Children as young as 5 months old exhibit preferences for their family's unaccented native language, researchers reported this week, suggesting that speech makes a powerful first impression even very early in life.

"Babies want to interact with somebody who speaks the language they are familiar with, even though the babies themselves don't speak yet," said Katherine Kinzler, an author of the paper being published Tuesday in the journal Proceedings of the National Academy of Sciences.

Infants not only looked more often at a person who spoke their native tongue without an accent, they were more likely to accept toys from those people, the study found. Five-year-old children were more likely to desire friendship with children who spoke the same language and those without an accent.

Such early preferences may develop into criteria for making judgments about strangers, in the same way that race and gender color people's perception, the authors speculate.

In the study, American infants were shown videos of women speaking either English or French. The babies were then shown both women side by side and silent, and researchers measured how long the infant spent looking at each face.

The authors observed a preference for looking at the woman who spoke English. In babies from France, the opposite was true, with more of the infant's gaze directed at the French-speaking woman.

However, most previous studies using this "looking-time" task were unable to determine whether the infant preferred one of the choices or if it drew the infant's attention for another reason, said Mark Liberman, a professor of linguistics at the University of Pennsylvania who was not involved in the study.

"In most uses of the technique, the only conclusion that you want to draw is that the infants can tell the difference," Liberman said.

To address this concern, the researchers added a behavioral choice to the experiment. Slightly older infants who were not yet talking again viewed women speaking two different languages, followed by a video of each speaker offering the child an identical toy.

When the toys were actually presented to the children in front of the two images of the speakers, they chose the one "offered" by the native speaker more often.

"The toy choice shows that this isn't just looking preference, it's an interactive preference," Kinzler said.

In a further experiment, American 5-year-olds were shown videos of children speaking unaccented English, French or English with a French accent. The subjects were then shown pictures of the different children and asked whom they'd most like to be friends with.

Subjects preferred the English-speaking child by a wide margin compared with both the French-speaking child and the child who spoke accented English. The result suggests that children at an early age already make social decisions according to how people speak.

"The study says that not only are children able to discriminate between native and foreign languages ... they are sensitive to intra-language contrasts, like accents," said Lawrence Hirschfeld, professor of anthropology and psychology at the New School for Social Research in New York City. "That infants would be sensitive to this is very interesting."

Whether these biases grow stronger with age, and how flexible these preferences may be, remains to be studied. Previous studies found that adults make accent-based inferences about people's social class, intelligence and even height when audio recordings are played.

Although the current study looked only at children from monolingual households, the early formation of language preferences raises the possibility that exposure to more than one language early in life may weaken these biases.

"It's an open question how malleable these early preferences are, and how exposure to multiple languages might mitigate those preferences," said Kinzler.

But Hirschfeld thinks these early biases reflect a strong societal influence upon children's social attitudes that may not be fixed by exposure to multiple languages.

"Once you have a prejudiced environment, children, in this case infants, are really well prepared to fit in," he said.