Mothers' and fathers' lateral biases for holding their newborn infants: a study of images from the World Wide Web.

Photographic and direct-observation studies show that most adults hold infants on the left side. This basic directional effect is well established, but other details are still uncorroborated, uncertain, or inconsistent across studies. These include the overall strength of the bias, the role of the sex, parental status, and experience of the holder, and the sex and age of the infant. Given their importance for understanding the bias, we sought further information from a large sample of photographs of mothers and fathers, some of them first-time parents, others not, holding their infants in the first minutes, hours, or days after birth. The results confirmed the basic directional effect and provided information on the other variables. They also raise questions for further research, especially as it pertains to the use of photographs vs direct observation.