The birth of the statistical learning literature is often traced back to Reber始s (1967) seminal study on implicit learning using an artificial grammar learning paradigm. However, to fully understand the relationship between such early implicit learning studies and the current notion of statistical learning, it is important also to consider its conception. The theory of perceptual learning by J. J. Gibson and Gibson (1955) paved the way for accounts of learning with a basis in sensory experience. In the Gibsons始 theory of perceptual learning, which has close parallels to current ideas about entrenchment (Schmid, 2007), repeated experience with a percept enhances one始s ability to discriminate between it and other percepts. This chapter argues that a communicative system characterized by entrenchment, as posited in this volume, likely relies to a considerable extent on the ability to track, learn, and use underlying associative relationships between linguistic elements and structures in comprehension and production. When considering the origin of statistical learning as a theoretical construct, it is also important to consider the early work of Miller and Selfridge (1950), who thought that a reliance on transitional probabilities may be similar to the way in which grammar is learned. Other research informed by both Miller始s work and the theory of perceptual learning espoused by J. J. Gibson and Gibson (1955) demonstrated that frequent co-occurrence due to underlying structure improved participants始 recall of letter sequences (Miller, 1958) and that learning the positional relationships between linguistic units (i.e., morphemes) occurs as an experiential process of familiarization with the temporal positions in which such units are frequently encountered (Braine, 1963). This laid the foundation for future research investigating the close relationship between frequent co-occurrence and the strength and automaticity of recall at various levels of linguistic analysis. From the beginning, research on implicit learning related to language was focused on the way(s) in which units of linguistic information are formed. Some of the early explanations for the ways in which this learning happened relied on experiencebased accounts, as just described. However, experience-independent theories of language acquisition quickly became the dominant perspective primarily because of the widespread acceptance of the "poverty of the stimulus" argument (Chomsky, 1965; Crain, 1991). Saffran, Aslin, and Newport始s (1996) research gave the psychology of