Christopher Jarrold

The complexities of complex span: explaining individual differences in working memory in children and adults

Two studies are presented that investigated the constraints underlying working memory performance in children and adults. In each case, independent measures of processing efficiency and storage capacity are assessed to determine their relative importance in predicting performance on complex span tasks,which measure working memory capacity. Results show that complex span performance was independently constrained by individual differences in domain-general processing efficiency and domain-specific storage capacity. Residual variance, which may reflect the ability to coordinate storage and processing, also predicted academic achievement. These results challenge the view that complex span taps a limited-capacity resource pool shared between processing and storage operations. Rather, they are consistent with a multiple-component model in which separate resource pools support the processing and storage functions of working memory.

Genetically dissociated components of working memory: evidence from Down's and Williams syndrome

Wang and Bellugi [J clin exp Neuropsychol 1994;16:317 22] have suggested that Downs and Williams syndrome might be associated with specific and contrasting working memory deficits; with impaired verbal short-term memory in Downs syndrome, and a visuo-spatial short-term memory deficit in Williams syndrome. In two studies we examine whether these apparent deficits might simply be a consequence of the general pattern of learning difficulties associated with these disorders. Experiment 1 compared verbal and visuo-spatial short-term memory abilities in these groups, using analysis of covariance to control for mental age differences. In Experiment 2 individuals with Williams syndrome were matched to control groups for non-verbal mental age, and the short-term memory abilities of these matched groups were compared. The results of both experiments are broadly consistent with those reported by Wang and Bellugi, and support the view that working memory can be dissociated into separate subsystems.

Short-term Memory for Verbal and Visuospatial Information in Down’s Syndrome

Short-term memory for verbal and visuospatial information was examined in a group of children and teenagers with Downs syndrome. Performance on the verbal task was impaired relative to matched control groups, but there were no group differences on the visuospatial task. Relatedly, the Downs syndrome group showed inferior short-term memory for verbal as opposed to visuospatial information, whereas controls showed the opposite pattern. These findings did not appear to result from a general superiority of nonverbal abilities in the Downs syndrome group, or from hearing difficulties that might have impacted on the verbal short-term memory task, in which material was presented auditorily. The results are consistent with the suggestion that Downs syndrome is associated with a selective impairment of the phonological loop component of Baddeley and Hitchs (1974) working memory model.

Verbal Short‐term Memory Deficits in Down Syndrome: A Consequence of Problems in Rehearsal?

Individuals with Down syndrome suffer from relatively poor verbal short-term memory. Previous explanations of this deficit have been framed in terms of inefficient or absent rehearsal of verbal material in Down syndrome within the phonological loop component of Baddeley and Hitchs (1974) working memory model. Two experiments are presented which test this explanation by looking for the markers of rehearsal in children with Down syndrome and verbal mental age matched controls. Both experiments confirm that individuals with Down syndrome show poorer verbal short-term memory performance than controls. However, they rule out rehearsal as an explanation of these deficits because the evidence suggests that neither individuals with Down syndrome nor matched controls are engaging in spontaneous subvocal rehearsal. Other explanations of poor verbal short-term memory performance in Down syndrome, in terms of impairments both within and outside of the phonological loop system, are discussed. Practical implications for intervention strategies aimed at improving verbal short-term memory skills in Down syndrome are also outlined.

Mapping the Developmental Constraints on Working Memory Span Performance.

This study investigated the constraints underlying developmental improvements in complex working memory span performance among 120 children of between 6 and 10 years of age. Independent measures of processing efficiency, storage capacity, rehearsal speed, and basic speed of processing were assessed to determine their contribution to age-related variance in complex span. Results showed that developmental improvements in complex span were driven by 2 age-related but separable factors: 1 associated with general speed of processing and 1 associated with storage ability. In addition, there was an age-related contribution shared between working memory, processing speed, and storage ability that was important for higher level cognition. These results pose a challenge for models of complex span performance that emphasize the importance of processing speed alone.

A Review of Research into Pretend Play in Autism

Autism is currently diagnosed, in part at least, on the basis of problems in imagination. The article reviews the empirical evidence of difficulties in pretend play in autism, and focuses in particular on individuals’ ability to engage in pretence in free play conditions, to produce pretence in more structured situations, and to make sense of pretend actions carried out by another person. These data suggest that individuals with autism have a marked difficulty in producing pretend play, but one that is reduced by providing substantial structure to the play situation or by testing comprehension of pretence. The implications of these findings for theories of pretend play in autism, in terms of an inability to conceive of non-literal situations, a difficulty in imposing a pretend usage on an object, or a failure to gain a benefit from engaging in pretend play, are discussed.

