It's become the norm in America for parents to capture their children's smiles, tantrums, and impish shenanigans—sometimes cute, sometimes deeply embarrassing—on blogs, YouTube videos, and Twitter feeds. But MIT professor Deb Roy makes even the most obsessive at-home documentarians seem inattentive: He recorded, on video and audio, nearly every waking moment of the first three years of his son's life—not as an exercise in parental vanity, but in the name of science. His goal was to create as complete a picture as possible of how one child learns a language. For his study, "The Human Speechome Project," he embedded 11 cameras and 14 microphones in the ceilings of his home, and set them to record for an average of 12-14 hours a day. Now Roy and his team have begun the enormous task of trying to make sense of the data—all 120,000 hours of it.
Roy's decision to use his own child as a research subject makes people uncomfortable: When the New York Times wrote a story about Roy, the comments were on the outraged side. Recording a child for amusement is one thing, but taking those recordings to the lab for analysis may be quite another. It may seem unethical—perhaps even dangerous to the child's mental health.
But it's crucial to realize that while Roy's using the latest technology, his tactic is not new: Language researchers have long used their children as subjects. All parents feel a sense of wonder as they watch their children piece together their first words, and their first phrases; scientist parents can't help but feel professional curiosity as well. Because some have given in to the pull of this curiosity and turned their observations into data, we're a little bit closer to figuring out the mystery of how humans acquire language.
One of the early notable studies of a child by his parent was published by the philosopher Dietrich Tiedemann in 1787. From Tiedemann's careful notes we learn that his son Friedrich began to communicate by pointing at 8.5 months, that he first said "duck" and "potato" at 23 months, and that he had a much easier time pronouncing p, t, and k than z, w, and sp. In those days there was plenty of philosophical discussion about the nature of children and what they knew when: Were they blank slates, or did they possess innate knowledge? Did they understand concepts before language? For the most part, these issues were debated in armchairs. Tiedemann's approach was more practical: Here is a child, let's see what he actually does. He rejected anecdotal evidence and out-of-thin-air wisdom, relying instead on carefully recorded observations. His study didn't settle the blank-slate debate at the time, but it encouraged others to try an empirical approach to scholarship. Tiedemann's conclusion—that children do, in fact, posses some pre-linguistic knowledge—has since been borne out by a couple centuries' worth of research.
In the 1800s empiricism gained in popularity and many scientists published studies of their own children, Charles Darwin among them. But it wasn't until the 1900s that parents went beyond jotting down things that struck them as interesting and started keeping thorough journals of everything their kids said. The psychologists Clara and William Stern published their Kindersprache in 1907—a detailed study of the first three years of their children's lives that catalogued the sounds, words, and parts of speech they used at various stages. Jean Piaget completed studies of his children in the 1920s. In the 1940s, the linguist Werner Leopold published four volumes of notes on every aspect of his two daughters' bilingual language development (they were raised with German and English), including a meticulous phonetic record of the girls' pre-lingual babbling stage.
The sheer size of these studies meant they could be mined by scholars for data. They offered enough information to investigate questions like: How many nouns and at what age? What kind of sounds and in which order? Such information had never been catalogued in this way or in this quantity before, and it helped advance the field of linguistics. Roman Jakobson, one of the most influential linguists of the 20th century, pulled from these studies to support his theory that languages are not collections of particular sounds, but systems of contrast. Children acquire language by sorting out the difference between, say, words articulated with the lips (labial features) and those articulated with the tip or blade of the tongue (coronal features). Put another way: They're not figuring out how to pronounce man so much as recognizing the difference between man and ban. (The former word starts nasally, the latter does not.)
Until about 1950, there was a sense in which researchers had to use their own children as subjects. How else would it be possible to get the kind of access needed to collect evidence? But advances in recording technology made it possible to gather data from a child without actually living with him. Scientists started tape-recording interactions between children and their parents for a few hours at a time, either in the home or in the lab. And the birth of cognitive science introduced a new method for looking at child language: the controlled experiment. You didn't have to look at everything the child did, you could just come up with a specific hypothesis and then test it. In 1958, for example, Jean Berko Gleason developed her famous "Wug Test." By asking a brief series of fill-in-the-blank questions, such as "This is a wug. These are two …?" she showed that even very young children internalize the word-building rules of language and can produce correct examples of those rules ("wugs") that they had never heard before.
Yet researchers continued to use their own children as subjects, because the practice was always and will always be more than a matter of convenience. It's not as if scientists have children in order to test out a theory. Rather, they have children and then find that the experience of watching them acquire language raises all sorts of questions. Then they follow where the children lead them.
In 1962, Ruth Weir published Language in the Crib, a study of the monologues her toddler son produced alone, while drifting off to sleep. A senior colleague of hers had a hard time believing that children really did this—they are learning language from others at that stage; why would they talk to themselves?—so he asked around, and all the mothers he talked to said, "Of course! Children do this all the time!" Any mother could notice this behavior; it took a linguist mother to identify it as an area for research. The monologues of Weir's son showed that very young children rehearsed and experimented with linguistic structures on their own. And the study of "crib talk" became a new way to find out how toddlers come to understand the world.