ABSTRACT
In the five-disc version of the TOL used in our studies, the task differs from the original design by Shallice (1982); not only are there more discs but the rods are identical in length. The procedure also used instructions to plan the whole sequence of moves that must be carried out mentally (the “plan phase”) before executing the planned sequence in a “move phase”. This methodology attempts to separate out the mental planning phase of the task from the subsequent motor execution of the plan, although in fact, people are unlikely to attempt a full mental plan of a long sequence of moves, and will tend to carry out plan completion, correction and modification on-line during the “move phase” (Phillips, Wynn, McPherson, & Gilhooly, 2001). The TOL is likely to make extensive demands on working memory, because efficient generation, execution and modification of a cognitive plan demand simultaneous storage and processing of numerous subgoals. There is evidence for the involvement of working memory in the TOL (Welsh, SatterleeCartmell, & Stine, 1999), particularly visuo-spatial working memory (Phillips, Wynn, Gilhooly, Della Sala, & Logie, 1999). Neuroimaging studies provide consistent evidence for the involvement of the frontal lobes, particularly dorsolateral prefrontal regions, in the TOL task (e.g., Baker et al., 1996; Owen, 1997; Owen, Doyon, Petrides, & Evans, 1996).
