Early infant motor asymmetries and handedness: A critical evaluation of the evidence

Evidence relating to early infant motor asymmetries is critically evaluated with respect to (a) hand and arm movements, (b) head turning and the rooting reflex, (c) postural orientation, and (d) parental holding and carrying practices. The evidence suggests that where asymmetries occur, they may be temporary developments that reflect the cumulative pre‐ and/or postnatal experiences of the infant up to that time. Claims of early infant and other asymmetries predicting adult handedness are considered doubtful in view of the handedness criteria employed. Spontaneous fluctuations in both the absolute and relative activity of the right and left hands characteristic of infancy may also account for some of the otherwise incompatible findings reported previously. It is suggested that there is currently insufficient behavioral evidence to conclude that the cerebral lateralization of motor functions is based on a hemispheric specialization that is fixed at birth and is unchanging thereafter. Some possible lines for future research are indicated.