A Comparative Study of Working Memory in Children with Neurodevelopmental Disorders

Background: Previous research has provided conflicting reports with regards to the functioning of the various components of working memory in children with neurodevelopmental disorders, and in particular in those with autism. This research was initiated to answer some of the questions raised by these research studies and to provide a comparison of performance of children with different neurodevelopmental disorders on the same measure of working memory. Aim: The purpose of this research was to investigate working memory functioning of children with neurodevelopmental disorders including autism spectrum disorder (ASD), intellectual disability (ID), and specific and language impairment (SLI). A group of typically developing (TD) children was also tested for comparison. The groups included in the present study were selected with the aim of identifying varying patterns or profiles of working memory dysfunction, as a function of the different levels of intellectual functioning within these neurodevelopmental groups. The scores of children with SLI were within the average range on the performance IQ scale (PIQ). Low functioning children with ASD have a Full scale IQ (FSIQ) score of less than 70; high functioning children with ASD have a Full Scale IQ score above 70. Children with ID have a FSIQ score of lower than 70. Within each group, there can be considerable variation in IQ score, allowing the examination of working memory as a function of IQ. The research also aimed to explore the relationship between intelligence and memory, with particular reference to crystallized and fluid intelligence and processing speed. The present research study also aimed to examine any particular working memory profiles that might characterise each group; these were predicted to vary across groups. The hypotheses were generated based on previous research in this field, which suggests that children with neurodevelopmental difficulties demonstrate impairments in memory functioning, particularly affecting working memory, compared to typically developing children. Method: Data were collected from children in pre-schools and schools located in the Munster region of the Republic of Ireland. In total, 96 children participated, with ages ranging from 48 to 192 months. The ASD group consisted of 26 children (23 male; 3 female) with an age range of 49-161 months. The group with ID consisted of 32 children (21 male; 11 female), with an age range of 56-192 months. The SLI group consisted of 15 children (10 male and 5 female) with an age range of 75-154 months. The typically developing children consisted of 23 children (12 male and 11 female) with an age range of 48-190 months. The SLI group had a lower age range when compared to the other three groups; however, this would not have had any substantial effect on the outcome of the results as the test batteries used in the research were age normed. The children were assessed using the Wechsler Intelligence Scale for Children-IV (WISC-IV) or the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III), as appropriate for their age, to determine their level of intellectual ability. The children with a diagnosis of ASD and SLI were assessed by the relevant professionals to confirm their diagnosis. All children were subsequently assessed using a measure of the components of working memory, the Automated Working Memory Assessment (AWMA), in order to identify any relative strengths and weaknesses in their working memory functioning. Results: The results indicate that the high functioning children with ASD performed equally well on almost all the subtests of AWMA when matched with the typically developing children on IQ and age. There was no difference observed on the memory tasks between the performance of low functioning children with ASD and those with ID. The children with ID performed poorly on the memory tasks compared to the children with average intelligence. The SLI group showed impairment on the verbal memory measures and, when IQ was controlled, the SLI group indicated some further impairment on visual spatial tasks when their performance was compared with the typically developing children. Furthermore, these groups presented their own unique profiles when Verbal Comprehension Index (VCI), Perceptual Reasoning Index (PRI) and Processing Speed Index (PSI), measures that contribute towards calculating the Full Scale IQ (FSIQ), were statistically controlled. The VCI and PRI are considered to measure crystallized and fluid aspects of intelligence respectively. Correlational analyses indicated a unique profile for each group. Conclusion: The implications of the findings are discussed with reference to relevant research and interventions for children with neurodevelopmental difficulties. The present research highlights the differential performance of the four groups with respect to working memory, and notes the contribution of intellectual functioning to the memory dysfunction