Visuospatial working memory, movement control and executive demands.

Developments in the concept of a specialist visuospatial resource in working memory owe much to a pair of tasks originally developed by Brooks (1967), involving respectively the generation and retention of a mental image of a matrix pattern and the retention of a verbal sequence. Previous literature has demonstrated that the matrix task calls on cognitive resources which are involved in both the processing of visual input and the generation of movement sequences. Using dual task methodology, the study reported here demonstrates that the matrix and verbal versions of the task do indeed rely on separate, specialized cognitive resources, one of which is also involved in generation of action. However, when the secondary task (random generation of numbers) was very demanding of general purpose cognitive resources both the matrix and verbal tasks were performed poorly, suggesting that each of these tasks draw heavily on a common, general purpose resource as well as on their respective specialist resources. It is argued that random generation offers a means to assess general purpose cognitive resources and that the cognitive processes involved in the Brooks tasks may be more complex than has been previously assumed.