What information do babies use to distinguish between languages?

Previous research shows that infants are born with the ability to distinguish between different languages, as long as those languages are prosodically distinct – that is, as long as they have very different rhythms and intonation patterns.  Infants cannot distinguish between prosodically similar languages – for example, English and German – until a later age, and even then, they can only distinguish between their native language and a non-native language.  It is unclear what infants are listening to in their native language that allows them to distinguish it from a non-native language.  The first part of this study tried to determine when American English-learning infants learned to distinguish their native language from German, and from Australian English.  The second part tried to determine what infants were listening to that allowed them to distinguish between the languages.

We found that 5-month-olds were not able to discriminate between American English and German, but 7-month-olds were, indicating this ability develops between those two ages.  Neither 5, nor 7-month-olds were able to distinguish between American English and Australian English, but interim results suggest that 9-month-olds might, indicated this ability develops around that age.

We then tested 7-mo-olds to determine what information they were using to discriminate between English and German – segmental, pitch (or intonation) or rhythmic cues.  To do this, we tested infants using low-pass filtered speech (removing segmental information), speech resynthesized with an artificial pitch contour and speech with a monotone pitch contour (both removing pitch information).  We found that 7-mo-olds could still discriminate between English and German after the stimuli had been low-pass filtered, but not when the pitch contours of the stimuli were replaced.  These results indicate that infants strongly attend to pitch information when discriminating languages.