AN ELECTROPHYSIOLOGICAL STUDY OF THE MENTAL ROTATION OF POLYGONS

REACTION times and event-related potentials (ERPs) were recorded durin g a task requiring subjects to decide whether two sequentially present ed polygons had the same shape regardless of differences in orientatio n. Reaction times increased approximately linearly with angular depart ure from upright orientation, which suggests that mental rotation was involved in the comparison process. The ERPs showed, between 665 and 1 055 ms, a late posterior negativity also increasing with angular dispa rity from upright, which we assumed to reflect mental rotation. Two ot her activities were exhibited, from 265 to 665 ms, which may be relate d either to an evaluation of the stimulus or a predetermination of its orientation, and from 1055 to 1600 ms attributed to the decision proc ess.