APA Dictionary of Psychology

a disorder exemplified by difficulty in locating a specific number in a random array on a board as a result of a lesion in one cerebral hemisphere. Normally, individuals perform better when the number sought is to the left of the midline. Individuals with left-hemisphere damage also do better when the number is to the left of the midline, whereas those with right-hemisphere damage perform better when the number is to the right of the midline.