According to a new study published by University of British Columbia, four-month old babies are able to tell when a speaker a speaker has switched to a different language from visual cues alone.

Whitney Weikum, a UBC Neuroscience doctoral student working with Canada Research Chair and Psychology Prof. Janet Werker, found that infants are able to identify a certain language by watching the shapes and rhythm of the speaker's mouth and face movements.

"We already know that babies can tell languages apart using auditory cues," says Weikum. "But this is the first study to show that young babies are prepared to tell languages apart using only visual information."

Weikum tested three groups of infants – ages four, six and eight months – from monolingual English homes and two groups of infants –ages six and eight months – from bilingual homes. His findings suggest that visual information alone will prompt the babies at four and six months to pay closer attention and watch the video for a longer period when the speakers switch languages.

By eight months, only babies from a bilingual French-English home and familiar with both languages were able to tell the languages apart visually.

"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."