Rapid fast-mapping abilities in 2-year-olds

Abstract

Learning a new word consists of two primary tasks that have often been conflated into a single process: referent selection, in which a child must determine the correct referent of a novel label, and referent retention, which is the ability to store this newly formed label–object mapping in memory for later use. In addition, children must be capable of performing these tasks rapidly and repeatedly as they are frequently exposed to novel words during the course of natural conversation. Here we used a preferential pointing task to investigate 2-year-olds’ (N = 72) ability to infer the referent of a novel noun from a single ambiguous exposure and their ability to retain this mapping over time. Children were asked to identify the referent of a novel label on six critical trials distributed throughout the course of a 10-min study involving many familiar and novel objects. On these critical trials, images of a known object and a novel object (e.g., a ball and a nameless artifact constructed in the laboratory) appeared on two computer screens and a voice asked children to “point at the _____ [e.g., glark].” Following label onset, children were allowed only 3 s during which to infer the correct referent, point at it, and potentially store this new word–object mapping. In a final posttest trial, all previously labeled novel objects appeared and children were asked to point to one of them (e.g., “Can you find the glark?”). To succeed, children needed to have initially mapped the novel labels correctly and retained these mappings over the course of the study. Despite the difficult demands of the current task, children successfully identified the target object on the retention trial. We conclude that 2-year-olds are able to fast map novel nouns during a brief single exposure under ambiguous labeling conditions.

Introduction

The study of fast mapping focuses on what children learn about a word after minimal exposure to a new label (for reviews, see Jaswal and Markman, 2001, Wilkinson and Mazzitelli, 2003, Woodward and Markman, 1998). The term unambiguous or ostensive refers to a naming act in which external cues (e.g., overt linguistic cues, cues from communicative intent) that direct children’s attention to the correct referent are provided. Although behavioral cues carry with them their own challenges of ambiguity, experimenters have successfully elicited fast mapping by overtly drawing children’s attention to the referent via pointing (Baldwin, 1993a, Leung and Rheingold, 1981), eye gaze (Baldwin, 1991, Baldwin, 1993b, Dunham et al., 1993), or an explicit linguistic contrast (e.g., “Bring me the chromium tray, not the red one; I want the chromium one”) (Carey & Bartlett, 1978). In the most extreme case, the correct referent is the only object present, making the referent of the new word quite clear (Au and Glusman, 1990, Baldwin et al., 1996, Booth and Waxman, 2002, Dickinson, 1984, Markson and Bloom, 1997, Waxman and Booth, 2000).

Recent work has extended these demonstrations of fast mapping to more ambiguous labeling acts, showing that 2-year-olds can learn as much about a new word from an indirect exposure as from an act of ostensive labeling (Jaswal & Markman, 2001; for related results, see Golinkoff et al., 1992, Mervis and Bertrand, 1994, Rice, 1990, Vincent-Smith et al., 1974, Wilkinson and Mazzitelli, 2003). Work on fast mapping has also shown that children can retain a newly learned word for a significant amount of time following the initial encounter. In the original demonstration, Carey and Bartlett (1978) showed that children remember some semantic information about a novel label more than 1 week after a single encounter with it. Markson and Bloom (1997) extended this result and showed successful retention at delays of 1 month after the initial exposure to a single new word.

Although these studies have been integral to our understanding of fast mapping, many questions remain. For example, the connection between identifying the correct referent during learning (referent selection) and reidentifying it at test (referent retention) has received less attention. One recent contribution is a study by Horst and Samuelson (2008) in which 24-month-olds were exposed to eight novel object–label mappings during a referent selection task and retention for these mappings was tested after a 5-min delay. The authors found that although children succeeded during the initial referent selection trials, they failed to correctly reidentify the target during the delayed retention test trial. The difficulty of transitioning from referent selection to referent retention can be further complicated because children may hear multiple new words in quick succession. This challenge may be ameliorated with multiple exposures to a new word across trials (Mather & Plunkett, 2009) or multiple naming acts in a natural conversation.

In the most common experimental designs, children learn only a few object names or only one object name (Baldwin et al., 1996, Behrend et al., 2001, Dollaghan, 1985, Golinkoff et al., 1992), the novel label may be repeated many times (Au and Glusman, 1990, Markman et al., 2003, Woodward et al., 1994), and the object being referred to is clearly indicated (Carey and Bartlett, 1978, Markson and Bloom, 1997, Mervis et al., 1994). If children rely on fast mapping to rapidly acquire new words, then they must be able to demonstrate successful learning under a wide range of conditions. A manipulation that has yet to be tested in a single experiment is whether children can use fast mapping to learn multiple novel words when each object and label is presented only once under ambiguous and time-constrained conditions (but see Horst & Samuelson, 2008).

We had two goals for our experiment: (a) to test the fast-mapping abilities of 2-year-olds under conditions that are challenging on a number of dimensions and (b) to investigate whether such conditions allow children to succeed at both the initial mapping of a novel label to a novel object (referent selection) and the retention of this mapping for use at a later time (referent retention). We presented children with six ambiguous referent selection novel label trials over the course of the study. On these trials, children saw a familiar object (e.g., a ball) and a novel object, and a voice on a computer asked them to “point at the _____ [e.g., glark].” Including the four practice trials, children saw 38 familiar objects and 12 novel objects, they heard 22 familiar labels and 6 novel labels, and each label was uttered only once in an ambiguous context over the course of a 10-min experiment.¹ We tested retention for the novel labels by presenting all six previously labeled novel objects and probing retention for one of them in a single posttest retention trial.