Hey Good-Lookin': About Newborns Recognizing Their Mothers

I recognized a friend at a restaurant last night. We walked quickly toward each other, hugged, called each other by name, and began to dish the gossip. Other people watching (if any) would have agreed-- yes, they recognized each other.

But, of course, people who say newborn babies recognize their mothers don’t mean they do any of those grown-up things. I want to take some space here to talk about exactly what they do mean.

The first issue is what things babies can do that could let us tell whether they recognize someone. Their hearing is quite good, normally. Even before they’re born they show that they have heard something by sudden movements. After they’re born, they can choose a sound to listen to if we give them an artificial nipple rigged so their sucking can trigger one sound or another. Their vision is not as good as their hearing at birth-- detail vision is not what it will later be, and the clearest images they get are of objects about 12 to 18 inches from the eyes. They have some preferences for what they look at, and show those by looking longer at certain things, especially faces. They have excellent capacities for smell and taste, too, but those are much more difficult to work with because a particular smell or taste may linger for quite a while and is not so easy to change.

Newborns have another highly relevant ability: they are able to habituate and dishabituate to a sensory stimulus. This is a cognitive skill that may be the foundation of all other thinking. Basically, a baby habituates when he or she stops looking at or paying attention to a sight or sound that has been going on for a while. Dishabituation occurs when a new stimulus replaces the old one and the baby begins to look and pay attention once again. Young babies are much interested by novelty and on the whole pay more attention to unfamiliar than to familiar things-- a much different situation than we see in older children or adults, who like to examine familiar things very closely.

Habituation seems to apply to all senses and begins very early in life. For example, in one study, preterm babies held unfamiliar shapes in their hands longer than they did familiar ones (Lejeune, F. et al., [2010], The manual habituation and discrimination of shapes in preterm human infants from 33 to 34+6 post-conceptional age. PLoS ONE, Vol. 5, 1-7). And when it comes to measuring recognition, habituation is a real complicating factor, as ordinarily very young babies show more interest in unfamiliar things and less in familiar things, raising the possibility that “recognition” might be defined as ignoring something rather than paying attention to it. Nevertheless, studying habituation lets us see whether a baby responds differently to two faces or voices, and differences in response are enough to let us know whether there is recognition.... but not all research takes habituation into account or uses it as a way to understand the baby's reactions.

In one study, babies 2-4 days old showed different movements in response to their mothers’ voices and strangers’ voices, and also to their mothers’ voices speaking in an adult-directed way versus their mothers speaking “motherese” with its high pitch and exaggerated intonations. But when similar recordings were made of unborn babies (about 36 weeks gestational age) as they listened to their mothers’ or strangers’ voices from a speaker placed on the mothers’ abdomens, the babies did not react differently to mothers and strangers; on the other hand, they did react differently to the mother’s voice through the speaker and the mother’s voice when she was actually talking (Hepper, P.G., & Shahidullah, S. [1993]. Newborn and fetal rersponse to mother’s voice. Journal of Reproductive and Infant Psychology, Vol. 11, 147-153).

Anthony DeCasper is a researcher well-known for his 1986 work on recognition of mother’s voice and even of the “Dr. Seuss” story she read to her belly toward the end of pregnancy. He has continued to explore this topic and has found, not too surprisingly, that it’s all more complicated than it would appear. For example, in a recent study (Decasper, A.J., & Prescott, P. [2009]. Lateralized processes constrain auditory reinforcement in human newborns. Hearing research, Vol. 255, 135-141), he showed that the baby’s response to different sounds depends on which ear is being used, and therefore on which hemisphere of the brain is receiving messages about the sound. DeCasper provided the babies with a sucking device that could detect and record how fast the baby sucked. Faster sucking could produce one sound for the baby to hear, slower sucking a different sound. The sounds included an unfamiliar voice speaking, a recording of what the mother’s heartbeats sound like inside the uterus, and the mother’s voice speaking in either her native language or a different language.

Here are the complicated findings: When the baby had a choice between a stranger’s voice and the heartbeat, it chose the stranger’s voice only when listening with the right ear (through an earphone). It chose the heartbeats only when listening with the left ear. When the choice was between the mother’s voice and a stranger’s voice, or between the mother speaking her native language and speaking a foreign language, the baby chose the more familiar sound only when listening with the left ear. These findings suggest that when the baby is listening with both ears-- in its ordinary non-laboratory situation-- familiarity alone will not govern his or her attention and behavior. “Recognizing” does not seem to be such a simple matter.

Finally, I want to talk about a study that used habituation as part of its measure of babies’ looking preferences and ability to “recognize” (Figueiredo, B., et al. [2010]. Mother’s anxiety and depression during the third pregnancy trimester and neonate’s mother versus stranger’s face/voice visual preference. Early Human Development, Vol.86, 479-485). This study recorded how long a baby looked directly at its mother, who had spoken, as opposed to how long it looked at a stranger, who also spoke. (They were not present or speaking at the same time.) At the beginning of the study, the babies looked at the mothers for an average of 9.7 seconds, and at the strangers for an average of 6.8 seconds. When tested again a bit later, after habituation had taken place, they looked at the mothers for an average of 6.1 seconds and at the strangers (a different stranger than the one originally used was brought in for this) for 9 seconds. This suggests that they were socially competent enough to tell the difference between the mother and the stranger, but they had no overwhelming need to be attentive to the mother. Their recognition could be shown by the fact that they looked less at the mother rather than more.

A second, very interesting part of this study compared the behavior of babies whose mothers were anxious or depressed during pregnancy with that of those who were not. Newborns of depressed or anxious mothers showed much less “recognition” in the form of different amounts of looking toward their mothers and toward strangers. The impact of those differences on maternal attitudes and on the development of relationships may be a matter of concern, and suggests an emphasis on the transactional nature of development, in which mothers and babies influence each other in ways that change with time and experience.