For example, symptoms and characteristics change with developmental maturity and vary with the degree of associated cognitive impairment (Filipek et al., 1999a). This evolving pattern of clinical features can make the differential diagnostic process very difficult in some cases. Nonetheless, the defining feature of autism is the presence of a distinctive impairment in the nature and quality of social and communicative development (influenced by the specific biological and environmental circumstances of the individual). It is this impairment that distinguishes autism from other neuro-developmental conditions (e.g., mental retardation, developmental language disorders, and specific learning disabilities). For example, whereas mental retardation is characterized by a pervasive developmental delay, autism is characterized by a distinctive impairment in the nature of social-communicative development. The prognostic significance of this autistic social dysfunction is underscored by preliminary studies that report a negative correlation between the severity of this social impairment and treatment responsiveness, at least with regard to social and linguistic growth following intensive, behaviorally based early intervention (Ingersoll, Schreibman, & Stahmer, 2001).
Additional complexity in the differential diagnosis of autism and related PDDs results from a wide range of accompanying abnormalities within cognitive, adaptive, affective, and behavioral domains of development, including mental retardation, deficits in executive functions, limitations in adaptive skills, learning disabilities, mood instability, stereotypic and self-injurious behaviors, anxiety disorders, and aggression (Hollander et al.; King, 2000).
The Autism of Early Infancy:
This is a normal condition. There is little awareness of the outside world as such, which is experienced in the mode of the infant's bodily organs, processes and zones. A normal infant emerges from this state because of an innate disposition to recognize patterns, similarities, repetitions and continuities. These are the raw materials for such mental processes as recognition, classification, object creation and empathy. Through these processes, the child builds an inner representation of commonly agreed reality and becomes self-conscious. The study of children who have failed to emerge satisfactorily from the state of normal primary autism brings home to us the complexity and delicacy of the time-consuming process of becoming aware of the world and its objects, persons and other minds.
The Autism Associated with Psychosis:
When things have gone grossly wrong with these early cognitive processes we say that the child is psychotic. The degree to which he is out of touch with reality distinguishes the psychotic from the neurotic child. However, it is important to make the point that the normal healthy infant who starts life by being out of touch with reality is not psychotic. But he is autistic.
Autism is a "spectrum disorder," meaning that it manifests itself differently in each child. Like a row of dominoes, if an early aspect of development is affected in a particular case of autism, other later-emerging aspects of development will be affected too. As a result, each case of autism presents a slightly different profile of learning abilities and learning disabilities. Each learning ability and each learning disability may influence how a