That's what UBC psychologists Prof. Janet Werker and graduate student Christine Stager are trying to find out.
"We know a lot about language acquisition around age two, but less about the period between one and two years," says Werker, who has spent more than 20 years studying language acquisition in infants. "We're interested in understanding how babies move from being sensitive to the sounds of language to mapping those sounds onto words."
Until Werker and Stager published the results of their most recent three-year study in the scientific journal Nature, researchers didn't know what information babies stored as they learned new words.
"We now realize they're storing less than we thought," says Stager.
During their first year, babies listen carefully to the sounds of the language spoken around them. By 10 to 12 months they can distinguish between consonants and vowels spoken in their native language from the same syllables spoken in another language.
At around 14 months a change occurs.
Werker and Stager discovered that at that point babies begin to ignore some of their previous information so they can focus on learning words.
"They're efficient little problem-solvers," says Werker. "They focus on what's needed and drop what's not. It's an automatically assured process in learning language."
To make the discovery, the researchers observed 64 babies' reactions to word-object pairings.
Brightly-coloured moving objects were shown on a monitor in front of the baby. As objects appeared, they were paired with the syllables "bih" and "dih," announced through a speaker.
When first exposed to the pairings, babies showed their attention by concentrating on the screen. After the same pairings had been seen repeatedly, their attention wandered.
Werker and Stager watched to see if babies noticed a difference when objects or syllables were switched.
In a previous study Werker had found babies at this stage were capable of distinguishing between the sounds "bih" and "dih," yet in this study they acted as if they were the same syllable.
"All their attention is focused on matching the sound with the object," says Stager. "They're already working at full capacity. To get the job done, some detail gets ignored."
At ages three to four, when word learning is no longer difficult, infants return to distinguishing between subtle phonetic differences.
Understanding these stages in language development may be useful in working with children with delayed language or learning disabilities, says Werker.