A central scientific problem in phonology is how children rapidly and accurately acquire the intricate structures and patterns seen in the phonology of their native language. The solution to this problem lies in part in the discovery of the right formal theory of phonology, but another crucial element is the development of theories of learning, often in the form of machineimplemented models that attempt to mimic human childrens' ability. This chapter is a survey of work in this area. 2. Defining the problem Before we can develop a theory of how children learn phonological systems, we must first characterize the knowledge that is to be acquired. Traditionally, phonological analyses have focused on describing the set of attested words, developing rules or constraints that distinguish sequences that occur from those that do not. Although such analyses have proven extremely valuable in developing a set of theoretical tools for capturing phonologically relevant distinctions, it is risky to assume that human learners internalize every pattern that can be described by the theory. Indeed, it is entirely possible that there are systematic patterns that hold true of the lexicon either by sheer accident or because of a series of independent historical changes (Ohala 1981 Listener; Bybee 2001 Phonology; Blevins 2004 Evolutionary; Blevins and Garrett 2004 Metathesis; Yu 2004 Explaining). A theory of human learning should be held accountable for only that knowledge that native speakers can also be shown to have learned. Accordingly, we think it is best to begin by sticking to observables, that is, behaviors and intuitive judgments that reflect phonological knowledge that speakers demonstrably possess. We believe that one of the most powerful demonstrations of phonological knowledge is generalization of the pattern to unknown words. Using this criterion, we find support in the literature for at least three distinct types of phonological knowledge. 1 Speakers possess phonotactic knowledge, meaning that they know, at least tacitly, what constitutes a legal word in their language. Halle (1978 Knowledge) gave an oft-cited example in 1 A side note: for reasons of space we will have nothing to say about a topic of great importance and relevance; i.e. phonetic learning. By this we include the induction learning of phonological categories (features, segments) from waveforms (studied by, e.g. Mielke 2005 Modeling; Lin 2005b Learning features; Maye, Werker and Gerken 2002 Infant sensitivity), language-specific patterns of phonetic realization (e.g. Keating 1985 Universal; Kingston and Diehl 1994 Phonetic), and the vast amount of free variation seen at the phonetic level (as in, for example, coarticulation; Fowler (1981 Coarticulation), Manuel and Krakow (1984 Universal), Smith (1992) Temporal). All phenomena covered here are characterizable at the level of contrasting surface entities. Albright/Hayes Learning and learnability in phonology p. 2 2 See for instance the classic study of Smith (1973 Acquisition), and for a careful overview of...
