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of a toy car, or on the way one part of the car feels or smells, as opposed to playing with it as it was intended (Lord et al., 1989). Affected individuals also may engage in repetitive, rit- ualized or routinized behaviors that are not required to com- plete the task at hand. Often, the child will feel anxious if this ritual is disrupted or blocked from being carried out. For example, a child may insist on reciting the names of his/her classmates every time they report about their day at school (Lord et al., 1989). Finally, individuals with autism may exhibit stereotyped motor mannerisms, e.g., hand flapping or finger flicking or twisting (Lord et al., 1989).
Although the set of core behaviors described above are associated with a diagnosis of autism (American Psychiatric Association, 2000), Lord and colleagues (2000) note that pro- files of behavior will vary for affected individuals, and even within an individual, with the behavioral repertoire changing as a child develops.
Pervasive developmental disorders
In addition to autism, there is a range of related disorders that share the primary deficits in social reciprocity and com- munication. The disorders that fall under this general umbrella of Pervasive Developmental Disorders (PDD) (American Psychiatric Association, 2000) include Childhood Disintegrative Disorder, Asperger syndrome, Rett syndrome and Pervasive Developmental Disorder—Not Otherwise Specified (Lord et al., 2000).
Childhood Disintegrative Disorder (CDD) differs from autism in that affected children exhibit a serious regression in multiple areas of functioning following normal development for at least two years. The profile of behavior shown by chil- dren with CDD includes a significant loss of interest in the environment and lack of social and emotional reciprocity and language skills. In addition, repetitive motor movements such as hand flapping and finger flicking emerge in this pop- ulation. Children also exhibit restricted interests and activi- ties (Lord, et al., 2000). CDD is usually associated with men- tal retardation in childhood consistent with the significant, progressive loss of skills in all areas of functioning (American Psychiatric Association, 2000).
Another disorder under the PDD umbrella, Asperger syndrome, is closely related to autism. While individuals affected with Asperger syndrome share deficits in social rec- iprocity and interaction, cognitive and linguistic skill is rela- tively spared, with no evidence of significant delays in these areas in early development (American Psychiatric Association, 2000). Although individuals affected with Asperger syndrome are interested in the social environment, they are impaired in the ability to read social cues and show great difficulty with pragmatic rules when communicating, e.g., by speaking in a particularly loud voice or discussing socially inappropriate topics.
Rett syndrome, a pervasive developmental disorder which primarily affects girls, shares common characteristics with autism early in development, including deficits in social, cognitive, and language skills, as well as stereotyped behav- iors (Glaze, 2004). However, there are several symptoms spe- cific to Rett syndrome, including loss of hand skills, problems
with gait, deceleration of head growth, and breathing and motor problems that allow it to be differentiated as a distinct disorder from autism (Lord et al., 2000; Mount et al., 2003).
Finally, Pervasive Developmental Disorder—Not Otherwise Specified is a category for those with deficits in the areas of social interaction, communication, or restrict- ed/repetitive interests, but who do not meet the criteria for autism because of atypical time of onset, profile or severity of symptoms (American Psychiatric Association, 2000).
Autism and language
The range of functioning for individuals with autism and related disorders varies from significantly impaired non-ver- bal individuals with mental retardation to individuals with above-average cognitive functioning and fluent linguistic skill. To describe the level of functioning within this range, researchers often characterize an individual’s behavior as low- or high-functioning (e.g., Jansiewicz et al., 2006). High functioning children with autism have IQ’s of 80 or above and the ability to speak (Williams et al., 2006). By extension, an individual who is low functioning will be in the mentally retarded range cognitively, without the ability to produce speech. Because the ability to speak is a significant skill in typical development, one important difference between low- and high-functioning status in individuals with autism appears to be whether or not an individual has productive speech. Moreover, the development of productive speech prior to the age of 5 is associated with better prognosis with respect to symptomatology (Rutter, 1983).
Auditory speech perception
The ability to perceive and produce speech is founda- tional in human communication from the earliest points in development. Thus, fundamental, basic problems in the processing of speech sounds create significant deficits in language and social functioning throughout development. One likely source of the marked impairment in language across the range of individuals with autism is a deficit in speech perception; however, the role of perceptual process- ing in this population has not been extensively examined. The available evidence indicates that individuals with ASD show atypical responses to speech and vocal sounds, (Gervais et al., 2004). In addition, affected individuals show deficits in understanding (receptive language functioning, Koning and Magill-Evans, 2001) and producing language (expressive language functioning, Howlin, 2003). Further, children with ASD have atypical asymmetry in brain regions associated with language, with greater volume in the right hemisphere, rather than the left (Herbert et al., 2002). Finally, visual influence on heard speech appears to be impaired in children with ASD (DeGelder et al., 1991; Massaro and Boesseler, 2003; Williams et al., 2004). In par- ticular, because of their severe limitations in productive lan- guage, non-verbal individuals with autism have been vastly under-represented in perceptual studies of speech. Because language ability is the key prognostic factor for long-term outcomes among children and adults with ASD (Lord and Venter, 1992), it is critical that we examine speech percep-
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