Cross-situational language learning: The effects of grammatical categories as constraints on referential labeling

Cross-situational language learning: The effects of grammatical categories as constraints on referential labeling Padraic Monaghan (p.monaghan@lancaster.ac.uk) Karen Mattock (k.mattock@lancaster.ac.uk) Department of Psychology, Lancaster University Lancaster LA1 4YF, UK Abstract Infants learn to map words onto situations, even though there is a bewildering array of potential referents for each word in their environment. Previous studies of cross-situational learning have shown that learning correspondences between words and referents is possible, when all words refer to objects. However, in child-directed speech, the infants’ primary input is more complex as it comprises multi-word utterances from different grammatical categories, some of which do not form word-object pairings. In study 1, we confirmed in corpus analyses of child-directed speech that utterances typically contain words from several different grammatical categories. In study 2 we confirmed that participants could still learn from cross-situational statistics when (1) the language also incorporated words that did not refer to objects, and (2) when the language additionally contained function words that marked the referring and non- referring words. Cross-situational learning is robust to grammatical categories in acquiring word-object pairings. Learning to map words onto objects How do infants acquiring their first language learn to map words onto referents in their environment? In 1960, Quine illustrated the complexity of this task by describing the situation of a field linguist trying to determine the meaning of the word “gavagai” spoken by a native speaker as he points to a rabbit running past. The referent for the word could be the rabbit, but it could also be the action of running, a patch of fur, the general beauty of the scene, or infinite other interpretations. Additional constraints must be available to the learner in order to correctly ascertain the intended referent. The developmental literature reports several candidate constraints that reduce the space of possibilities, such as the whole-object constraint (Markman, 1990), whereby infants seem to assume that the referent for a word is a whole object and not a part of it. However, such perceptual constraints are still not sufficient to confine the interpretation to a single referent as there are often situations where the child’s environment contains several separate but whole objects. In the same paper, Markman (1990) reports other possible constraints that arise from the child’s computation of statistical co-occurrences between words and objects in the environment that can assist in solving the “gavagai” problem. Smith and Yu (2008) illustrated one such statistical constraint in action by indicating that 12-month old infants could learn the relationship between particular names and objects across multiple learning situations, known as “cross- situational learning” (Siskind, 1996). In their study, six nonsense words and six unfamiliar shapes were paired. For each learning trial, participants heard two words and viewed the two objects to which they referred, and had to learn which of the words referred to which of the objects. The probability of hearing a word and seeing the target object was therefore 1, but the probability of hearing a word and seeing another of the objects was . 2. After training, infants were presented with two objects and heard the word paired with one of those objects, and were found to preferentially look toward the target object. The infants were shown to rapidly determine across multiple learning trials the co- occurrence between names and objects. Yu and Smith (2007) conducted a similar study for adults, but examined the effect of the number of words and objects presented at any one time. When the number of words and objects presented at any one time was either two, three, or four, the participants learned better than by chance the relationship between the target name and the target object. As with the infant study, adults could learn the link between particular words and objects from co-occurrences across several learning situations even when there were several – up to four – possible referents for each word. However, in both these previous studies the association between a particular word and object in each learning situation was perfectly represented, in that for every word spoken there was an object to which it referred. This has the consequence that means that in the learning situation multiple factors may have been contributing to learning. First, the cross-situational association between each word and each object across multiple instances was a contributor, as highlighted by Smith and Yu (2008). Second, learning of one of the word-object pairs could assist in learning the relationships between the other word and object (as in Akhtar, 2002). Hence, another influence on learning in these studies could be the mutual exclusivity constraint of names for objects (Houston-Price, Plunkett, & Harris, 2005; Markman, Wasow, & Hansen, 2003), whereby learning of a name for one object precludes the child from using the same name for another object. So, learning the cross-situational statistics could be boosted in that knowing the connection for one of the word-object pairs provides information about the referent for the other word(s) that the participant hears. The cross-situational learning studies are useful abstractions from the real-life learning situations present when infants acquire knowledge of referents for words, yet they do not represent the natural situation in two potentially important respects. First, all the words in these situations have referents, whereas this is not the case in child-directed