Memory functioning in children and adolescents with autism.

Impairments in cognitive functioning are commonplace in neurodevelopmental disorders (Bishop, 2009), including disrupted memory functioning in autism (Ben Shalom, 2003; Frith & Hill, 2003). Kanner (1943) was the first to clinically describe fascinating memory profiles in individual children with autism, puzzling over why phenomenal ability in a specific type of memory was often combined with impairment in other aspects of memory in the same affected individual, and why impairments in memory and learning were so pervasive in autism. Even though memory impairments have been reported in autism, an autism-specific profile of dysfunctional memory has not been established (Minshew & Williams, 2007), but several theories have been proposed to explain the heterogeneity of cognitive impairments observed in autism. Most fall under the proposition that higher-level cognitive functions that require organization or strategy such as memory are affected, while more basic perceptual processes are left intact or even enhanced in some individuals with autism (Jeste, Friedman, & Urion, 2009; Mottron, Dawson, Soulieres, Hubert, & Burack, 2006). For example, Ben Shalom (2009) has recently suggested a 3-tiered model of cognitive functioning in autism, consisting of basic, integrative, and higher-order or “logical” levels of processing. Within a memory framework, the autism condition thus spares, or relatively spares, low-level perceptual and procedural information processing, while disabling the consolidation of higher-level or event-related information (i.e., episodic or autobiographical memory). Higher-level memory for context-independent facts (i.e., semantic memory), however, is thought to be either not affected or minimally affected and used to compensate for the lack of integrative episodic memory among high-functioning individuals. Similarly, others have suggested that the semantic or visual complexity and volume of information to be processed, integrated, and retained are key factors that define memory performance deficits in autism (Williams, Goldstein, & Minshew, 2006a, 2006b). Recent studies of memory in autism have focused on individual profiles from broadband neuropsychological batteries, which assess episodic memory functions through a variety of stimuli and task requirements, incorporating visual, verbal, list learning, associative, and working memory paradigms. Minshew and Goldstein (2001) administered a mixed clinical and experimental memory battery, investigating effects of stimulus complexity on memory performance among high-functioning adolescents and young adults with autism matched on verbal and performance IQ. They found that the autism group often performed equal to controls on verbal or visual tasks with low processing load. When evaluated using tasks with similar content but increased stimulus complexity, however, memory deficits relative to controls became increasingly apparent in the autism group. More recent studies of autism have reported on memory functioning in childhood, using standardized, commercially available test batteries. Lajiness-O’Neill et al. (2005) reported results using the Test of Memory and Learning (TOMAL; Reynolds & Bigler, 1994), which was administered to a size-limited sample of children with high-functioning autism (HFA). Participants were characterized by mean verbal reasoning scores in the borderline range, with performance IQ in the high average range. Analyses of memory scores indicated functioning in the low average range on composite TOMAL measures of overall, verbal, nonverbal, and delayed recall memory. In a separate study, Williams, Goldstein and Minshew (2006b) reported on memory functioning in childhood autism among a relatively large sample, in which HFA and controls were matched on both verbal and performance IQ. Using the Wide Range Assessment of Memory and Learning (WRAML, Sheslow & Adams, 1990), they found evidence for reduced memory performance across verbal and visual domains compared to the control sample, matched in intellectual ability. Consistent with prior research on the effects of stimulus complexity on memory performance, Williams and colleagues found that HFA and controls performed similarly on perceptually simple tasks, while complex task performance discriminated between the groups. The generalizability of the Williams et al. (2006b) findings of reduced memory performance in children with autism is unknown using other similarly standardized measures of memory function. Accordingly, the present investigation examined memory performance and provides descriptive neuropsychological test information in an autism sample of children and adolescents using the TOMAL. Given the past observations of reduced memory performance in autism compared to controls we expected to find that as a group the subjects with autism would exhibit reduced memory performance on the TOMAL. We anticipated a profile of generalized reduction in memory functions across TOMAL subtests. As aggregate measures, the TOMAL composite indices were expected to show greater group differences. Compared to the Williams et al. (2006b) study with the WRAML, the current investigation included a broader range of verbal intellectual ability and subjects were not matched on verbal intellectual ability but were statistically comparable on nonverbal intellectual ability. Because of the diagnostic requirement for having “qualitative impairments in communication” in autism, matching on verbal abilities runs the risk of overcontrolling for a core cognitive dimension of the disorder. Dennis et al. (2009) provide the rationale for why IQ does not necessarily need to be a matching variable or a statistical covariate in investigations of developmental disorders. Nonetheless, also recognizing the importance of examining how memory performance may differ between subjects with autism and controls with similar intellectual abilities, results are also presented for a subgroup that was matched for both verbal and nonverbal intellectual ability.