Stability and change in young children's linguistic experience during the COVID-19 pandemic: insight from a citizen-science sample in the United States.

Early in the COVID-19 pandemic, extensive lockdowns interrupted daily routines, including childcare. We asked whether these interruptions, and the inevitable changes in the people with whom children spent their waking hours, caused changes in the languages that children heard. We retrospectively queried parents of young children (0-4 years) in the US about childcare arrangements and exposure to English and non-English languages at four timepoints from February 2020 to September 2021. Despite discontinuity in childcare arrangements, we found that children's exposure to English versus other languages remained relatively stable. We also identified demographic variables (child age at pandemic onset, parental proficiency in a non-English language) that consistently predicted exposure to non-English languages. Thus, multilingually-exposed children in this population did not appear to significantly gain or lose the opportunity to hear non-English languages overall. These results provide insight into the experiences of this unique cohort and inform our understanding of how language development can be shaped by complex environmental systems.

The Influence of Memory on Visual Perception in Infants, Children, and Adults.

Perception is not an independent, in-the-moment event. Instead, perceiving involves integrating prior expectations with current observations. How does this ability develop from infancy through adulthood? We examined how prior visual experience shapes visual perception in infants, children, and adults. Using an identical task across age groups, we exposed participants to pairs of colorful stimuli and implicitly measured their ability to discriminate relative saturation levels. Results showed that adult participants were biased by previously experienced exemplars, and exhibited weakened in-the-moment discrimination between different levels of saturation. In contrast, infants and children showed less influence of memory in their perception, and they actually outperformed adults in discriminating between current levels of saturation. Our findings suggest that as humans develop, their perception relies more on prior experience and less on current observation.

Moving beyond "nouns in the lab": Using naturalistic data to understand why infants' first words include uh-oh and hi.

Why do infants learn some words earlier than others? Many theories of early word learning focus on explaining how infants map labels onto concrete objects. However, words that are more abstract than object nouns, such as uh-oh, hi, more, up, and all-gone, are typically among the first to appear in infants' vocabularies. We combined a behavioral experiment with naturalistic observational research to explore how infants learn and represent this understudied category of high-frequency, routine-based non-nouns, which we term "everyday words." In Study 1, we found that a conventional eye-tracking measure of comprehension was insufficient to capture U.S.-based English-learning 10- to 16-month-old infants' emerging understanding of everyday words. In Study 2, we analyzed the visual and social scenes surrounding caregivers' and infants' use of everyday words in a naturalistic video corpus. This ecologically motivated research revealed that everyday words rarely co-occurred with consistent visual referents, making their early learnability difficult to reconcile with dominant word learning theories. Our findings instead point to complex patterns in the types of situations associated with everyday words that could contribute to their early representation in infants' vocabularies. By leveraging both experimental and observational methods, this investigation underscores the value of using naturalistic data to broaden theories of early learning. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Frequent vs. infrequent words shape toddlers' real-time sentence comprehension.

We examined how noun frequency and the typicality of surrounding linguistic context contribute to children's real-time comprehension. Monolingual English-learning toddlers viewed pairs of pictures while hearing sentences with typical or atypical sentence frames (Look at the… vs. Examine the…), followed by nouns that were higher- or lower-frequency labels for a referent (horse vs. pony). Toddlers showed no significant differences in comprehension of nouns in typical and atypical sentence frames. However, they were less accurate in recognizing lower-frequency nouns, particularly among toddlers with smaller vocabularies. We conclude that toddlers can recognize nouns in diverse sentence contexts, but their representations develop gradually.

iCatcher: A neural network approach for automated coding of young children's eye movements.

Infants' looking behaviors are often used for measuring attention, real-time processing, and learning-often using low-resolution videos. Despite the ubiquity of gaze-related methods in developmental science, current analysis techniques usually involve laborious post hoc coding, imprecise real-time coding, or expensive eye trackers that may increase data loss and require a calibration phase. As an alternative, we propose using computer vision methods to perform automatic gaze estimation from low-resolution videos. At the core of our approach is a neural network that classifies gaze directions in real time. We compared our method, called iCatcher, to manually annotated videos from a prior study in which infants looked at one of two pictures on a screen. We demonstrated that the accuracy of iCatcher approximates that of human annotators and that it replicates the prior study's results. Our method is publicly available as an open-source repository at https://github.com/yoterel/iCatcher.

Children simultaneously learn multiple dimensions of information during shared book reading.

Picture books inherently contain many parallel dimensions of information and serve as a rich source of input for children. However, studies of children's learning from picture books tend to focus on a single type of information (e.g., novel words). To better understand the learning-related potential of shared book reading, we examined 4.5- to 5.5-year-old children's simultaneous learning of novel words, moral lessons, and story details from a reading interaction with a parent. Results showed that children successfully learned new words, extracted a moral lesson, and recalled story details from the picture book. Contrary to expectations, children's learning was equally strong regardless of whether or not parents were prompted to focus on learning as the key purpose of book reading. This research demonstrates that children learn diverse information presented across different time scales from picture books.

