Hemispheric specialization for mental rotation

A sample of 133 normal subjects, and one commissurotomized subject, were given a "mental-rotation" task, in which they were timed as they decided whether rotated letters, flashed in the left or right visual hemifield, were normal or backward. The normal subjects showed a significant right-hemifield advantage in reaction time, while the commissurotomized subject showed a pronounced left-hemifield advantage in both accuracy and reaction time. We argue that mental-rotation is primarily a right-hemispheric specialization, but that this was offset in the normal subjects by a stronger left-hemispheric specialization for letter identification.