The inner working of dynamic visuo-spatial imagery as revealed by spontaneous eye movements

Mental imagery is a basic form of cognition central to activities such as problem-solving or creative thinking. However, phenomena like mental rotation, in which mental images undergo spatial transformations; and motion imagery, in which we imagine objects in motion, are very elusive. Although widely investigated, mental rotation in humans has never been observed directly in its instantaneous evolution. This chapter is aimed at showing that, as these processes give rise to organized patterns of eye movements; the underlying mental kinematics can be successfully recovered. In a visuo-spatial variant of mental rotation, sequences of saccades repeatedly and spontaneously reproduced the circular trajectory supposed to be mentally covered. The average gaze rotation had an ordered angular progression, with an asymmetrical angular velocity profile whose peak and mean velocity increased with the amount of rotation, as in goal-directed movements. In addition, spontaneous saccades during instructed rotary motion imagery revealed a considerable capability of the eyes to reproduce the imagined motion without introducing important distortions. Thus the recording of spontaneous eye movements can be a valuable tool to objectively measure the time-course of visuo-spatial dynamic thinking.