A multi-lab study of bilingual infants: Exploring the preference for infant-directed speech.

From the earliest months of life, infants prefer listening to and learn better from infant-directed speech (IDS) than adult-directed speech (ADS). Yet, IDS differs within communities, across languages, and across cultures, both in form and in prevalence. This large-scale, multi-site study used the diversity of bilingual infant experiences to explore the impact of different types of linguistic experience on infants' IDS preference. As part of the multi-lab ManyBabies 1 project, we compared lab-matched samples of 333 bilingual and 385 monolingual infants' preference for North-American English IDS (cf. ManyBabies Consortium, 2020: ManyBabies 1), tested in 17 labs in 7 countries. Those infants were tested in two age groups: 6-9 months (the younger sample) and 12-15 months (the older sample). We found that bilingual and monolingual infants both preferred IDS to ADS, and did not differ in terms of the overall magnitude of this preference. However, amongst bilingual infants who were acquiring North-American English (NAE) as a native language, greater exposure to NAE was associated with a stronger IDS preference, extending the previous finding from ManyBabies 1 that monolinguals learning NAE as a native language showed a stronger preference than infants unexposed to NAE. Together, our findings indicate that IDS preference likely makes a similar contribution to monolingual and bilingual development, and that infants are exquisitely sensitive to the nature and frequency of different types of language input in their early environments.

The development of gaze following in monolingual and bilingual infants: A multi-laboratory study.

Determining the meanings of words requires language learners to attend to what other people say. However, it behooves a young language learner to simultaneously encode relevant non-verbal cues, for example, by following the direction of their eye gaze. Sensitivity to cues such as eye gaze might be particularly important for bilingual infants, as they encounter less consistency between words and objects than monolingual infants, and do not always have access to the same word-learning heuristics (e.g., mutual exclusivity). In a preregistered study, we tested the hypothesis that bilingual experience would lead to a more pronounced ability to follow another's gaze. We used a gaze-following paradigm developed by Senju and Csibra (Current Biology, 18, 2008, 668) to test a total of 93 6- to 9-month-old and 229 12- to 15-month-old monolingual and bilingual infants, in 11 laboratories located in 8 countries. Monolingual and bilingual infants showed similar gaze-following abilities, and both groups showed age-related improvements in speed, accuracy, frequency, and duration of fixations to congruent objects. Unexpectedly, bilinguals tended to make more frequent fixations to on-screen objects, whether or not they were cued by the actor. These results suggest that gaze sensitivity is a fundamental aspect of development that is robust to variation in language exposure.

Tuning in to non-adjacencies: Exposure to learnable patterns supports discovering otherwise difficult structures.

Non-adjacent dependencies are ubiquitous in language, but difficult to learn in artificial language experiments in the lab. Previous research suggests that non-adjacent dependencies are more learnable given structural support in the input - for instance, in the presence of high variability between dependent items. However, not all non-adjacent dependencies occur in supportive contexts. How are such regularities learned? One possibility is that learning one set of non-adjacent dependencies can highlight similar structures in subsequent input, facilitating the acquisition of new non-adjacent dependencies that are otherwise difficult to learn. In three experiments, we show that prior exposure to learnable non-adjacent dependencies - i.e., dependencies presented in a learning context that has been shown to facilitate discovery - improves learning of novel non-adjacent regularities that are typically not detected. These findings demonstrate how the discovery of complex linguistic structures can build on past learning in supportive contexts.

Plasticity in second language learning: The case of Mandarin tones.

Adults typically struggle to perceive non-native sound contrasts, especially those that conflict with their first language. Do the same challenges persist when the sound contrasts overlap but do not conflict? To address this question, we explored the acquisition of lexical tones. While tonal variations are present in many languages, they are only used contrastively in tonal languages. We investigated the perception of Mandarin tones by adults with differing experience with Mandarin, including naïve listeners, classroom learners, and native speakers. Naïve listeners discriminated Mandarin tones at above-chance levels, and performance significantly improved after just one month of classroom exposure. Additional evidence for plasticity came from advanced classroom learners, whose tonemic perception was indistinguishable from that of native speakers. The results suggest that unlike many other non-native contrasts, adults studying a language in the classroom can readily acquire the perceptual skills needed to discriminate Mandarin tones.

Infants' selective use of reliable cues in multidimensional language input.

