Cross-situational Learning From Ambiguous Egocentric Input Is a Continuous Process: Evidence Using the Human Simulation Paradigm

Recent laboratory experiments have shown that both infant and adult learners can acquire word-referent mappings using cross-situational statistics. The vast majority of the work on this topic has used unfamiliar objects presented on neutral backgrounds as the visual contexts for word learning. However, these laboratory contexts are much different than the real-world contexts in which learning occurs. Thus, the feasibility of generalizing cross-situational learning beyond the laboratory is in question. Adapting the Human Simulation Paradigm, we conducted a series of experiments examining cross-situational learning from children's egocentric videos captured during naturalistic play. Focusing on individually ambiguous naming moments that naturally occur during toy play, we asked how statistical learning unfolds in real time through accumulating cross-situational statistics in naturalistic contexts. We found that even when learning situations were individually ambiguous, learners’ performance gradually improved over time. This improvement was driven in part by learners’ use of partial knowledge acquired from previous learning situations, even when they had not yet discovered correct word-object mappings. These results suggest that word learning is a continuous process by means of real-time information integration.     

Detailed behavioral analysis as a window into cross-situational word learning

Recent research has demonstrated that word learners can determine word-referent mappings by tracking co-occurrences across multiple ambiguous naming events. The current study addresses the mechanisms underlying this capacity to learn words cross-situationally. This replication and extension of Yu and Smith (2007) investigates the factors influencing both successful cross-situational word learning and mis-mappings. Item analysis and error patterns revealed that the co-occurrence structure of the learning environment as well as the context of the testing environment jointly affected learning across observations. Learners also adopted an exclusion strategy, which contributed conjointly with statistical tracking to performance. Implications for our understanding of the processes underlying cross-situational word learning are discussed.     

Exploring the robustness of cross-situational learning under Zipfian distributions

Cross-situational learning has recently gained attention as a plausible candidate for the mechanism that underlies the learning of word-meaning mappings. In a recent study, Blythe and colleagues have studied how many trials are theoretically required to learn a human-sized lexicon using cross-situational learning. They show that the level of referential uncertainty exposed to learners could be relatively large. However, one of the assumptions they made in designing their mathematical model is questionable. Although they rightfully assumed that words are distributed according to Zipf's law, they applied a uniform distribution of meanings. In this article, Zipf's law is also applied to the distribution of meanings, and it is shown that under this condition, cross-situational learning can only be plausible when referential uncertainty is sufficiently small. It is concluded that cross-situational learning is a plausible learning mechanism but needs to be guided by heuristics that aid word learners with reducing referential uncertainty.     

Learning times for large lexicons through cross-situational learning

Cross-situational learning is a mechanism for learning the meaning of words across multiple exposures, despite exposure-by-exposure uncertainty as to a word's true meaning. Doubts have been expressed regarding the plausibility of cross-situational learning as a mechanism for learning human-scale lexicons in reasonable timescales under the levels of referential uncertainty likely to confront real word learners. We demonstrate mathematically that cross-situational learning facilitates the acquisition of large vocabularies despite significant levels of referential uncertainty at each exposure, and we provide estimates of lexicon learning times for several cross-situational learning strategies. This model suggests that cross-situational word learning cannot be ruled out on the basis that it predicts unreasonably long lexicon learning times. More generally, these results indicate that there is no necessary link between the ability to learn individual words rapidly and the capacity to acquire a large lexicon.     

2.5-year-olds use cross-situational consistency to learn verbs under referential uncertainty

Recent evidence shows that children can use cross-situational statistics to learn new object labels under referential ambiguity (e.g., Smith & Yu, 2008). Such evidence has been interpreted as support for proposals that statistical information about word-referent co-occurrence plays a powerful role in word learning. But object labels represent only a fraction of the vocabulary children acquire, and arguably represent the simplest case of word learning based on observations of world scenes. Here we extended the study of cross-situational word learning to a new segment of the vocabulary, action verbs, to permit a stronger test of the role of statistical information in word learning. In two experiments, on each trial 2.5-year-olds encountered two novel intransitive (e.g., "She's pimming!"; Experiment 1) or transitive verbs (e.g., "She's pimming her toy!"; Experiment 2) while viewing two action events. The consistency with which each verb accompanied each action provided the only source of information about the intended referent of each verb. The 2.5-year-olds used cross-situational consistency in verb learning, but also showed significant limits on their ability to do so as the sentences and scenes became slightly more complex. These findings help to define the role of cross-situational observation in word learning.     

