Internationally, the most widely used definition of autism is based on the Diagnostic and Statistical Manual of Mental Disorders (DSM) published by the American Psychiatric Association. Although autism was first included in the third edition of the DSM in 1980, it was the fourth edition of the DSM (DSM-IV-TR), released in 2000, that placed "Autistic Disorder" in a group of five "Pervasive Development Disorders" (PDD) that also comprises "Rett's Syndrome," "Childhood Disintegrative Disorder," "Asperger's Syndrome," and "Pervasive Development Disorder Not Otherwise Specified (PDDNOS)."

Autism Spectrum Disorders (ASDs) (also referred to as PDDs) are brain-based developmental disabilities that affect a child's ability to communicate, understand language, play and relate to others. The ASDs affect an estimated 1 in 150 births (Centers for Disease Control and Prevention, 2005). This means that as many as 1.5 million Americans today are believed to have an autism spectrum disorder. Autism is typically diagnosed by three years of age; however, researchers here at CARD are currently working to detect the signs and symptoms of autism at the earliest age possible. By detecting autism at a young age, children can gain earlier access to intervention services.

A diagnosis of autism is made when an individual displays at least 6 of 12 symptoms distributed across three major areas:

• social interaction,
• communication, and
• repetitive/stereotyped patterns of behavior and interest.

Specifically, an individual with autism may have difficulty with social behaviors such as eye contact, the use of spoken words, may use gestures to enhance verbal communication, may use repetitve and steroetypical behaviors such as flapping the hands or persistently repeating words or phrases. Individuals with Aspergers syndrome display a slightly different behavior pattern than that of individuals with autism. These individuals have difficulties with social interaction, understanding social conventions, social use of language (e.g., they may be overly talkative, be overly focused on topics of their special interest, fail to give important background information because they have problems judging their listener's informational needs, and so on), and may exhibit the repetitive behaviors, unusual and intense interests, and be resistant to change. They acquire their language milestones on time, and have normal to superior cognitive abilities.

Children who do not meet the full criteria for autism or Asperger syndrome may receive a diagnosis of Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS). Children with autism, Asperger syndrome and PDD-NOS vary widely in abilities, intellectual functioning, and behaviors/interests. Therefore, it is important to focus on the individual child's behavioral and learning profile when making intervention decisions and recommendations.