Right after the turn of the century, Pat Kuhl, who studies speech and hearing at the University of Washington, ran a pair of experiments with English-speaking nine-month-old babies. Parents brought their infants to her lab 12 times for 25-minute sessions, with the group divided into two. One group spent the sessions with a native Mandarin Chinese speaker who sang, played, and spoke with the infants; the other did the same activities in English. After 12 sessions, the researchers measured how well the babies could distinguish Mandarin Chinese sounds. The babies had basically become native listeners: they could recognize as many sounds as infants raised in Taiwan.
Kuhl and her researchers then ran a second set of experiments, this time with the same researcher doing the same songs and activities and chatter, but on a TV. A different group listened to an audio recording. The babies in these experiments learned nothing.
Kuhl’s findings may seem relevant to the debate over the merits of screen time, or the benefits of raising bilingual babies. To scientists, the experiments suggested something far more radical: infants are highly social learners—that is, they learn by being connected to people and feeling safe. One of the breakthrough findings of the research was “recognizing that social interaction was at the core of how human brains develop,” says Kathy Hirsh-Pasek, a professor of psychology at Temple University. “It was the special sauce.”