A Memory Account of Children ’ s Failure to Generalize Novel Names to Novel Instances and Novel Scenes

When they learn novel names, young children are thought to perfectly segregate an object from its environment and to associate it with its name no matter the scene in which the object is included and, in a post-test, to designate the correct object in novel scenes or contexts and to generalize the association to new instances that might differ from the original object according to various dimensions. We show, in two experiments, that children aged three do not always generalize new names across contexts and across instances even when instances are categorized in the same set as the learning stimuli. These results suggest that novel name generalization is, to some extent, independent of conceptual generalization. These results are interpreted in terms of general mechanisms of memory: it is argued that a failure to generalize novel words to novel stimuli or to new contexts might result from a lack of retrieval cues. Young children are supposed to be proficient learners of novel names. Each day, young children learn new lexemes (Fenson, L., Dale, P., Reznick, S., Bates, E., Thal, D., Pethick, S., 1994). One important dimension of the task is to associate each novel word with the appropriate referent in the world and to be able to use this association for future namings. Creating the association is an instance of a general and fundamental learning mechanism (Siegler, 1997). Children can learn a novel category name from hearing its name only once (Smith, 1999). This ability is well captured by the notion of fast mapping. Children can grasp aspects of the meaning of a new word on the basis of a small number of incidental exposures, without any explicit training or feedback (Carey & Bartlett, 1978; Bloom, 2000 for an overview). Carey and Bartlett (1978) showed that many young children who had learned the novel word “chromium”, still remembered part of its meaning six weeks later. Markson and Bloom (1997) showed that, in a pointing task, threeand four-year-old children performed well above chance after a month delay. One important notion regarding lexical learning and generalization is that young children are thought to be perfectly able to segregate a target referent from the scene it is embedded in and to associate it with its name. For example, the concept of fast mapping implies that children grasp an object (for instance) and associate it with a word, no matter the scene, the spatial context, in which the object is included. Later, the child is supposed to be able to recognize, name or designate the correct referent in novel contexts. It is also generally recognized that children are able to generalize the new word to new instances that differ from the original object according to various dimensions (Clark, 1993; Mervis, 1987; Smith, 1999) (even though there is much debate regarding the dimensions according to which children will spontaneously generalize). This view of novel name learning and generalization predicts that the name of an object should be recovered later despite variations in the characteristics of the referents and of the scenes in which it was embedded in the learning phase. The following experiments have several purposes. First, we assess the stability of performance across delays (immediate post-test, compared with a two-week delay). Following Markson and Bloom (1997), Bartlett and Carey (1978), we hypothesize that performance should be stable across delays. However, their results were obtained for a comprehension (pointing) task. In the same way, Childers and Tomasello (2002) assessed comprehension and naming at various intervals after training (immediate, one day and one week later) and found no effect of delay on both types of scores. A second purpose of the present experiments, is to study generalization of novel names, as a function of superficial characteristics, such as the scene in which the stimulus was embedded during the learning phase and its congruence (see methods) with the scene in which the stimulus is embedded at test, or such as perceptual differences between the training referent and novel instances introduced later. More generally, our central question is whether the context in which the association between a novel name (e.g. the word “tapir”) and a referent (the tapir) was “inserted” will influence future generalization tasks such as naming or pointing tasks. More specifically, we want to introduce memory factors in the question of novel word generalization. During lexical learning and generalization, children encounter objects belonging to the same category in various contexts. For example, a child plays with a new toy (e.g., a crane) and learns its name (“crane”) in one room and, later, might play with a new crane in another room or another house. The same is true for pictures of objects: children can see a cat in a book and learn its name, while being confronted with a different cat later in another book. Most lexical learning theories would assume that children spontaneously generalize a novel name to novel instances of the original referent, displayed in a new spatial setting if (i.e., a novel scene) (e.g., Mervis, 1987). In the same way, they do not consider the “delay” component of a lexical learning task as a central issue: in most experiments, one tests generalization immediately after a novel referent has been associated with a novel name and in situations in which the learning object remains in view (Mervis & Bertrand, 1994; Samuelson & Smith, 2000). Given the above evidence regarding delays (e.g., Childers & Tomasello, 2002) and the notion of fast mapping, memory factors do not seem to play any central role in lexical generalization. In other words, the implicit general hypothesis is that “context” parameters do not influence the encoding of the association between the word and the object and, thus, its later retrieval. By contrast, our contention is that memory factors might interact with generalization of novel names to novel instances especially when they are displayed in new scenes. Our reasoning is based on the encoding specificity hypothesis (Tulving & Thomson, 1973), according to which an event is stored in memory together with the spatial and temporal information associated with the target stimulus during encoding (e.g., the scene a stimulus is embedded in). Later recovery is facilitated when the cues encoded during learning are available at test in the sense that properties of effective retrieval cues are determined by the specific encoding operations performed by the system on the input (see Baddeley, 1997; Balsam & Tomie, 1985). In a lexical learning task, this view can be translated in the following terms: a child always learns a novel word for a particular instance of a category in a particular scene, which results in the encoding of retrieval cues that are specific to this learning setting. Later presentations of novel instances of the same category in new scenes should elicit, by definition, poorer retrieval cues than the retrieval cues provided by the original instance displayed in its original scene. This should result in a poorer recall of the stimulus name association. By contrast, if, as mentioned above, a novel word is spontaneously generalized to new instances of the same category even when they are displayed on new scenes, one should not predict any influence of these differences between training and recall situations. Note that our view has important consequences on the notion of undergeneralization which is quite common in early lexical learning. It is defined as a lexical use in which children extend a novel word to a subset of the referents to which the adults extend the same word (e.g., the word “dog” used for small dogs only). The common explanation of these undergeneralizations is conceptual: preschool children fail to extend novel words because they do not understand that the novel entities belong to the same category as the referents to which they already extend the word. Within our memory hypothesis, we want to suggest that some undergeneralizations might not be conceptual but might result from poorer retrieval cues available when novel referents and/or novel scene settings are introduced, compared with the retrieval cues available when old stimuli and scenes are displayed. In order to show that undergeneralization is not conceptually-based, one has to show that children extend novel words less well to referents they have never seen before than to the learning referents; while, at the same time, they give independent evidence that they understand that these novel stimuli belong to the same category as the learning stimuli. In our first experiment we compared performance for old referents (i.e., the ones shown in the training phase) and new referents displayed on their novel training scenes or on new test scenes at two delays: immediate and two weeks after training.