Infants' First Words are not Phonetically Specified: Own Name Recognition in British English‐Learning 5‐Month‐Olds

By the end of their first year of life, infants’ representations of familiar words contain phonetic detail; yet little is known about the nature of these representations at the very beginning of word learning. Bouchon et al. ( 2015 ) showed that French‐learning 5‐month‐olds could detect a vowel change in their own name and not a consonant change, but also that infants reacted to the acoustic distance between vowels. Here, we tested British English‐learning 5‐month‐olds in a similar study to examine whether the acoustic/phonological characteristics of the native language shape the nature of the acoustic/phonetic cues that infants pay attention to. In the first experiment, British English‐learning infants failed to recognize their own name compared to a mispronunciation of initial consonant (e.g., Molly versus Nolly) or vowel (e.g., April versus Ipril). Yet in the second experiment, they did so when the contrasted name was phonetically dissimilar (e.g., Sophie versus Amber). Differences in phoneme category (stops versus continuants) between the correct consonant versus the incorrect one significantly predicted infants’ own name recognition in the first experiment. Altogether, these data suggest that infants might enter into a phonetic mode of processing through different paths depending on the acoustic characteristics of their native language.     

Infants' Ability to Learn Phonetically Similar Words: Effects of Age and Vocabulary Size

What do novice word learners know about the sound of words? Word‐learning tasks suggest that young infants (14 months old) confuse similar‐sounding words, whereas mispronunciation detection tasks suggest that slightly older infants (18–24 months old) correctly distinguish similar words. Here we explore whether the difficulty at 14 months stems from infants' novice status as word learners or whether it is inherent in the task demands of learning new words. Results from 3 experiments support a developmental explanation. In Experiment 1, infants of 20 months learned to pair 2 phonetically similar words to 2 different objects under precisely the same conditions that infants of 14 months (Experiment 2) failed. In Experiment 3, infants of 17 months showed intermediate, but still successful, performance in the task. Vocabulary size predicted word‐learning performance, but only in the younger, less experienced word learners. The implications of these results for theories of word learning and lexical representation are discussed.     

Language Experience Shapes the Development of the Mutual Exclusivity Bias

Halberda (2003) demonstrated that 17‐month‐old infants, but not 14‐ or 16‐month‐olds, use a strategy known as mutual exclusivity (ME) to identify the meanings of new words. When 17‐month‐olds were presented with a novel word in an intermodal preferential looking task, they preferentially fixated a novel object over an object for which they already had a name. We explored whether the development of this word‐learning strategy is driven by children’s experience of hearing only one name for each referent in their environment by comparing the behavior of infants from monolingual and bilingual homes. Monolingual infants aged 17–22 months showed clear evidence of using an ME strategy, in that they preferentially fixated the novel object when they were asked to “look at the dax.” Bilingual infants of the same age and vocabulary size failed to show a similar pattern of behavior. We suggest that children who are raised with more than one language fail to develop an ME strategy in parallel with monolingual infants because development of the bias is a consequence of the monolingual child’s everyday experiences with words.     

The Use of Pitch Accent in Word–Object Association by Monolingual Japanese Infants

This study investigated the lexical use of Japanese pitch accent in Japanese‐learning infants. A word–object association task revealed that 18‐month‐old infants succeeded in learning the associations between two nonsense objects paired with two nonsense words minimally distinguished by pitch pattern (Experiment 1). In contrast, 14‐month‐old infants failed (Experiment 2). Eighteen‐month‐old infants succeeded even for sounds that contained only the prosodic information (Experiment 3). However, a subsequent experiment revealed that 14‐month‐old infants succeeded in an easier single word–object task using pitch contrast (Experiment 4). These findings indicate that pitch pattern information is robustly available to 18‐month‐old Japanese monolingual infants in a minimal pair word‐learning situation, but only partially accessible in the same context for 14‐month‐old infants.     

