Bootstrapping language: Are infant statisticians up to the job?

Over the years, spoken language acquisition has attracted the attention of intellects from many disciplines. After much debate, two facts are apparent. On the one hand, it is clear that the ability to learn a language must be at least partially built in to our human psyche. Even chimps, our closest evolutionary cousins, fail to learn spoken language the way human children do. This is true even if they are cared for and spoken to as if they were human children (Terrace, Petitto, Sanders, and Bever 1979; see, however, Savage-Rumbaugh and Fields 2000). On the other hand, it is also clear that human language acquisition crucially depends on experience. Infants exposed to French learn French, infants exposed to Swahili learn Swahili (see also Curtiss 1977). But what must be inherited and what must be learned? And how do infants learn what they need to learn? All current models of language acquisition represent di¤erent answers to these very basic questions. Currently, many of the most popular models of early language acquisition are what could generally be described as distributional models. Most of these models place a heavy burden on the learning capabilities of prelingual infants. Some researchers working within the distributional framework strive to show how much children could accomplish in the absence of innate linguistic knowledge (e.g. Elman 1999), whereas others still emphasize the importance of linguistically-motivated constraints or expectations in statistical learning (e.g. Gervain, Nespor, Mazuka, Horie, and Mehler 2008; Mehler, Pena, Nespor, and Bonatti 2006; Yang 2004). The main focus of this chapter will be to examine distributional learning with the goal of better understanding what exactly we do and do not know about the ability of infants to extract linguistic generalizations from the speech signal. Although the discussion presented in this chapter is meant to apply to many levels of spoken language acquisition (e.g. phonology, morphology, syntax), the examples used to illustrate my points will be drawn primarily from the infant word segmentation literature. This