Infants Rapidly Learn Words from Noisy Data via Cross-Situational Statistics

Infants Rapidly Learn Words from Noisy Data via Cross-Situational Statistics Linda Smith (smith4@indiana.edu) Department of Psychological and Brain Sciences, and Cognitive Science Program, Indiana University Bloomington, IN 47405 USA Chen Yu (chenyu@indiana.edu) Department of Psychological and Brain Sciences, and Cognitive Science Program, Indiana University Bloomington, IN 47405 USA uncluttered as the experimental settings in which fast- mapping has been demonstrated. In everyday contexts, there are typically many words, many potential referents, limited cues as to which words go with which referents, and rapid attentional shifts among the many entities in the scene. It is possible that young learners just ignore the information in such highly ambiguous learning contexts and wait for contexts in which the referents of heard words are more certain (Brent & Siskind, 2001). However, a more optimal learner might be expected to make use of all the available data. Second, the evidence indicates that 9-, 10-, and certainly 12-month old infants are accumulating considerable receptive lexical knowledge (Fenson et al, 1994; Swingley & Aslin, 2000). Yet many studies find that children even as old as 18 months have difficulty in making he right inferences about the intended referents of novel words (e.g., Katz, Baker & Macnamara, 1974; Moore, Angepoulos B Hirsh-Pasek, Golinkoff & Hollich, 1999; Pruden, Hirsh-Pasek, Golinkoff & Hennon, 2006). There are studies showing that infants as young as 13 or 14 months (Woodward, Markman & Fitzsimmons, 1994; Woodward & Hoyne, 1999; Schafer & Plunkett, 1998; but perhaps not younger, Werker, Lloyd, Cohen, Cassola & Stager, 1998) can link a name to an object given repeated unambiguous pairings in a single session. Overall, however, these effects are fragile with small experimental variations often leading to no learning (see especially, Woodward & Hoyne, 1999; Werker, et al, 1998; also Oviatt 1980, 1982; and Bloom 2000 for a discussion). This raises the possibility that there might be some other way that young children learn word- referent mappings. The experiment reported here shows for the first time that infants rapidly learn multiple word-referent pairs by accruing statistical evidence across multiple and individually ambiguous word-scene pairings. The indeterminacy problem is solved not in a single trial but across trials, not for a single word and its referent but for a system of many words and referents. This learning is shown to be sufficiently rapid and robust that it could play a significant role in early lexical learning. Figure 1 illustrates how cross-trial statistics might work. The learner hears the unknown words “bat” and “ball” in the context of seeing a BAT and BALL. Without other information, the learner cannot know whether the word form “ball” refers to one or the other visual object. However, if subsequently, while viewing a scene with the potential Abstract First word learning should be difficult because any pairing of a word and scene presents the learner with an infinite number of possible referents. Accordingly, theorists of children’s rapid word learning have sought constraints on word-referent mappings. These constraints are thought to work by enabling learners to resolve the ambiguity inherent in any labeled scene to determine the speaker’s intended referent at that moment. The present study shows that 12- and 14-month old infants can resolve the uncertainty problem in another way, not by unambiguously deciding the referent in a single word-scene pairing, but by rapidly evaluating the statistical evidence across many individually ambiguous words and scenes. Keywords: language acquisition, word learning. Introduction The pairing of a word and a scene is not enough to determine the meaning of the word. To illustrate this point, Quine (1960) famously imagined a stranger who hears a native say “gavagai” and points to a scene. To what does “gavagai” refer -- a rabbit, the grass, a tree, the rabbit’s ears, or perhaps the beauty of the whole? Even if one assumes a perceptual system that segments the scene into separate objects and an attentional system biased towards objects, the intended referent is indeterminate from this one experience. Infants are like strangers who do not know the native language, yet they solve this indeterminacy problem. This paradox -- the uncertainty of the referent in word-scene associations and the fact that infants learn object names nonetheless --is a core theoretical problem in the study of early word learning. For the past 30 years most research on children’s word learning has concentrated on how the learner resolves the ambiguity at the moment the novel word is first encountered. Experimental studies leave no doubt that by the time they are 2 years old children do this at least for object names. That literature points to attentional (Smith, 2000), social (Baldwin 1993, Tomasello, 2000), linguistic (Gleitman, 1990) and representational (Markman, 1990) constraints as crucial to children’s ability to resolve referential ambiguity and fastmap a word to its intended referent. There are two reasons to suspect that this one-encounter solution to referential uncertainty is not the only (or even the most important) mechanism of early word learning. First, not all opportunities for word learning are as