The influence of lying positions and postural control on hand–mouth and hand–hand behaviors in 0–4-month-old infants

The purpose of this study was to verify how and when body position and postural control affect hand–mouth and hand–hand behaviors in infants during their first 4 months of life. Forty healthy infants were positioned in supine, prone and side-lying positions so that frequency and duration of the behaviors were quantified. Postural control when in supine and prone was also analyzed. The prone position elicited hand–mouth behavior in 0–2-month-old infants. The side-lying position elicited hand–mouth behavior in 3–4-month-old infants and hand–hand behavior in 2–4-month-olds. The increased postural control promoted the emergence of hand–hand behavior when in supine, and decreased hand–mouth behavior when in prone. The results show that self-exploratory behaviors may be affected not only by extrinsic constraints, represented by different body positions, but also by intrinsic constraints, represented by characteristic action possibilities and postural control of each age group.