Looking in the wrong direction correlates with more accurate word learning

Previous research on lexical development has aimed to identify the factors that enable accurate initial word-referent mappings based on the assumption that the accuracy of initial word-referent associations is critical for word learning. The present study challenges this assumption. Adult English speakers learned an artificial language within a cross-situational learning paradigm. Visual fixation data were used to assess the direction of visual attention. Participants whose longest fixations in the initial trials fell more often on distracter images performed significantly better at test than participants whose longest fixations fell more often on referent images. Thus, inaccurate initial word-referent mappings may actually benefit learning.     

Fine-grained sensitivity to statistical information in adult word learning

A language learner trying to acquire a new word must often sift through many potential relations between particular words and their possible meanings. In principle, statistical information about the distribution of those mappings could serve as one important source of data, but little is known about whether learners can in fact track multiple word-referent mappings, and, if they do, the precision with which they can represent those statistics. To test this, two experiments contrasted a pair of possibilities: that learners encode the fine-grained statistics of mappings in the input - both high- and low-frequency mappings - or, alternatively, that only high frequency mappings are represented. Participants were briefly trained on novel word-novel object pairs combined with varying frequencies: some objects were paired with one word, other objects with multiple words with differing frequencies (ranging from 10% to 80%). Results showed that participants were exquisitely sensitive to very small statistical differences in mappings. The second experiment showed that word learners' representation of low frequency mappings is modulated as a function of the variability in the environment. Implications for Mutual Exclusivity and Bayesian accounts of word learning are discussed.     

Integrating constraints for learning word-referent mappings

Learning word-referent mappings is complex because the word and its referent tend to co-occur with multiple other words and potential referents. Such complexity has led to proposals for a host of constraints on learning, though how these constraints may interact has not yet been investigated in detail. In this paper, we investigated interactions between word co-occurrence constraints and cross-situational statistics in word learning. Analyses of child-directed speech revealed that when both object-referring and non-referring words occurred in the utterance, referring words were more likely to be preceded by a determiner than when the utterance contained only referring words. In a word learning study containing both referring and non-referring words, learning was facilitated when non-referring words contributed grammatical constraints analogous to determiners. The complexity of multi-word utterances provides an opportunity for co-occurrence constraints to contribute to word-referent mapping, and the learning mechanism is able to integrate these multiple sources of information.     

What Is the Buzz About Iconicity? How Iconicity in Caregiver Speech Supports Children's Word Learning

One cue that may facilitate children's word learning is iconicity, or the correspondence between a word's form and meaning. Some have even proposed that iconicity in the early lexicon may serve to help children learn how to learn words, supporting the acquisition of even noniconic, or arbitrary, word–referent associations. However, this proposal remains untested. Here, we investigate the iconicity of caregivers’ speech to young children during a naturalistic free-play session with novel stimuli and ask whether the iconicity of caregivers’ speech facilitates children's learning of the noniconic novel names of those stimuli. Thirty-four 1.5-2-year-olds (19 girls; half monolingual English learners and half bilingual English-Spanish learners) participated in a naturalistic free-play task with their caregivers followed by a test of word-referent retention. We found that caregivers’ use of iconicity, particularly in utterances in which they named the novel stimuli, was associated with the likelihood that children learned that novel name. This result held even when controlling for other factors associated with word learning, such as the concreteness and frequency of words in caregiver speech. Together, the results demonstrate that iconicity not only can serve to help children identify the referent of novel words (as in previous research) but can also support their ability to retain even noniconic word-referent mappings.     

Propose but verify: Fast mapping meets cross-situational word learning

We report three eyetracking experiments that examine the learning procedure used by adults as they pair novel words and visually presented referents over a sequence of referentially ambiguous trials. Successful learning under such conditions has been argued to be the product of a learning procedure in which participants provisionally pair each novel word with several possible referents and use a statistical-associative learning mechanism to gradually converge on a single mapping across learning instances [e.g., Yu, C., & Smith, L. B. (2007). Rapid word learning under uncertainty via cross-situational statistics. Psychological Science, 18(5), 414–420]. We argue here that successful learning in this setting is instead the product of a one-trial procedure in which a single hypothesized word-referent pairing is retained across learning instances, abandoned only if the subsequent instance fails to confirm the pairing – more a ‘fast mapping’ procedure than a gradual statistical one. We provide experimental evidence for this propose-but-verify learning procedure via three experiments in which adult participants attempted to learn the meanings of nonce words cross-situationally under varying degrees of referential uncertainty. The findings, using both explicit (referent selection) and implicit (eye movement) measures, show that even in these artificial learning contexts, which are far simpler than those encountered by a language learner in a natural environment, participants do not retain multiple meaning hypotheses across learning instances. As we discuss, these findings challenge ‘gradualist’ accounts of word learning and are consistent with the known rapid course of vocabulary learning in a first language.     