Memory for actions in children with autism: self versus other

In order to ask whether autism is associated with difficulty in self-monitoring we gave a group of children and adolescents with autism a task in which they themselves had to remember whether they or another person had performed certain actions. In our first experiment, three groups of participants had to recall whether placements of picture cards had been made by themselves or by the experimenter. The participants with autism performed at a much lower level than the two comparison groups and, unlike the comparison groups, were not better at recalling their own placements. A second experiment tested the prediction arising from the monitoring-deficit account that the children with autism would be unimpaired when the placement of the items did not alternate between self and other. This prediction was confirmed moderately well. Additionally, in contrast to that of the comparison groups, the performance of the participants with autism was unaffected by whether self or other displaced the items. This is consistent with the existence of a monitoring deficit.

Language Profiles in Children with Autism: Theoretical and Methodological Implications

The profile of language abilities in autism was examined by giving a number of standardized language assessments to a group of 1 20 children with autism. These assessments included measures of comprehension and of production of both vocabulary and grammar. Contrary to initial predictions, the group performed at a similar level across the range of tests, showing a relatively uniform profile of language attainment. In addition, there was no evidence of different language profiles in any diagnostic subgroup of children, such as children diagnosed as having Asperger syndrome. The theoretical implications of these findings, and their practical implications for research methodology, are discussed.

Block Design Performance in the Williams Syndrome Phenotype: A Problem with Mental Imagery?

Williams syndrome (WS) is a rare genetic disorder which, among other characteristics, has a distinctive cognitive profile. Nonverbal abilities are generally poor in relation to verbal abilities, but also show varying levels of ability in relation to each other. Performance on block construction tasks represents arguably the weakest nonverbal ability in WS. In this study we examined two requirements of block construction tasks in 21 individuals with WS and 21 typically developing (TD) control individuals. The Squares tasks, a novel two-dimensional block construction task, manipulated patterns by segmentation and perceptual cohesiveness to investigate the first factor, processing preference (local or global), and by obliqueness to examine the second factor, the ability to use mental imagery. These two factors were investigated directly by the Childrens Embeded Figures Test (CEFT; Witkin, Oltman, Raskin, & Karp, 1971) and a mental rotation task respectively. Results showed that individuals with WS did not differ from the TD group in their processing style. However, the ability to use mental imagery was significantly poorer in the WS group than the TD group. This suggests that weak performance on the block construction tasks in WS may relate to an inability to use mental imagery.

Divided attention, selective attention and drawing: Processing preferences in Williams syndrome are dependent on the task administered

The visuo-spatial abilities of individuals with Williams syndrome (WS) have consistently been shown to be generally weak. These poor visuo-spatial abilities have been ascribed to a local processing bias by some [R. Rossen, E.S. Klima, U. Bellugi, A. Bihrle, W. Jones, Interaction between language and cognition: evidence from Williams syndrome, in: J. Beitchman, N. Cohen, M. Konstantareas, R. Tannock (Eds.), Language, Learning and Behaviour disorders: Developmental, Behavioural and Clinical Perspectives, Cambridge University Press, New York, 1996, pp. 367-392] and conversely, to a global processing bias by others [Psychol. Sci. 10 (1999) 453]. In this study, two identification versions and one drawing version of the Navon hierarchical processing task, a non-verbal task, were employed to investigate this apparent contradiction. The two identification tasks were administered to 21 individuals with WS, 21 typically developing individuals, matched by non-verbal ability, and 21 adult participants matched to the WS group by mean chronological age (CA). The third, drawing task was administered to the WS group and the typically developing (TD) controls only. It was hypothesised that the WS group would show differential processing biases depending on the type of processing the task was measuring. Results from two identification versions of the Navon task measuring divided and selective attention showed that the WS group experienced equal interference from global to local as from local to global levels, and did not show an advantage of one level over another. This pattern of performance was broadly comparable to that of the control groups. The third task, a drawing version of the Navon task, revealed that individuals with WS were significantly better at drawing the local form in comparison to the global figure, whereas the typically developing control group did not show a bias towards either level. In summary, this study demonstrates that individuals with WS do not have a local or a global processing bias when asked to identify stimuli, but do show a local bias in their drawing abilities. This contrast may explain the apparently contrasting findings from previous studies.