Oct. 23 (HealthDay News) -- Children as young as 5 months old are able to tell the difference between human speech and monkey calls, a new study has found.

Researchers showed 5-month-old infants from English- and French-speaking homes pictures of human faces and rhesus monkey faces paired with either human speech or monkey calls. The infants looked longer at pictures of human faces when human speech was presented and longer at monkey faces when monkey calls were played.

However, the babies weren't able to match human non-speech sounds, such as laughter, to photos of human faces. This suggests that infants are especially attuned at an early age to some of the functional properties of speech, said the researchers from New York University and McGill University in Montreal.

In another experiment, human speech, monkey calls and duck sounds were played for the infants while they were shown human and duck faces. The infants didn't look longer at the duck face when they heard a duck sound, which suggests they're unable to match ducks' faces with their sounds.

The researchers concluded that "infants' expectations about the sources of vocalizations seem not to be based on a simple association between faces and voices and extend beyond their specific experiences," according to a news release from NYU. "This ability may help infants identify their conspecifics even when they are out of view and allow them to identify the human-produced speech sounds that are relevant for language acquisition."

The study was published recently in the Proceedings of the National Academy of Sciences.

SOURCE: New York University, news release, Oct. 19, 2009