Is a Bird an Apple? The Effect of Speaker Labeling Accuracy on Infants' Word Learning,Imitation, and Helping Behaviors

This study examined infants' sensitivity to a speaker's verbal accuracy and whether the reliability of the speaker had an effect on their selective trust. Forty‐nine 18‐month‐old infants were exposed to a speaker who either accurately or inaccurately labeled familiar objects. Subsequently, the speaker administered a series of tasks in which infants had an opportunity to: learn a novel word, imitate the speaker's “irrational” actions, and help the speaker obtain an out‐of‐reach object. In contrast to infants in the accurate (reliable) condition, those in the inaccurate (unreliable) condition performed more poorly on a word‐learning task and were less likely to imitate. All infants demonstrated high rates of instrumental helping behavior. These results are the first to demonstrate that infants as young as 18 months of age cannot only detect a speaker's verbal inaccuracy but also use this information to attenuate their word recognition and learning of novel actions.     

Vois‐Tu Le Kem? Do You See the Bos? Foreign Word Learning at 14 Months

How easily can infants regularly exposed to only one language begin to acquire a second one? In three experiments, we tested 14‐month‐old English and French monolingual infants’ ability to learn words presented in foreign language sentence frames. Infants were trained on two novel word‐object pairings and then tested using a preferential looking task. Word forms were phonetically and phonotactically legal in both languages, and cross‐spliced across conditions, so only the sentence frames established the word as native or foreign. In Experiment 1, infants were taught one native and one foreign word and successfully learned both. In Experiment 2 and 3, infants were taught two foreign words, but only showed successful learning of the first word they encountered. These results demonstrate that infants can successfully learn words embedded in foreign language sentences, but this is more challenging than native word learning. More broadly, they show that the sentential context of a novel word, and not just the word form itself, influences infants’ early word learning.     

Learning While Babbling: Prelinguistic Object‐Directed Vocalizations Indicate a Readiness to Learn

Two studies illustrate the functional significance of a new category of prelinguistic vocalizing—object‐directed vocalizations (ODVs)—and show that these sounds are connected to learning about words and objects. Experiment 1 tested 12‐month‐old infants’ perceptual learning of objects that elicited ODVs. Fourteen infants’ vocalizations were recorded as they explored novel objects. Infants learned visual features of objects that elicited the most ODVs but not of objects that elicited the fewest vocalizations. Experiment 2 assessed the role of ODVs in learning word–object associations. Forty infants aged 11.5 months played with a novel object and received a label either contingently on an ODV or on a look alone. Only infants who received labels in response to an ODV learned the association. Taken together, the findings suggest that infants’ ODVs signal a state of attention that facilitates learning.     

Word Level Stress and Lexical Processing in 17‐Month‐Old Infants

Detailed representations enable infants to distinguish words from one another and more easily recognize new words. We examined whether 17‐month‐old infants encode word stress in their familiar word representations. In Experiment 1, infants were presented with pairs of familiar objects while hearing a target label either properly pronounced with the correct stress (e.g., baby /’be?bi/) or mis‐pronounced with the incorrect stress pattern (e.g., baby /be?’bi/). Infants mapped both the correctly stressed and mis‐stressed labels to the target objects; however, they were slower to fixate the target when hearing the mis‐stressed label. In Experiment 2, we examined whether infants appreciate that stress has a nonproductive role in English (i.e., altering the stress of a word does not typically signal a change in word meaning) by presenting infants with a familiar object paired with a novel object while hearing either correctly stressed or mis‐stressed familiar words (Experiment 2). Here, infants mapped the correctly stressed label to the familiar object but did not map the mis‐stressed label reliably to either the target or distractor objects. These findings suggest that word stress impacts the processing of familiar words, and infants have burgeoning knowledge that altering the stress pattern of a familiar word does not reliably signal a new referent.     

Fast Mapping but Poor Retention by 24‐Month‐Old Infants

Four experiments explored the processes that bridge between referent selection and word learning. Twenty‐four‐month‐old infants were presented with several novel names during a referent selection task that included both familiar and novel objects and tested for retention after a 5‐min delay. The 5‐min delay ensured that word learning was based on retrieval from long‐term memory. Moreover, the relative familiarity of objects used during the retention test was explicitly controlled. Across experiments, infants were excellent at referent selection, but very poor at retention. Although the highly controlled retention test was clearly challenging, infants were able to demonstrate retention of the first 4 novel names presented in the session when referent selection was augmented with ostensive naming. These results suggest that fast mapping is robust for reference selection but might be more transient than previously reported for lexical retention. The relations between reference selection and retention are discussed in terms of competitive processes on 2 timescales: competition among objects on individual referent selection trials and competition among multiple novel name–object mappings made across an experimental session.     

