Right-hand preference facilitated by rightward turning biases during infancy

A rightward turning bias is the earliest human asymmetry and may be a precursor of handedness. Head-turning affects arm position as part of the Asymmetric Tonic Neck Reflex (ATNR). The hypothesis was tested that turning biases operate in coordination with the ATNR to promote handedness by measuring reflex behavior during turns in the preferred vs nonpreferred direction. Twenty infants were filmed during spontaneous movement and during the following factorial design: head turned left vs right; voluntarily vs passively; 30 degrees vs 70 degrees. The incidence, strength, and duration of the ATNR were least when the child turned toward his/her preferred side. When right-preference children turned rightward, the occurrence of the ATNR was no better than chance. Thus, a child can orient toward the right hand with minimal intrusion of the ATNR upon limb position, perhaps promoting right-handedness.