Rehearsal in the visuospatial sketchpad : spatial sequence memory and central executive process

Within the framework of the working memory model (Baddeley and Hitch, 1974; Baddeley, 1986), numerous studies have explored the nature of verbal rehearsal and the phonological loop, but fewer have investigated rehearsal in the visuospatial sketchpad and this mechanism remains less well understood. Baddeley (1986) suggested that an implicit motor-based process might be implicated, and proposed a link between movement and visuospatial rehearsal. Evidence for this link was provided by Logie and Marchetti (1991) who found that spatial tapping disrupted memory for spatial sequences, while viewing irrelevant pictures disrupted recall for colour hues. These results confirmed a visual-spatial double dissociation in the visuospatial sketchpad, and subsequently Logie (1995) revised the model of the sketchpad to account for rehearsal by including a mechanism for storing visual information (visual cache) and an active spatially-based mechanism for rehearsal (inner scribe). This model has stimulated much research and although evidence supports the concept of a visual cache, the mechanism of the inner scribe is not well understood, largely due to its complexity. Therefore, the aim of this thesis was to explore the role of movement in visuospatial memory using Logie's (1995) reformulation of the visual spatial sketchpad as a conceptual framework. Three experiments using first year university students as participants were conducted. The first was an attempted replication of Logie and Marchetti (1991), chosen to confirm the selective effect of movement on spatial memory. Unexpectedly, the replication was unsuccessful with no visual-spatial dissociation demonstrated, but rather a generalised effect of interference. When a subset of poorer performing participants was excluded from analysis, the results moved in the expected direction, although the differences were still non-significant. Two further experiments were conducted specifically to examine spatial rehearsal processes. Experiment 2 compared spatial memory performance with a simple measure of memory span (digits forward) using an interference paradigm with three secondary interference tasks. It was found that although higher span participants performed significantly better than lower span participants, the expected interaction between span and interference type did not occur. Experiment 3 compared spatial memory with performance on the PASAT, a measure of divided attention containing storage and processing components. Again, high scoring PASAT participants performed significantly better than low scoring PASAT participants. Although the interaction was non-significant, results showed a trend for high PASAT participants to make fewer errors than low PASAT participants, with post-hoc analyses revealing that the high PASAT group made significantly fewer errors under the spatial interference condition. This finding suggests that individuals with more efficient attentional processes are better able to cope with dual task demands when rehearsing spatial information in working memory. The findings are discussed with reference to individual differences in working memory, problems with interpreting results within the conceptual framework of Logie's (1995) model, and issues concerning subject selection in working memory research.