A new study finds infants can make sense of language much earlier than was previously thought.

The study tested whether words help babies categorize things. Northwestern University researchers showed three and four-month olds pictures of fish and dinosaurs. To half the babies, they played a verbal phrase, with a made-up word for each kind of animal.

TAPE: Look at the modi! Do you see the modi?

To the other, they just played tones.

TAPE: Tones

Then Doctor Susan Hespos and her colleagues measured the babies’ eye movements to see if they were grouping like animals together.

HESPOS: Language causes them to form this category, but the tones do not.

That puts precursors to language comprehension earlier in development than scientists had thought – before, even, most babies can roll over. She says that may help explain why parents feel compelled to talk even to newborns.

HESPOS: Developmental psychology tends to prove what every grandmother already knows.

The findings are published in the journal, Child Development.