The role of partial knowledge in statistical word learning

A critical question about the nature of human learning is whether it is an all-or-none or a gradual, accumulative process. Associative and statistical theories of word learning rely critically on the later assumption: that the process of learning a word’s meaning unfolds over time. That is, learning the correct referent for a word involves the accumulation of partial knowledge across multiple instances. Some theories also make an even stronger claim: Partial knowledge of one word–object mapping can speed up the acquisition of other word–object mappings. We present three experiments that test and verify these claims by exposing learners to two consecutive blocks of cross-situational learning, in which half of the words and objects in the second block were those that participants failed to learn in Block 1. In line with an accumulative account, Re-exposure to these mis-mapped items accelerated the acquisition of both previously experienced mappings and wholly new word–object mappings. But how does partial knowledge of some words speed the acquisition of others? We consider two hypotheses. First, partial knowledge of a word could reduce the amount of information required for it to reach threshold, and the supra-threshold mapping could subsequently aid in the acquisition of new mappings. Alternatively, partial knowledge of a word’s meaning could be useful for disambiguating the meanings of other words even before the threshold of learning is reached. We construct and compare computational models embodying each of these hypotheses and show that the latter provides a better explanation of the empirical data.     

Mapping Word to World in ASL: Evidence from a Human Simulation Paradigm

Across languages, children map words to meaning with great efficiency, despite a seemingly unconstrained space of potential mappings. The literature on how children do this is primarily limited to spoken language. This leaves a gap in our understanding of sign language acquisition, because several of the hypothesized mechanisms that children use are visual (e.g., visual attention to the referent), and sign languages are perceived in the visual modality. Here, we used the Human Simulation Paradigm in American Sign Language (ASL) to determine potential cues to word learning. Sign-naïve adult participants viewed video clips of parent–child interactions in ASL, and at a designated point, had to guess what ASL sign the parent produced. Across two studies, we demonstrate that referential clarity in ASL interactions is characterized by access to information about word class and referent presence (for verbs), similarly to spoken language. Unlike spoken language, iconicity is a cue to word meaning in ASL, although this is not always a fruitful cue. We also present evidence that verbs are highlighted well in the input, relative to spoken English. The results shed light on both similarities and differences in the information that learners may have access to in acquiring signed versus spoken languages.     

Infants rapidly learn word-referent mappings via cross-situational statistics

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.     

The dynamic functions of social cues during children's word learning

Children learn words in a social environment, facilitated in part by social cues from caregivers, such as eye-gaze and gesture. A common assumption is that social cues convey either perceptual or social information, depending on the age of the child. In this review of research on word learning and social cues during early childhood, we propose that (1) the functions of social cues are not categorically perceptual or social, and (2) social cues support word learning in four interdependent ways: by helping children to orient attention, extract relevant information, disambiguate referents, and understand others' referential intent. We conclude with specific recommendations for theory-building and suggest that the dynamic and complex functions of social cues need to be accounted for in any complete theory of word learning.     

Rapid word learning under uncertainty via cross-situational statistics

There are an infinite number of possible word-to-word pairings in naturalistic learning environments. Previous proposals to solve this mapping problem have focused on linguistic, social, representational, and attentional constraints at a single moment. This article discusses a cross-situational learning strategy based on computing distributional statistics across words, across referents, and, most important, across the co-occurrences of words and referents at multiple moments. We briefly exposed adults to a set of trials that each contained multiple spoken words and multiple pictures of individual objects; no information about word-picture correspondences was given within a trial. Nonetheless, over trials, subjects learned the word-picture mappings through cross-trial statistical relations. Different learning conditions varied the degree of within-trial reference uncertainty, the number of trials, and the length of trials. Overall, the remarkable performance of learners in various learning conditions suggests that they calculate cross-trial statistics with sufficient fidelity and by doing so rapidly learn word-referent pairs even in highly ambiguous learning contexts.     

