The Importance of Developmental Plasticity

What do I consider my most important scientific contribution? There are actually two important contributions that are intertwined – one mostly not my own, and one that is to some degree mine. The first – a contribution of great importance that came primarily from the work of Ursula Bellugi, Edward Klima, and William Stokoe – concerns the discovery that signed languages of Deaf communities around the world are natural languages, equal in expressiveness and in grammatical complexity to spoken languages. When I was in graduate school and before, most psychologists and linguists believed that human language was uniquely connected to speech – that all languages around the globe were produced with the mouth and processed with the ear.

Thanks to the groundbreaking work of Bellugi and Klima and of Stokoe, we now know that, when speech is unavailable, humans readily use their hands and eyes for communication and that signed languages can become as complex and elegantly structured as spoken languages. I am proud to have done some of my research on the structure and acquisition of American Sign Language, in collaboration with Ted Supalla, a Deaf native signer whose native language is ASL (and who is also my husband). Our work on ASL has been in the context of another passionate interest that has been the main focus of my scientific career.

My own most important contribution, I think, concerns developmental plasticity. I've long been interested in mechanisms of learning: How do we learn, what are we especially good at learning, what are the principles and constraints on the way we learn? I've been particularly interested in why infants and young children are better than adults at learning certain types of skills, especially language. This issue was first raised by Eric Lenneberg, who suggested that there may be a “critical period” for language acquisition in humans. I read Lenneberg's famous 1969 Science article in a first-year proseminar in graduate school, and then his 1967 book Biological Foundations of Language (the Science article is a précis of his book). One idea in that work is that there may be a critical period for human language learning – a window of time during which we are especially good at learning languages but not as good thereafter, even with the same amount and type of exposure.