| Inconclusive results have been found when examining age-related differences within visual-spatial working memory (Salthouse, 1987; Salthouse, Babcock, & Shaw, 1991; Salthouse & Mitchell, 1989). Of interest is whether the visual-spatial sketchpad and/or the central executive drive age-differences. One difficulty in assessing age-related differences stems from ineffective or weak task manipulations that do not impose load changes clearly within each stage. Another problem is related to the bi-directional linkage between the visual-spatial sketchpad and the central executive, which makes assessing each stage separately more difficult. To address these issues, the current study used a newly developed measure of visual-spatial working memory, which incorporated several specific task manipulations. In order to assess the full continuum of maintenance and processing resources, multiple measures of accuracy and reaction time were used. Participants were given a series of animals, varying in number and size, and were required to arrange them from largest to smallest or from smallest to largest. The number of to-be-remembered animals (3 or 4) was aimed at imposing maintenance load changes. Discrimination difficulty (easy or hard) and arrangement order (correct, reversed, or scrambled) were aimed at imposing processing load changes. Thirty-two younger adults and 25 older adults completed the experimental task and several additional measures including: marker tasks of visual-spatial working memory, speed of processing, and crystallized intelligence. Strong support was found for the effectiveness of the selected task manipulations, stimulus set length, discrimination difficulty, and arrangement order. Age-related differences were found for both maintenance resources and processing resources, suggesting the visual-spatial sketchpad and central executive are involved, respectively. Support for over-lap between the maintenance and processing stages was also found, suggesting when resources are limited both stages become over-taxed, affecting performance. Interestingly, speed of processing did not completely mediate the relationship between task performance and age, suggesting other variables may be important in understanding age differences within visual-spatial working memory. These findings suggest it is important to develop effective task manipulations that more clearly impose maintenance and processing resources. Additionally, using multiple measures to assess maintenance and processing resources seems beneficial in understanding the bi-directional linkage and age-related changes in visual-spatial working memory. |
