Understanding “Double Dipping” in Bilingual Babies’ Language Learning

Imagine a baby growing up in a bilingual home, hearing both English and Spanish every day. One might think that the more the baby hears English, the less attention they would pay to Spanish—especially if English dominates their daily interactions. But in our study, we found something surprising: babies with more English exposure were still paying close attention to Spanish sounds. That is what we call double dipping—using input from one language to help process another.

Here is how it works.

When babies hear the same sound in two languages—like the letter D, which is pronounced a bit differently in English and Spanish—their brains have to figure out which version belongs to which language. English speakers tend to pronounce the D quickly and without voicing beforehand, while Spanish speakers often add a short buzz (called pre-voicing) before saying the D.

Now, if a baby hears English most of the time, you would expect their brain to tune in mostly to English sounds. But when we measured their brain responses, we saw something unexpected. Babies with more English input were still responding to Spanish D sounds as if they were important, even though they did not hear Spanish as often.

Why?

We think the answer lies in how their caregivers speak. In bilingual homes, even when caregivers speak English, their pronunciation might still carry traces of Spanish—what we might call an accent. This accented English can actually help babies recognize and learn features of both languages at once. So instead of choosing just one set of sounds to focus on, these bilingual babies are using the English they hear and the Spanish features hidden within it to build a broader understanding of speech sounds. They are, in essence, “double dipping”—getting twice the learning from the same input.

On the other hand, babies who hear mostly Spanish did not show the same attention to English contrasts. This is likely because Spanish-speaking caregivers produce Spanish sounds very clearly and consistently, without blending in English patterns. That means English is not sneaking into their input the same way Spanish is sneaking into the English of bilingual caregivers.

In short, what babies hear—and how they hear it—matters a lot. The accents, the mix of languages, and the way caregivers pronounce sounds all shape the baby’s developing brain. And in bilingual households, babies may be picking up more than we think, learning from both languages even when one seems to dominate.

That is the power of double dipping.

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