Mothers are more likely to respond to their infant's vocal cues than fathers, and infants respond preferentially to mother's voice, according to a new study.
Researchers also found that mothers may be more likely to vocalize back and forth with female babies compared to male babies.
"We know that talking and playing with an infant improves cognitive and language skills," said senior author Dr. Betty R. Vohr of the pediatrics department at Women & Infants Hospital in Providence, Rhode Island.
"Early conversations start in infancy and infants appear primed to communicate shortly after birth," Vohr told Reuters Health by email. "Both mothers and fathers can play an important role in their infant's developmental progress."
The study included 33 infants born to two-parent households. The babies wore speech-activated recording devices in customised vests for 10 to 16 hours in the hospital at birth, again at about one month old, and again at seven months old.
Researchers analysed the recordings for adult word count, infant vocalizations and conversational exchanges. "The findings of female and male adult speech reflecting the actual mothers' and fathers' speech was based on logs the families kept for each recording," Vohr and colleagues reported in Pediatrics.
Even though very young babies do not yet speak, they do vocalize and can have reciprocal "conversations," Anne Fausto-Sterling said.
Fausto-Sterling, the Nancy Duke Lewis Professor of Biology and Gender Studies in the Department of Molecular and Cell Biology and Biochemistry at Brown University, was not part of the new study.
The researchers found that infants were exposed to more speech from females than males at each time point. Female adults also responded more frequently to infant vocalizations than male adults.
"It's not very surprising because mothers are more involved in childcare," Fausto-Sterling told Reuters Health by phone. "Infants hear women talk more than they hear men talk and learn to identify female voices first."
To newborns, adult females spoke an average of 1,263 words per hour on the recordings, compared to 462 words per hour for male adults.
Mothers responded more to baby girl vocalizations at birth and at one month old, the researchers found.
"This was an unexpected finding and deserves replication," Vohr said. "We know that it is important for both parents to talk, play and be engaged with their infant."
"At the moment all we can say is that adult talk appears important for encouragement of infant vocalizations and conversation turns in early infancy," she said.
A previous study by Vohr and colleagues of preterm infants using the same recording software showed that the more parents talked and had conversation turns with their infant in the neonatal intensive care unit, the higher the child's cognitive and language skills at 18 months of age, she noted.
"At least within the standard psychological literature there has been a longstanding view that girls develop language skills more quickly than boys," Fausto-Sterling said.
Some researchers believe the difference in language development is innate, but this study suggests that adults may treat infant girls differently than infant boys at a very young age, which may help explain the difference, she said.
"Not very many people have looked at children this young, preverbal kids, whether the input they're receiving has a gender imbalance," she said.
To confirm that reciprocal vocalizations with adults in infancy are linked to langue aptitude later on, a new study would need to follow children from birth through when they are old enough to talk, she said.
In the meantime, "it's certainly not gong to hurt anything to tell dads to talk more to their kids," Fausto-Sterling said.
"Both parents and in fact all caregivers need to be told about the importance of talking, singing and playing with their infant or child," Vohr said.