Right-handedness: a consequence of infant supine headorientation preference

Most newborn infants (65 percent) preferred to lie with their heads turned to the right, whereas 15 percent showed a distinct preference for the left. Orientation preference is maintained for at least 2 months and predicts preferential hand use in reaching tasks at both 16 and 22 weeks. Right head-orientation preference in early infancy may contribute to the early development of right- handedness. Article: Right- and left-handedness are associated with individual differences in a wide variety of psychological phenomena from cognitive styles to recovery of function after brain damage (1), but the causes of these associations are unknown. Studying the development of hand preference may disclose some causes of these functional associations. The two characteristics to be explained in human handedness are individual variability, which is common to humans and other mammalian species, and the predominance of right-handedness, which is unique to humans. In nonhuman species, limb preference is randomly distributed among right-, mixed-, and left-limb use (2). Although individual variability could be genetic in origin, the evidence from breeding studies in mice and ontogenetic studies of monkeys favors a nongenetic origin (3). Collins reported that mice reared under conditions favoring the use of the right limb develop a right-limb preference, whereas mice reared unde