Learning always happens from input that contains multiple structures and multiple sources of variability. Though infants possess learning mechanisms to locate structure in the world, lab-based experiments have rarely probed how infants contend with input that contains many different structures and cues. Two experiments explored infants' use of two naturally occurring sources of variability-different sounds and different people-to detect regularities in language. Monolingual infants (9-10 months) heard a male and female talker produce two different speech streams, one of which followed a deterministic pattern (e.g., AAB, le-le-di) and one of which did not. For half of the infants, each speaker produced only one of the streams; for the other half of the infants, each speaker produced 50% of each stream. In Experiment 1, each stream consisted of distinct sounds, and infants successfully demonstrated learning regardless of the correspondence between speaker and stream. In Experiment 2, each stream consisted of the same sounds, and infants failed to show learning, even when speakers provided a perfect cue for separating each stream. Thus, monolingual infants can learn in the presence of multiple speech streams, but these experiments suggest that infants may rely more on sound-based rather than speaker-based distinctions when breaking into the structure of incoming information. This selective use of some cues over others highlights infants' ability to adaptively focus on distinctions that are most likely to be useful as they sort through their inherently multidimensional surroundings. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Bilingual toddlers' comprehension of mixed sentences is asymmetrical across their two languages.

In bilingual language environments, infants and toddlers listen to two separate languages during the same key years that monolingual children listen to just one and bilinguals rarely learn each of their two languages at the same rate. Learning to understand language requires them to cope with challenges not found in monolingual input, notably the use of two languages within the same utterance (e.g., Do you like the perro? or ¿Te gusta el doggy?). For bilinguals of all ages, switching between two languages can reduce the efficiency in real-time language processing. But language switching is a dynamic phenomenon in bilingual environments, presenting the young learner with many junctures where comprehension can be derailed or even supported. In this study, we tested 20 Spanish-English bilingual toddlers (18- to 30-months) who varied substantially in language dominance. Toddlers' eye movements were monitored as they looked at familiar objects and listened to single-language and mixed-language sentences in both of their languages. We found asymmetrical switch costs when toddlers were tested in their dominant versus non-dominant language, and critically, they benefited from hearing nouns produced in their dominant language, independent of switching. While bilingualism does present unique challenges, our results suggest a united picture of early monolingual and bilingual learning. Just like monolinguals, experience shapes bilingual toddlers' word knowledge, and with more robust representations, toddlers are better able to recognize words in diverse sentences.

Exposure to multiple accents supports infants' understanding of novel accents.

Accented speech poses a challenge for listeners, particularly those with limited knowledge of their language. In a series of studies, we explored the possibility that experience with variability, specifically the variability provided by multiple accents, would facilitate infants' comprehension of speech produced with an unfamiliar accent. 15- and 18-month-old American-English learning infants were exposed to brief passages of multi-talker speech and subsequently tested on their ability to distinguish between real, familiar words and nonsense words, produced in either their native accent or an unfamiliar (British) accent. Exposure passages were produced in a familiar (American) accent, a single unfamiliar (British) accent or a variety of novel accents (Australian, Southern, Indian). While 15-month-olds successfully recognized real words spoken in a familiar accent, they never demonstrated comprehension of English words produced in the unfamiliar accent. 18-month-olds also failed to recognize English words spoken in the unfamiliar accent after exposure to the familiar or single unfamiliar accent. However, they succeeded after exposure to multiple unfamiliar accents, suggesting that as they get older, infants are better able to exploit the cues provided by variable speech. Increased variability across multiple dimensions can be advantageous for young listeners.

Second Language Experience Facilitates Statistical Learning of Novel Linguistic Materials.

Recent research has begun to explore individual differences in statistical learning, and how those differences may be related to other cognitive abilities, particularly their effects on language learning. In this research, we explored a different type of relationship between language learning and statistical learning: the possibility that learning a new language may also influence statistical learning by changing the regularities to which learners are sensitive. We tested two groups of participants, Mandarin Learners and Naïve Controls, at two time points, 6 months apart. At each time point, participants performed two different statistical learning tasks: an artificial tonal language statistical learning task and a visual statistical learning task. Only the Mandarin-learning group showed significant improvement on the linguistic task, whereas both groups improved equally on the visual task. These results support the view that there are multiple influences on statistical learning. Domain-relevant experiences may affect the regularities that learners can discover when presented with novel stimuli.

The role of experience in children's discrimination of unfamiliar languages.

Five- and six-year-old children (n = 160) participated in three studies designed to explore language discrimination. After an initial exposure period (during which children heard either an unfamiliar language, a familiar language, or music), children performed an ABX discrimination task involving two unfamiliar languages that were either similar (Spanish vs. Italian) or different (Spanish vs. Mandarin). On each trial, participants heard two sentences spoken by two individuals, each spoken in an unfamiliar language. The pair was followed by a third sentence spoken in one of the two languages. Participants were asked to judge whether the third sentence was spoken by the first speaker or the second speaker. Across studies, both the difficulty of the discrimination contrast and the relation between exposure and test materials affected children's performance. In particular, language discrimination performance was facilitated by an initial exposure to a different unfamiliar language, suggesting that experience can help tune children's attention to the relevant features of novel languages.