Cross‐Situational Learning: An Experimental Study of Word‐Learning Mechanisms

Cross‐situational learning is a mechanism for learning the meaning of words across multiple exposures, despite exposure‐by‐exposure uncertainty as to the word's true meaning. We present experimental evidence showing that humans learn words effectively using cross‐situational learning, even at high levels of referential uncertainty. Both overall success rates and the time taken to learn words are affected by the degree of referential uncertainty, with greater referential uncertainty leading to less reliable, slower learning. Words are also learned less successfully and more slowly if they are presented interleaved with occurrences of other words, although this effect is relatively weak. We present additional analyses of participants’ trial‐by‐trial behavior showing that participants make use of various cross‐situational learning strategies, depending on the difficulty of the word‐learning task. When referential uncertainty is low, participants generally apply a rigorous eliminative approach to cross‐situational learning. When referential uncertainty is high, or exposures to different words are interleaved, participants apply a frequentist approximation to this eliminative approach. We further suggest that these two ways of exploiting cross‐situational information reside on a continuum of learning strategies, underpinned by a single simple associative learning mechanism.     

Beyond naïve cue combination: salience and social cues in early word learning

Children learn their earliest words through social interaction, but it is unknown how much they rely on social information. Some theories argue that word learning is fundamentally social from its outset, with even the youngest infants understanding intentions and using them to infer a social partner's target of reference. In contrast, other theories argue that early word learning is largely a perceptual process in which young children map words onto salient objects. One way of unifying these accounts is to model word learning as weighted cue combination, in which children attend to many potential cues to reference, but only gradually learn the correct weight to assign each cue. We tested four predictions of this kind of naïve cue combination account, using an eye‐tracking paradigm that combines social word teaching and two‐alternative forced‐choice testing. None of the predictions were supported. We thus propose an alternative unifying account: children are sensitive to social information early, but their ability to gather and deploy this information is constrained by domain‐general cognitive processes. Developmental changes in children's use of social cues emerge not from learning the predictive power of social cues, but from the gradual development of attention, memory, and speed of information processing.     

Two‐year‐old children preferentially transmit simple actions but not pedagogically demonstrated actions

Children are sensitive to both social and non‐social aspects of the learning environment. Among social cues, pedagogical communication has been shown to not only play a role in children's learning, but also in their own active transmission of knowledge. Vredenburgh, Kushnir and Casasola, Developmental Science, 2015, 18, 645 showed that 2‐year‐olds are more likely to demonstrate an action to a naive adult after learning it in a pedagogical than in a non‐pedagogical context. This finding was interpreted as evidence that pedagogically transmitted information has a special status as culturally relevant. Here we test the limits of this claim by setting it in contrast with an explanation in which the relevance of information is the outcome of multiple interacting social (e.g., pedagogical demonstration) and non‐social properties (e.g., action complexity). To test these competing hypotheses, we varied both pedagogical cues and action complexity in an information transmission paradigm with 2‐year‐old children. In Experiment 1, children preferentially transmitted simple non‐pedagogically demonstrated actions over pedagogically demonstrated more complex actions. In Experiment 2, when both actions were matched for complexity, we found no evidence of preferential transmission of pedagogically demonstrated actions. We discuss possible reasons for the discrepancy between our results and previous literature showing an effect of pedagogical cues on cultural transmission, and conclude that our results are compatible with the view that pedagogical and other cues interact, but incompatible with the theory of a privileged role for pedagogical cues.     

The use of social and salience cues in early word learning

This article explores young infants' ability to learn new words in situations providing tightly controlled social and salience cues to their reference. Four experiments investigated whether, given two potential referents, 15-month-olds would attach novel labels to (a) an image toward which a digital recording of a face turned and gazed, (b) a moving image versus a stationary image, (c) a moving image toward which the face gazed, and (d) a gazed-on image versus a moving image. Infants successfully used the recorded gaze cue to form new word-referent associations and also showed learning in the salience condition. However, their behavior in the salience condition and in the experiments that followed suggests that, rather than basing their judgments of the words' reference on the mere presence or absence of the referent's motion, infants were strongly biased to attend to the consistency with which potential referents moved when a word was heard.     

Phonological and semantic processes influence beginning readers' ability to learn to read words

Children (4 to 6 years of age) were taught to associate printed 3- or 4-letter abbreviations, or cues, with spoken words (e.g., bfr for beaver). All but 1 of the letters in the cue corresponded to phonemes in the spoken target word. Two types of cues were constructed: phonetic cues, in which the medial letter was phonetically similar to the target word, and control cues, in which the central phoneme was phonetically dissimilar. In Experiment 1, children learned the phonetic cues better than the control cues, and learning correlated with measures of phonological skill and knowledge of the meanings of the words taught. In Experiment 2, the target words differed on a semantic variable-imageability-and learning was influenced by both the phonetic properties of the cue and the imageability of the words used.