A new study conducted by Canadian researchers suggests babies as young as four-months-old can differentiate between French and English without actually hearing the languages.
The study, published Thursday in the journal Science, found infants from four to eight months could tell the languages apart based on visual cues alone.
Researchers showed infants silent videos of people speaking either English or French.
They suggest babies can discern visual differences between the two languages by watching the shape and rhythm of a speaker's mouth and their facial movements.
"It (the study) shows us that infants are sensitive to visual properties of spoken language, one more step in putting together a symbolic, multi-modal system of communication," Dr. Athena Vouloumanos of McGill University's Department of Psychology said in a statement.
The silent videos were shown to infants aged four, six and eight months from monolingual English homes; as well as two groups of children ages six and eight months from bilingual homes.
Vouloumanos said the research takes an interesting step toward finding out how humans learn different languages. The study may have implications for adults differentiating between languages using visual cues, she said.
"Some adults say that they can tell when people are speaking French because they look like they're kissing when they make 'eu' sounds that don't exist in English," Vouloumanos said.
Vouloumanos began working on the study while she was a PhD student at the University of British Columbia before joining McGill University in 2004.
Other researchers involved in the study included UBC Research Chair and psychology professor Janet Werker and Whitney Weikum, who is a UBC Neuroscience doctoral student.
Weikum said the study is significant because researchers already knew babies differentiated languages at a very age using auditory cues, "but this is the first study to show that young babies are prepared to tell languages apart using only visual information."
While visual language differentiation occurred in infants as young as four-months-old, researchers found the ability was no longer evident as the babies aged and were limited to only one language.
Eight-month-old infants who came from English-speaking homes lost the ability to differentiate between the two languages visually.
"There is a lot of circumstantial evidence that suggests many perceptual changes occur in a child's development between the ages of six and ten months, when an infant starts to tune into the perceptual properties of speech in their native language," Vouloumanos said.
Babies growing up in a bilingual environment maintained the ability to separate the languages, which will continue to be an advantage if the child develops dual-language skills, the researchers said.
"This suggests that by eight months, only babies learning more than one language need to maintain this ability. Babies who only hear and see one language don't need this ability, and their sensitivity to visual language information from other languages declines," Weikum said.
