Hemispheric dominance for mental rotation: it is a matter of time.

Mental rotation is often said to be a right-hemisphere function. The evidence for this claim, however, remains equivocal. To investigate whether right-hemispheric superiority relates to speed of processing, we measured the latencies and amplitudes of individual participant's mental-rotation event-related potential effects over the parietal electrodes. The results suggest that increases in parietal negativity begin around 400 ms after stimulus onset, and continue until 550 ms over the right hemisphere, and 610 ms over the left hemisphere. The effect of orientation on event-related potential amplitudes during those times do not differ between hemispheres. These results indicate that the lateralization effect is primarily related to timing, rather than the extent of cortical involvement.