A directional bias for studies of laterality.

We have shown that a directional bias (D), previously thought to be unrelated to cerebral lateralization, is, in fact, intimately associated with it. In a group of fully consistent dextrals without familial sinistrality, the direction of lateral asymmetries depended upon the direction of D. Left-directed dextrals manifested the usual visual field advantages for linguistic and spatial material, while right-directed dextrals did not. D is therefore recommended as moderator variable for future studies of laterality.