Planning Processes and Age in the Five-disc Tower of London Task

Abstract

This paper reports a study of planning processes in the five-disc Tower of London (TOL) task in 20 younger and 20 older adult participants. A concurrent direct “think-aloud” method was used to obtain data on planning processes prior to moving discs in the TOL. A check was made of the effects of verbalising by comparing performance data from the experimental groups with data from control groups who did not verbalise during planning or moving. Verbalising slowed down planning and moving but did not appear to distort the participants' approaches to the task. Older and younger participants did not differ in average moves taken to solve the tasks. However, older participants' planning was less complete and more error-prone than that of younger participants. The planning processes were characterised as showing a means-ends “goal selection” strategy. In this strategy participants (1) identify a single active goal disc at the start, (2) select moves and move sequences to enable the placing of the current goal disc in its target position, and (3) continue in this way until all discs are in their target positions. Age differences were found in the planning stage, during which there was no stimulus support and hence a substantial working memory load. During the move phase there was stimulus support and hence little loading of working memory. Age differences in moves required were not found in the move phase. As older participants tend to have depleted working memory capacity the present results suggest that working memory is heavily loaded in TOL planning but less so in the move phase of TOL.