Functional Parallelism of Detailed and Rough Speech Processing at the End of Infancy

Although realization of the same speech sound is far from being consistent across different contexts, speech recognition has to rely on phonetic detail in order to detect words. So far, it appeared that young infants cannot avoid noticing subtle speech sound variation whenever it occurs. Only later on, they are able to tolerate speech sound variation in some word recognition tasks. Here, we test whether this ability is associated with the time infants start storing their first word forms. We recorded event‐related potentials (ERPs) in a priming paradigm. German words (targets) followed syllables (primes) with a different amount of phoneme overlap. We tested infants at three, six, and nine months after birth. ERPs reflected sensitivity to prime‐target variation in a single phoneme in three‐month‐olds, tolerance to this in six‐month‐olds, and both processing aspects in nine‐month‐olds. Our findings reveal individual developmental priorities for different aspects of speech processing, with very detailed speech processing dominating at around 3 months, rough processing dominating at around half a year after birth, and an architecture of parallel rough and detailed processing at around 9 months. Functional parallelism at the end of infancy might explain the heterogeneous pattern of results regarding the degree of acoustic detail that toddlers appear to consider at different ages and across different paradigms.     

Beneficial effects of the mother's voice on infants’ novel word learning

The maternal voice appears to have a special role in infants’ language processing. The current eye‐tracking study investigated whether 24‐month‐olds (n = 149) learn novel words easier while listening to their mother's voice compared to hearing unfamiliar speakers. Our results show that maternal speech facilitates the formation of new word–object mappings across two different learning settings: a live setting in which infants are taught by their own mother or the experimenter, and a prerecorded setting in which infants hear the voice of either their own or another mother through loudspeakers. Furthermore, this study explored whether infants’ pointing gestures and novel word productions over the course of the word learning task serve as meaningful indexes of word learning behavior. Infants who repeated more target words also showed a larger learning effect in their looking behavior. Thus, maternal speech and infants’ willingness to repeat novel words are positively linked with novel word learning.     

The First Slow Step: Differential Effects of Object and Word-Form Familiarization on Retention of Fast-Mapped Words

Recent research demonstrated that although twenty-four month-old infants do well on the initial pairing of a novel word and novel object in fast-mapping tasks, they are unable to retain the mapping after a five-minute delay. The current study examines the role of familiarity with the objects and words on infants' ability to bridge between the initial fast mapping of a name and object, and later retention in the service of slow mapping. Twenty-four-month-old infants were familiarized with either novel objects or novel names prior to the referent selection portion of a fast-mapping task. When familiarized with the novel objects, infants retained the novel mapping after a delay, but not when familiarized with the novel words. This suggests familiarity with the object versus the word form leads to differential encoding of the name-object link. We discuss the implications of this finding for subsequent slow mapping.     

Phonotactic Constraints on Infant Word Learning

How do infants use their knowledge of native language sound patterns when learning words? There is ample evidence of infants’ precocious acquisition of native language sound structure during the first year of life, but much less evidence concerning how they apply this knowledge to the task of associating sounds with meanings in word learning. To address this question, 18‐month‐olds were presented with two phonotactically legal object labels (containing sound sequences that occur frequently in English) or two phonotactically illegal object labels (containing sound sequences that never occur in English), paired with novel objects. Infants were then tested using a looking‐while‐listening measure. The results revealed that infants looked at the correct objects after hearing the legal labels, but not the illegal labels. Furthermore, vocabulary size was related to performance. Infants with larger receptive vocabularies displayed greater differences between learning of legal and illegal labels than infants with smaller vocabularies. These findings provide evidence that infants’ knowledge of native language sound patterns influences their word learning.     

Distributional Phonetic Learning at 10 Months of Age

Infant phonetic perception reorganizes in accordance with the native language by 10 months of age. One mechanism that may underlie this perceptual change is distributional learning, a statistical analysis of the distributional frequency of speech sounds. Previous distributional learning studies have tested infants of 6–8 months, an age at which native phonetic categories have not yet developed. Here, three experiments test infants of 10 months to help illuminate perceptual ability following perceptual reorganization. English‐learning infants did not change discrimination in response to nonnative speech sound distributions from either a voicing distinction (Experiment 1) or a place‐of‐articulation distinction (Experiment 2). In Experiment 3, familiarization to the place‐of‐articulation distinction was doubled to increase the amount of exposure, and in this case infants began discriminating the sounds. These results extend the processes of distributional learning to a new phonetic contrast, and reveal that at 10 months of age, distributional phonetic learning remains effective, but is more difficult than before perceptual reorganization.     

