Susceptibility to interference effects in short-term memory of normal and retarded readers

Disentangling Processing and Storage Accounts of Working Memory Development in Childhood

Researchers have been asking the question of what drives the development of working memory (WM) during childhood for decades. This question is particularly challenging because so many aspects of cognition develop with age that it is difficult to disentangle them and find out which factors are causal or fundamental. In this review, we first prepare to discuss this issue by inquiring whether increases in storage, processing, or both are the fundamental driving factor(s) of the age-related increase in WM capability in childhood. We contend that by experimentally manipulating either factor and observing changes in the other, it is possible to learn about causal roles in WM development. We discuss research on school-aged children that seems to suggest, by means of such an approach, that the growth of storage is causal for some phases or steps in WM tasks, but that the growth of processing is causal for other steps. In our theoretical proposal, storage capacity of the focus of attention determines earlier steps of information processing by constraining the selective encoding of information into WM, whereas processing dependent on the focus of attention determines later steps, like the detection of patterns that can simplify the effective memory load and adoption of a proactive stance of maintenance in dual-task settings. Future directions for research are discussed.

Proactive interference and the development of working memory

Working memory (WM), the ability to maintain information in service to a task, is characterized by its limited capacity. Several influential models attribute this limitation in a large extent to proactive interference (PI), the phenomenon that previously encoded, now-irrelevant information competes with relevant information. Here, we look back at the adult PI literature, spanning over 60 years, as well as recent results linking the ability to cope with PI to WM capacity. In early development, WM capacity is even more limited, yet an accounting for the role of PI has been lacking. Our Focus Article aims to address this through an integrative account: since PI resolution is mediated by networks involving the frontal cortex (particularly, the left inferior frontal gyrus) and the posterior parietal cortex, and since children have protracted development and less recruitment of these areas, the increase in the ability to cope with PI is a major factor underlying the increase in WM capacity in early development. Given this, we suggest that future research should focus on mechanistic studies of PI resolution in children. Finally, we note a crucial methodological implication: typical WM paradigms repeat stimuli from trial-to-trial, facilitating, inadvertently, PI and reducing performance; we may be fundamentally underestimating children's WM capacity. This article is categorized under: Psychology > Memory Neuroscience > Cognition Neuroscience > Development.

Learning Linear Spatial-Numeric Associations Improves Accuracy of Memory for Numbers

Memory for numbers improves with age and experience. One potential source of improvement is a logarithmic-to-linear shift in children’s representations of magnitude. To test this, Kindergartners and second graders estimated the location of numbers on number lines and recalled numbers presented in vignettes (Study 1). Accuracy at number-line estimation predicted memory accuracy on a numerical recall task after controlling for the effect of age and ability to approximately order magnitudes (mapper status). To test more directly whether linear numeric magnitude representations caused improvements in memory, half of children were given feedback on their number-line estimates (Study 2). As expected, learning linear representations was again linked to memory for numerical information even after controlling for age and mapper status. These results suggest that linear representations of numerical magnitude may be a causal factor in development of numeric recall accuracy.

Auditory temporal processing deficits in children with reading disabilities

The role of central auditory processing in reading skill development and reading disorders is unclear. The purpose of this study was to examine whether individuals with specific reading disabilities (SRD) have deficits in processing rapidly presented, serially ordered non-speech auditory signals. To this end, we compared 12 children with SRD and 12 children without SRD on their ability to detect differences and similarities in pure tones of 1000 and 2000 Hz when these signals were presented in pairs (same or different tones, randomly ordered) with short (50 ms) versus long (500 ms) inter-stimulus intervals (ISI). Results showed that the children with SRD had significant difficulty in discriminating between pure tones with short, but not long ISI, whereas the controls performed well with both short and long ISI. The two groups did not differ significantly on measures of attention (d2) and performance IQ, and there were no significant correlations between these measures and ISI performance. There were significant correlations between the short ISI performance and phonologic awareness test results when the two groups were combined. These findings support the specific rapid auditory processing deficit hypothesis of SRD. Examination of intra-subject variability in performance indicated that children from the SRD group showed both decrement in performance with time on task and high overall variability in performance as compared to the controls. These findings underpin the importance of using time-series analyses of performance.

The development of memory and processing capacity

The assumption of some developmental theories that short-term memory is the workspace of higher cognitive processes, and consequently that span measures processing capacity, is claimed to be inconsistent with the working memory literature. 4 experiments, using children aged 5 to 12 years, contrast this theory with a model in which short-term memory and the processing space component of working memory are at least partly distinct. Experiments 1 and 2 varied processing load, holding duration constant. The processing load manipulation had little effect on recall of a short-term memory preload. Experiments 3 and 4 failed to support the prediction that the greater processing efficiency of older children would be associated with slower loss of information from short-term memory. Although counting and rehearsal rates increased with age, and correlated with span, they did not predict the rate of loss of memory preload due to intervening counting. The data suggest that effects obtained with short-term memory span do not provide clear indications of overall working memory development, because short-term memory span and the processing space component of working memory entail distinct systems.

The search for subtypes of specific reading disability: Reflections from a cognitive perspective

An overview of the literature on developmental dyslexia is offered, moving historically from attempts to identify a single underlying deficit to more recent efforts to define different subtypes of this developmental disorder. Two approaches to the subtyping problem are illustrated and briefly discussed. It is suggested that many of the remaining questions in dyslexia research could be more profitably addressed within the context of a coherent model of reading behaviour. In the latter half of this review, the potential implications of some aspects of the interactive reading theories for the study of reading dysfunction are explored.

Mediation or production deficiency in disabled readers

Deficiences in disabled readers' short-term memory processing were studied. A deficit in memory capacity versus susceptibility to interference was investigated by examining performance over trials. A mediation versus production deficiency in memory processing was examined by testing the effect of instructions for rehearsal on performance of average and disabled readers in Grades 2 and 5. Contrary to prior research, facilitative effects of rehearsal graders' memory was adversely affected by overt rehearsal. Requiring children to rehearse overtly at a set rate may account for the results. A second study examined effects of covert rehearsal on the memory of average and disabled readers in Grade 2 over trials. Facilitative effects of covert rehearsal were shown when data of children who spontaneously rehearsed were removed. A deficiency in production by second graders was supported. Disabled readers who did not rehearse were more susceptible to interference.

Mediation or Production Deficiency in Disabled Readers?

Deficiencies in disabled readers’ short-term memory processing were studied. A deficit in memory capacity versus susceptibility to interference was investigated by examining performance over trials. A mediation versus production deficiency in memory processing was examined by testing the effect of instructions for rehearsal on performance of average and disabled readers in Grades 2 and 5. Contrary to prior research, facilitative effects of rehearsal instructions on second graders’ memory were found only on Trial 1. Fifth graders’ memory was adversely affected by overt rehearsal. Requiring children to rehearse overtly at a set rate may account for the results. A second study examined effects of covert rehearsal on the memory of average and disabled readers in Grade 2 over trials. Facilitative effects of covert rehearsal were shown when data of children who spontaneously rehearsed were removed. A deficiency in production by second graders was supported. Disabled readers who did not rehearse were more susceptible to interference.