Doctor of Philosophy (Ph.D.)

This thesis investigated the visuo-spatial component of Baddeley and Hitch’s multi-component working memory model in 8- and 11-year-olds. Previous research with adults found that visuo-spatial short-term and working memory tasks impose similar demands on executive resources. This suggests the distinction between short-term and working memory is less well defined in the visuo-spatial domain than in the verbal domain. I examined the extent of executive involvement in the performance of visuo-spatial short-term and working memory tasks and whether this varied with age. A dual-task methodology was used; an executive suppression task, random number generation, and a control articulatory suppression task were paired with the visuospatial short-term and working memory tasks. All children performed the tasks in the single and dual task conditions. The first series of experiments examined the spatial subcomponent, and the second, the visual subcomponent. A reanalysis of the data was then conducted to directly evaluate the differences between the two subcomponents.

In Chapter 2, spatial short-term and working memory tasks (i.e., the Corsi Blocks task and Letter Rotation task respectively) along with an executive spatial visualisation task (Paper Folding task) as a control task, were administered to the children. In Chapter 3, a visual short-term memory task (Visual Patterns Test) and a visual working memory task (Patterns Memory task) were administered. The executive suppression task caused significantly impaired performances on all five visuo-spatial tasks in the dual task condition. In contrast, the articulatory suppression task only significantly impaired performance on the spatial working memory task and the visual short-term memory task. Chapter 4 found that the spatial short-term memory task engaged executive resources to a greater extent than the visual short-term memory task, while both working memory tasks were equally impaired by the executive suppression task. Articulatory suppression impaired performances on both working memory tasks and the visual short-term memory task, but did not impair performance on the spatial short-term memory task. However, the impairment was much smaller than that caused by executive suppression. The older children performed better on all tasks than the younger children as hypothesised, but their performance was more impaired by both suppression tasks than expected compared to the younger children regardless of subcomponent and memory type. There was also no age-related variation in the extent of executive requirement between the short-term and working memory tasks.

These results suggest that in the visuo-spatial domain, performances on both short-term and working memory tasks are dependent on executive resources. This demand is greater for the spatial subcomponent than for the visual subcomponent in the younger children. Visual short-term and spatial working memory tasks also seem to engage phonological resources to some extent. These findings are attributed to differences in employment of cognitive or mnemonic strategies. The older children were more likely than the younger children to employ strategies hence they engaged executive resources to a greater extent than the younger children. This thesis adds to the growing amount of evidence that the nature and structure of the visuo-spatial sketchpad is unlike that of the phonological loop.