thought it would be a good idea to do some research on the subject.
In a nut shell, Autism is a lifelong developmental disability that affects how a person communicates with, and relates to, other people. It also affects how they make sense of the world around them.
It is a spectrum condition, which means that, while all people with autism share certain difficulties, their condition will affect them in different ways. Some people with autism are able to live relatively independent lives but others may have accompanying learning disabilities and need a lifetime of specialist support. People with autism may also experience over- or under-sensitivity to sounds, touch, tastes, smells, light or colours.
Asperger syndrome is a form of autism. People with Asperger syndrome are often of average or above average intelligence. They have fewer problems with speech but may still have difficulties with understanding and processing language.
(taken from http://www.autism.org.uk/about-autism/autism-and-asperger-syndrome-an-introduction/what-is-autism.aspx )
The ability to recall images in great detail for several minutes is found in early childhood (between 2% and 10% of that age group) and is unconnected with the person’s intelligence level, Like other memories, they are often subject to unintended alterations. The ability usually begins to fade after the age of six years, perhaps as growing vocal skills alter the memory process.[A few adults have had phenomenal memories (not necessarily of images), but their abilities are also unconnected with their intelligence levels and tend to be highly specialised. In extreme cases, like those of Solomon Shereshevsky and Kim Peek, memory skills can actually hinder social skills.
The correct name is eidetic memory. The term speed reading is often misused too. An eidetic memory is the recall of written material.
Highly Superior Autobiographical Memory can also remember things like what shoes a stranger wore on a specific date, show MRI differences, and have trouble with social skills (or, dealing with people who have inferior memories; ie: only 2 of 55 in the US have successful marriages) as well as suffer from depression/introspection
(taken from http://en.wikipedia.org/wiki/Eidetic_memory )
Having eidetic memory is very rare. in fact, only 8 people in the world have been proven to have it, one being Kim Peek, who Raymond from Rain Man was inspired by.