not mentally retarded, a broader definition of autism that includes less impaired individuals, and greater educational opportunities for children with autism in the past two decades in many countries. It will be important to consider the effects of these possible shifts on interventions.

In school-age children, traditional measures of intelligence are more readily applicable than in younger (and lower functioning) individuals. Such tests have generally shown that children with autism exhibit problems both in aspects of information processing and in acquired knowledge, with major difficulties in more verbally mediated skills (Gillies, 1965; McDonald et al., 1989; Lockyer and Rutter, 1970; Wolf et al., 1972; Tymchuk et al., 1977). In general, abilities that are less verbally mediated are more preserved, so that such tasks as block design may be areas of relative strength. Tasks that involve spatial understanding, perceptual organization, and short-term memory are often less impaired (Hermelin and O’Connor, 1970; Maltz, 1981) unless they involve more symbolic tasks (Minshew et al. 1992). There may be limitations in abilities to sequence information cross modally, particularly in auditory-visual processing (Frith, 1970, 1972; Hermelin and Frith, 1971). There is also some suggestion that in other autistic spectrum disorders (e.g., Asperger’s syndrome) different patterns may be noted (Klin et al., 1995). In addition, the ability to generalize and broadly apply concepts may be much more limited in children with autism than other children (Tager-Flusberg, 1981; Schreibman and Lovaas, 1973). As for other aspects of development, programs have been implemented to maximize generalization of learning (Koegel et al., 1999), but this process cannot be assumed to occur naturally.

In autism research, IQ scores are generally required by the highest quality journals in descriptions of participants. These scores are important in characterizing samples and allowing independent investigators to replicate specific findings, given the wide variability of intelligence within the autism spectrum. IQ is associated with a number of other factors, including a child’s sex, the incidence of seizures, and the presence of other medical disorders, such as tuberous sclerosis. Several diagnostic measures for autism, including the Autism Diagnostic Interview-Revised, are less valid with children whose IQ scores are less than 35 than with children with higher IQs (Lord et al., 1994). Diagnostic instruments often involve quantifying behaviors that are not developing normally. This means that it is difficult to know if the frequency of autism is truly high in severely to profoundly mentally retarded individuals, or if the high scores on diagnostic instruments occur as the result of “floor” effects due to the general absence of more mature, organized behaviors (Nordin and Gillberg, 1996; Wing and Gould, 1979).

IQ scores have been used as outcome measures in several studies of treatment of young children with autism (Lovaas, 1993; Sheinkopf and



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