When depressed mothers talk to their babies, their speech lacks many of the familiar characteristics of "baby talk" and may consequently hamper their children's ability to learn language and other skills.
Researchers have found a significant difference in associative learning between infants who listened to voice samples from women who were depressed and women who were not.
"We found that depressed mothers who were trying to interest their infants in a toy - a stuffed gorilla - said the word 'gorilla' in a voice with relatively flat pitch. This raised the possibility that infants, who are known to react more strongly to speech high in pitch modulation, would not learn well about the world around them when prompted with speech uttered by depressed caregivers," said Peter S. Kaplan, a professor of psychology at the University of Colorado at Denver. This may help to explain why older children of depressed mothers frequently perform more poorly than other children on standard tests of child development.
Kaplan, along with Jo-Anne Bachorowski of Vanderbilt University and Patricia Zarlengo-Strouse of the University of Colorado at Denver, reported their findings in the current issue of Child Development.
In their study of 225 four month olds, the researchers examined "associative learning, a basic and ubiquitous form of learning in infants." During a series of trials, the infants heard a woman say, "Pet the gorilla," and then saw a smiling woman's face. Later, to test if infants had learned to associate the voice and face, the researchers tracked how much time infants spent looking at a newly introduced checkerboard pattern while the voice played.
Infants who heard women with low or moderate symptoms of depression spent significantly more time observing the checkerboard pattern compared with those who listened to severely depressed women. Prior research had shown that when the voice had not predicted the appearance of the face, it did not increase interest in the checkerboard pattern. The researchers also analyzed the characteristics of the women's voices. Less depressed women tended to change the pitch of their voice over a greater range compared with depressed women, who used a relatively more monotone delivery.
The researchers speculate that these pitch changes and other elements of baby talk serve to "increase the infant's state of arousal and, while in that state, infants ... process information more efficiently or completely." When depressed women speak to babies, however, their voices lack "the acoustic qualities [necessary] to sensitize infants," they say.
Previous research has shown that two and three-year-old children do better learning language when it is presented with the pitch changes and simplified grammar of baby talk rather than typical adult speech. Dr Kaplan and his colleagues suggest that depressed mothers may offer their infants relatively poor stimulation, leading to delays in acquiring language and other cognitive milestones.
The research was supported with funds from the Swan Foundation of Denver and from a National Institute of Mental Health grant.
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