Out of the Mouths of Babes: The effect of source on 20-month-olds' Use of Mutual Exclusivity

Out of the Mouths of Babes: The effect of source on 20-month-olds’ Use of Mutual Exclusivity Chandra L. Brojde (chandrab@colorado.edu) Department of Psychology, CB345 Boulder, CO 80309 USA Eliana Colunga (colunga@psych.colorado.edu) Department of Psychology, CB345 Boulder, CO 80309 USA Abstract One account of word learning suggests that children learn that words are unique as labels among perceptual signals because of the way they tend to systematically co-occur with catego- ries of objects. Twenty-month-old’s use of mutual exclusivity with different types of labels emanating from different sources was investigated in order to evaluate this account. Specifically, words and animal sounds were investigated. Re- sults showed that children applied mutual exclusivity to both words and animal sounds produced by mouths, but not to words or animal sounds produced by noisemakers. This sug- gests the importance of including the regularities of social context and pragmatics to the associationist account of word learning. Introduction By the time children are two years old, most have gained a large vocabulary of words, mostly made up of nouns that refer to objects in their world (Goldin-Meadow, Seligman, & Gelman, 1976). But how they do this is still somewhat of a mystery. In order for children to learn a novel word for a novel object they must first recognize the signal as a linguis- tic signal (word) rather than an arbitrary non-linguistic sig- nal (sounds and hand gestures). For instance, when a par- ent points to a dog while at the same time naming it as a dog, and maybe imitating a barking sound, how does the child know that the word is what the parent means to use to label the dog? How does the child know that the non- linguistic signals (pointing gesture and animal sound) are not referring to the dog? In this paper, we address this ques- tion by asking in which situations children treat different types of signals produced by different sources as labels for categories; in particular animal categories. Development of Word Form Associations The special status of auditory signals may begin early in development. Robinson and Sloutsky (2004) found that auditory signals overshadow visual information in 8-month- olds. A distinction between linguistic and non-linguistic sounds and their effect on attention to objects emerges at around that time too. Although both linguistic and non- linguistic sounds, seem to encourage 9-month-old infants to attend to objects, only linguistic, but not non-linguistic sounds, facilitate categorization (Balaban & Waxman, 1997) and individuation of objects at this age (Xu, 2002). The preference for linguistic sounds as labels for object categories appears later in development. Early on in lan- guage acquisition, children will accept both linguistic and non-linguistic signals as labels for novel objects that they encounter (Namy, 2001; Namy & Waxman, 1998, 2002; Woodward & Hoyne, 1999). But as children get older they begin to accept only words as possible labels for categories. In one study, Woodward and Hoyne (1999) tested whether 13-month-olds would accept linguistic sounds (words) produced by the experimenter and non-linguistic sounds (squeaks and beeps) produced by a noisemaker as labels for objects in a forced-choice task. Both a training session and a test procedure were included during which children were presented with novel objects and novel words and sounds in a joint-attention setting. Throughout the train- ing procedure, children were shown a novel target object that was paired with either a novel word or a novel sound. A second distracter object was also presented but not la- beled. The test trials consisted of asking the children to “Get the ”, the label being the original novel word or sound presented during the training session, and giving them the target object and the distracter object to choose from. In a separate control condition children were simply asked to “get one. ” Results showed that the 13-month-olds chose the target object more often than chance for both the sound and word conditions but not the control condition. Thus, at 13-months of age children accepted both words produced by an experimenter and sounds coming from a noisemaker as labels for objects. Similar studies by Namy and Waxman (1998, 2002) have also shown that at 18-months of age children will accept gestures in addition to words as labels for objects. Further- more, it has been suggested that at this very young age chil- dren’s word learning encompasses many different types of signals including not only words, sounds and gestures, but possibly even pictograms (Namy, 2001). Later on in development, the type of signals that are ac- cepted as labels for object categories becomes more con- strained. In a separate condition conducted by Woodward and Hoyne (1999), 20-month-old children accepted words but not non-linguistic sounds as labels. Likewise, in a simi-