Effect of degree and direction of rotation in egocentric mental rotation of hand: an event-related potential study.

We explored the neural mechanisms of mental rotation of hand, which may invoke a mental transformation of viewer's own hands. It was found that, when a hand picture was presented at an orientation rotated from the upright orientation, participants' performance in making left or right hand judgment was affected by the degree and direction of rotation, with the direction effect being implicated as the evidence for egocentric mental rotation. Our event-related potentials measure supported the idea that amplitude modulation in the parietal cortex is a psychophysiological marker of the mental rotation of hand. Furthermore, the rotation-direction-dependent modulation of a positive wave was identified as possible neural correlate for the egocentric nature of such mental rotation.