The strategic control of gaze direction in the tower of London task

In this paper, we describe a novel approach to the study of problem solving involving the detailed analysis of natural scanning eve movements during t he "one-touch" Tower-of-London (TOL) task. We showed subjects a series of p ictures depicting two arrangements of colored balls in pockets within the u pper and lower halves of a computer display. The task was to plan (but not to execute) the shortest movement sequence required to rearrange the balls in one half of the display (the Workspace) to match the arrangement in the opposite half (the Goalspace) and indicate the minimum number of moves requ ired for problem solution. We report that subjects are more likely to look towards the Goalspace in the initial period after picture presentation, bur bias gaze towards the Workspace during the middle of trials. Towards the e nd of a trial, subjects are once again more likely to fixate the Goalspace. This pattern is found regardless of whether the subjects solve problems by rearranging the balls in the lower or upper visual fields, demonstrating t hat this strategy correlates with discrete phases in problem solving. A sec ond experiment showed that efficient planners direct their gaze selectively towards the problem critical balls in the Workspace. In contrast, individu als who make errors spend more rime looking at irrelevant items and are str ongly influenced by the movement strategy needed to solve the preceding pro blem. We conclude that efficient solution of the TOL requires the capacity to generate and flexibly shift between control sets, including those underl ying ocular scanning. The role of working memory and the prefrontal cerebra l cortex in the task are discussed.