Mental rotation and simulation of a reaching and grasping manual movement.

This paper deals with the kind of manual movement subjects mentally simulate when solving a left-right judgment task that requires rotating images of hands. 50 female students were asked to judge the laterality of drawings of rotated hands presented successively to the right and left visual hemifields by clicking on a mouse using either the right or left hand. Reaction times and accuracy of judgment were recorded. Analysis showed performances varied with the rotation angle at which the stimulus was presented, indicating that the subjects mentally simulated a rotation process. An interaction occurred between the visually presented hand and the responding hand, which suggests that the mental rotation process involved the simulation of a hand movement. Performance improved when the drawing of a hand was presented in the 'palm-up' position, and to the visual hemifield opposite with respect to the hand the subject moved mentally. The latter two findings suggest that the subjects performed a simulated reaching and grasping movement rather than a simulated positioning movement.