Autism has drawn the attention of many medical scientists throughout the course of history. Fascinated by the various levels of impairment determined by this complex neurological disorder - behavioral, emotional, communicational and cognitive, scientists have tried to clarify the notion of autism and its revealing signs. The most exhaustive research conducted upon this type of disorder belongs to Leo Kanner, an Austrian psychiatrist that focused on the study of autism and other related disorders. Kanner was the first scientist to establish an elaborate description of the disorder which he referred to as a syndrome.

In the 40's, Kanner came up with a clear model of diagnosis for autism, based on various experiments and elaborate research. Although Kanner's model of diagnosis is relevant and complete, nowadays it can also be confusing in the process of diagnosing autism. Therefore, various contemporary medical scientists had focused their careers on improving the model of diagnosis introduced by Leo Kanner, clarifying certain obscure aspects that he presented in the past.

It is very important to understand that people with autism don't follow the same pattern of impairment, and in fact, the development of the syndrome can greatly vary from a person to another. The severity of autism can alternate from mild to very pronounced and the syndrome can affect people on multiple levels. It is very difficult to correctly diagnose people with autism, as the syndrome can generate a multitude of abnormalities that might point to other neurological disorders. For instance, while some people with autism may present a pronounced impairment of their social skills, they may have an average emotional IQ and a high performance IQ. Other people with the syndrome may have a low performance IQ, but they may present higher levels of emotional intelligence and better social skills.

When Kanner first established his model of diagnosis, he stated that the disorder is very complex and its margins are very difficult to identify. Hence, he invoked that autism can affect some levels more than others. Kanner's model of diagnosis presented these following features:

- Impairment of social skills, from early childhood to maturity;

- Impairment of communication skills, which can vary anywhere from complete inability to develop speech to poor ability of initiating and maintaining a conversation. Kanner also noted echolalia and excessive questioning as autistic features;

- Very low responsiveness to external stimuli, exaggerated preoccupation with repetitive activities, stereotype behaviors;

- Good cognitive skills and memory;

- Good physical skills and muscle coordination.

Considering the fact that Kanner didn't clarify many aspects of the syndrome, contemporary medical scientists have focused upon simplifying his model of diagnosis. Although the features and the patterns of autism described by Kanner have been preserved, modern science attempted to establish clear criteria of diagnosis. Furthermore, in the late 70's, Rutter developed new controversial theories, claiming that autism shouldn't be separated by performance intelligence in the process of diagnosing the disorder.