We all use baby talk when we babble with bundles of joy, but does how we talk to infants vary across cultures?
The answer seems to be yes and no.
"Some cultures talk more or less to babies, some not at all," said Mark VanDam, assistant professor of speech and hearing sciences in the Elson S. Floyd College of Medicine at Washington State University.
"Overall, however, the impulse and act of infant-directed speech seems to be pretty human, not necessarily culturally defined," he said.
Here is a sampling of how moms and dads from around the world use infant-directed speech or "baby talk," and why.
How baby talk might be consistent
Mothers around the world consistently alter their voices when talking to their babies, no matter what language they speak, according to a study published in October in the journal Current Biology.
Researchers recorded and analyzed the voices of 24 moms with a powerful machine-learning algorithm.
Half of the women were English speakers, and the others spoke Spanish, Russian, Polish, Hungarian, German, French, Hebrew, Mandarin and Cantonese.
Despite their native languages, the study showed, all of the women consistently shifted their timbre -- or the tone and sound of their voice -- when interacting with their infants.
The researchers were surprised that this shift in sound was a consistent pattern across such a diverse range of languages, said Elise Piazza, associate research scholar at Princeton University and lead author of the study.
"After we controlled for pitch, we still found timbre differences between infant-directed speech and adult-directed speech," Piazza said.
Though some similarities have been seen in how mothers speak to babies, studies have also spotted some cultural differences among both moms and dads.
How baby talk might differ
A study published in February in the journal Child Development found that dads in North America tended to slow their speech when talking to infants, whereas dads in the Pacific island nation of Vanuatu did not. Rather, they tended to shift their pitch more.
Researchers examined 30 interactions between the fathers and their infants, around 7.8 months old. More research is needed in a larger sample of fathers to determine that such differences do, indeed, exist in how these dads baby talk.
"These are small samples," said Greg Bryant, a cognitive scientist at the University of California, Los Angeles. He conducted the study with Tanya Broesch, assistant professor in the department of psychology at Simon Fraser University.
"The bigger picture is that there are many ways that mothers and fathers can achieve the same communicative effect," he said. "What's universal is that parents often do change their voice when speaking to young children, but how they change exactly could vary across cultures."
As for mothers, a study published last year in the journal PLOS One found a tendency for Lebanese mothers to use more infant-directed speech than American moms.
The study involved 19 American and 19 Lebanese mothers. The researchers recorded audio of the American moms interacting with their infants in a lab and the Lebanese moms interacting with their infants at home.
The key difference between the groups was that Lebanese moms had a higher rate in utterances per minute of baby talk than the American moms, the researchers found.
Although other research groups have identified differences in baby talk across cultural contexts, this study was the first to report quantitatively on such language differences, the researchers wrote.
Still, the study had some limitations. For instance, American moms were tested in a lab, but Lebanese mothers were tested at home, which could explain the differences.
On the other hand, it turns out that how babies respond to their parents could vary by culture.
How babies babble around the globe
"Babies will often babble with their native sound-sequences," VanDam said.
"For example, we don't have words in English that begin with 'tl,' such as 'tlick,' and English-speaking babies don't tend to babble that way," he said, but some Spanish words begin with "tl."
"We also see sign language babies babbling in sign language, which is fairly strong evidence that it's more of a human trait than some language or culture specific trait," VanDam said.
In other words, as kids develop, their babbling starts to reflect the speech patterns of their native language, Bryant said.
A study published in the Proceedings of the National Academy of Sciences in November suggested that infants start understanding words around 6 months old.
"So mothers and fathers exaggerate vowel categories, for example, so they'll make vowel sounds a little more noticeable, and then that helps the infants acquire the vowel sounds of their language," he said.
"Some people also think that exaggerated features in infant-directed speech help kids learn how to parse the syntax of spoken sentences, but that is a little more controversial," he said.
The changes we tend to make in our voices -- such as exaggerated, repetitive and high-pitched baby talk -- could actually be useful for babies' learning, Piazza said.
"Previous experiments have shown that infants segment words and learn the meaning of novel words better from infant-directed than adult-directed speech," Piazza said.
"It also seems to help parents capture babies' attention and engage them emotionally," she said. "Adults are generally motivated to engage infants, and they intuitively know that babies respond well to the exaggerated patterns in baby talk. Infant-directed speech is just one example of tailoring your communication style to a particular audience, which we do all the time."
Why we use baby talk
Some scientists argue that baby talk not only helps infants acquire language, it helps parents form a positive emotional bond with their babies, said Linda Polka, a professor in the School of Communication Sciences and Disorders at McGill University in Canada.
Other studies suggest that infants prefer high-pitched infant-directed speech and even infant-directed singing, Polka said.
The reason for this preference remains complex, but research suggests that when adults shift the sound of their voices for "baby talk," that causes them to sound smaller -- as if their voice is coming from a smaller vocal tract, Polka said.
"Our research shows that babies prefer to listen to speech coming from a smaller infant talker, but we don't know exactly why babies show this preference. Do they simply have a general 'smaller talkers are better' bias, or are they particularly sensitive to how big an infant is?" Polka said.
In the future, "we could figure this out by assessing how they respond to speech sounds that come from a vocal tract that is too small to be an infant. Would they still like it, or would that be less interesting to them?" she said.
Additionally, Polka said that whether you are talking to a baby or an adult, research suggests that there is a tendency to shift your speech to sound more like the person who you are interacting with.
"You are more likely to do that when you have a positive regard for the person you're interacting with," Polka said.
"Adjusting our speech to sound smaller when we use baby talk may be a way to convey affect to the baby, by trying to sound like them," she said. "At the same time, it can also help them in terms of their own learning, because we're giving them a chance to listen to a voice that sounds more like them. We may be kind of priming them for their own voice, which is quite distinct from an adult voice."