Philosophers are content to hem and haw around one question for centuries without ever making an inch of tangible progress. Socrates, after all, asked questions; he didn’t answer them. But nowadays, some of the most interesting philosophical questions are scientific. Kenneth Wexler, professor of linguistics and brain and cognitive sciences, says the question he would like to see answered by science is one that is already centuries old and well worn by philosophers: how does the human mind produce and interpret language?
Sitting in his fourth-floor office overlooking Kendall Square, Wexler, who came to MIT in 1988, talks about language with the animation and enthusiasm of a researcher who is just beginning his career. He’s undaunted that the question he’s trying to answer has challenged the greatest minds in philosophy. “For the first time, I think we’re in a position to really study it,” he says.
That’s because researchers like Wexler are developing a new approach–one that combines the rich tradition of theory from linguistics with decades of data from cognitive-science research. Over the past 15 years, advances in scanning and imaging technology, along with progress in mapping the genome, have heralded hope of linking biological research ever more tightly with linguistic studies. Linguistic researchers across the country are starting to use traditional linguistic theory to drive experiments and, in turn, are feeding empirical results back into the theory. It’s a formula that works in most sciences, and one that has made Wexler a leading figure in psycholinguistics–the study of the cognitive aspects of language acquisition and use–for almost two decades.
In the late 1980s and throughout the 1990s, Wexler unraveled the details of how and when language emerges in children. He showed that some of the more complex aspects of language use develop in discrete stages. For example, certain elements of language, such as passive construction, normally show up in the speech of children between five and seven years of age–a pattern that is generally consistent across languages. Most adults understand that the sentence “John was pushed by Mary” describes exactly the same event as “Mary pushed John.” But to a young child, that relationship may not be so clear. Wexler maintains that children have trouble using and understanding the passive construction until they are about six or seven because the necessary biology hasn’t yet matured. In this view, children don’t “learn” the more complex aspects of their native language any more than they “learn” to grow adult teeth.
Wexler’s findings are now widely accepted. Nevertheless, questions about language development abound. How do toddlers pick up the subtleties and nuances of grammar without formal training and with such inconsistent and incomplete input from adults? Which linguistic faculties (if any) are present at birth, and which have to be learned? Why does language develop in stages? A classic method of determining how something works is to study what happens when it breaks. So Wexler is focusing on the speech of stroke patients and of children with genetically based developmental disorders. He hopes that by studying what happens when language breaks down, he’ll be able to address broader questions, such as which parts of the brain govern language use, and how genetics might steer language acquisition.