Investigations of working memory in adults indicates a modular system consisting of phonological and visuo-spatial subsystems coordinated by an attentional ‘executive’. Neuropsychological evidence supports this model in showing that components of working memory can be selectively impaired. The phonological subsystem is modelled as a time-based ‘phonological loop’ which is accessed directly by spoken inputs and indirectly by recoding visual inputs. Developmental studies of short-term memory for spoken items show that the phonological loop has similar characteristics over a wide age-span, and suggest that increased speed of subvocal rehearsal is an important factor in developmental change.

Correlational data suggest that the phonological loop plays a significant role in vocabulary learning. In contrast, developmental studies of short-term memory for visual stimuli suggest that younger children rely on visuo-spatial working memory, whereas older children switch to using the phonological loop. Reasons for this transition are unclear, especially as verbal recoding is not always helpful, e.g. it can hinder performance of visual imagery tasks. Developmental changes in ‘complex span’ tasks like counting span, reading span and operation span have been interpreted in terms of a resource-sharing model of executive capacity. However, recent experiments suggest that complex spans are insensitive to processing ‘load’ but are influenced by the time over which stored information loses activation, favouring an alternative ‘task-switching’ model of executive function. Developmental changes in complex spans show a continuous relationship with speed of processing, consistent with task-switching. Spans also predict children’s scholastic attainment in areas such as reading and arithmetic. Overall, evidence suggests that development of working memory involves continuous changes in its components but a marked qualititative change in access. Strong relationships between subsystems and cognitive skills are consistent with the assumption that working memory plays an important but diverse role in cognitive development.

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