14‐Month‐olds anticipate others’ actions based on their belief about an object's identity

Past research has accumulated evidence regarding infants’ false‐belief understanding, measuring their gaze patterns or active helping behaviors. However, the underlying mechanisms are still debated, specifically, whether young infants can compute that others represent the world under a certain aspect. Such performance requires holding in mind two representations about the same object simultaneously and attributing only one to another person. While 14‐month‐olds can encode an object under different aspects when forming first‐person representations, it is unclear whether infants at this very age could also predict others’ behavior based on their beliefs about an object's identity. Here, we investigate this question in a novel eye‐tracking‐based unexpected‐identity task. We measured 14‐month‐olds’ anticipatory looks combined with their looking time, using a violation‐of‐expectation paradigm. Results show that 14‐month‐olds look longer to an actor's reach that is incongruent with her false belief about the identity of an object compared to a congruent reach. Furthermore, infants correctly anticipated the actor's reach based on her false belief. Thus, as soon as infants represent dual identities they can integrate them in belief attributions and use them for consequent behavioral predictions. Such data provide evidence for the flexibility of false‐belief attributions and support proposals arguing for infants’ rich theory‐of‐mind abilities.     

A meta-analysis of infants’ word-form recognition

Recognizing word forms is an important step on infants’ way toward mastering their native language. The present study takes a meta-analytic approach to assess overarching questions on the literature of early word-form recognition. Specifically, we investigated the extent to which there is cross-linguistic evidence for an early recognition lexicon, and how it may be influenced by infant age, language background, and familiarity of the selected stimuli (approximated by parent-reported word knowledge). Our meta-analysis—with open data access on metalab.stanford.edu—was based on 32 experiments in 16 different published or unpublished studies on infants 5–15 months of age. We found an overall significant effect of word-form familiarity on infants’ responses. This effect increased with age and was higher for infants learning Romance languages than other languages. We further found that younger, but not older, infants showed higher effect sizes for more familiar word lists. These insights should help researchers plan future studies on word-form recognition.     

Can 18‐Month‐Old Infants Learn Words by Listening In on Conversations?

Previous research has shown that children as young as 2 can learn words from 3rd‐party conversations (Akhtar, Jipson, & Callanan, 2001). The focus of this study was to determine whether younger infants could learn a new word through overhearing. Novel object labels were introduced to 18‐month‐old infants in 1 of 2 conditions: directly by an experimenter or in the context of overhearing the experimenter use the word while interacting with another adult. The findings suggest that, when memory demands are not too high, 18‐month‐old infants can learn words through overhearing.     

Nineteen‐Month‐Olds' Understanding of the Conventionality of Object Labels Versus Desires

We assessed 19‐month‐olds' appreciation of the conventional nature of object labels versus desires. Infants played a finding game with an experimenter who stated her intention to find the referent of a novel word (word group), to find an object she wanted (desire group), or simply to look in a box (control group). A 2nd experimenter then administered a comprehension task to assess infants' tendency to extend information to a 2nd person who was not present at the time of learning. Results indicate that infants chose the target object when the 2nd experimenter asked for the referent of the novel label but not when she requested the referent of her desire. These findings demonstrate that 19‐month‐olds understand that words are conventional, but desires are not.     

Attention to Maternal Multimodal Naming by 6‐ to 8‐Month‐Old Infants and Learning of Word–Object Relations

We examined whether mothers' use of temporal synchrony between spoken words and moving objects, and infants' attention to object naming, predict infants' learning of word–object relations. Following 5 min of free play, 24 mothers taught their 6‐ to 8‐month‐olds the names of 2 toy objects, Gow and Chi, during a 3‐min play episode. Infants were then tested for their word mapping. The videotaped episodes were coded for mothers' object naming and infants' attention to different naming types. Results indicated that mothers' use of temporal synchrony and infants' attention during play covaried with infants' word‐mapping ability. Specifically, infants who switched eye gaze from mother to object most frequently during naming learned the word–object relations. The findings suggest that maternal naming and infants' word‐mapping abilities are bidirectionally related. Variability in infants' attention to maternal multimodal naming explains the variability in early lexical‐mapping development.