Changes in lateral differentiation of head posture in the human neonate.

Developmental changes in the relationship between lateral differences in responsiveness and the assumption of asymmetrical head postures were examined. The head turning of 70 infants ranging in age from 0-72 hr was observed following a procedure (maintenance of the head in a midline position) known to reduce or eliminate lateral differences in the infant's response to stimulation. Even following this procedure infants older than 12 hr made significantly more right than left head turns whereas younger infants exhibited no such difference. When lateral differences in sensitivity were not interfered with in 0 to 12 hr old infants (n=20) they, kile the older infants, made significantly more right than left turns. These results are discussed in terms of possible developmental consequences of a reciprocity between asymmetric head position and lateral differences in sensitivity.