Long before they say any words, human infants begin to babble endearingly. But graduating from simple babbles like ba-ba-ba to more complex coos like ba-goo-gi is a longer and more difficult process than researchers previously suspected, according to a study published in the journal Nature in June. And, the researchers found, the process is similar in humans learning language and in songbirds learning new melodies.

In the study, researchers Ofer Tchernichovski, PhD, and Dina Lipkind, PhD, of the City University of New York's Hunter College, and their colleagues found that for both birds and babies, the stumbling block is not learning individual sounds (or notes), but instead learning to transition between sounds. For both species, transitions must be learned individually. In other words, learning to say "goo-gah" does not make it any easier for a baby to say "gah-goo." Learning to speak, then, is a slow and painstaking process.

In the first part of the study, the researchers trained finches to learn a new song. Usually, a finch knows only one song — for example, a pattern of notes that could be abbreviated "ABC-ABC." Lipkind trained the birds to learn a new song composed of the same notes in a different order, like "ACB-ACB." But in doing so, she found that the birds had to learn each new transition one-by-one, first learning "AC," for example, then "CB" and finally "BA." The retraining process took several weeks.

Next, the researchers wondered whether they might see the same pattern in human babies. To try to find out, co-authors Gary Marcus, PhD, and Doug Bemis, PhD, of New York University, analyzed recordings from an existing database of infants who had been recorded every two weeks between the ages of 9 and 28 months. They listened for how the children transitioned from simple repetitive babbling, like ba-ba-ba or da-da-da, to more complex utterances, like ba-goo-gi. They found that, like the birds, the babies didn't make the transition all at once. Instead, they had to learn every transition between syllables separately. On average, it took the babies about five months to learn to link every syllable to every other syllable.

"It's a long bottleneck in learning," Tchernichovski says. "Just like it's a long bottleneck for the birds."

— Lea Winerman