Dissociation between physical and mental number line bisection in right hemisphere brain damage.

To compare numeric quantities, humans make use of a 'mental number line' with smaller quantities located to the left of larger ones; it is unclear, however, whether orienting along the number line is like orienting along a physical line. We found that in brain-damaged subjects with defective leftward orienting, rightward deviation in the bisection of numeric and physical intervals is doubly dissociated. Deviation in numeric interval bisection was associated with prefrontal damage and spatial working memory deficit.