Eye movements and visuospatial problem solving: identifying separable phases of complex cognition.

Identifying overtly observable indicators of cognitive processes should provide a promising basis for a more precise tracking of the associated cognitive and neural events. In the current study we used recordings of eye movements to gain deeper insight into the time course of visuospatial problem solving as measured by the Tower of London. Single-trial, saccade-locked analyses revealed that, despite the complexity of the implemented task, gaze alternations between start and goal state followed a highly regular pattern. Consistent with the buildup of an internal representation, the first two fixations were of constant duration and unaffected by experimental variations of planning demands. Instead, planning manipulations exclusively influenced the duration of the very last fixation before problem execution. Our results demonstrate that different phases of complex cognition can be identified on a single-trial level using eye movement analyses.