Children and adults produce distinct technology- and human-directed speech.

This study compares how English-speaking adults and children from the United States adapt their speech when talking to a real person and a smart speaker (Amazon Alexa) in a psycholinguistic experiment. Overall, participants produced more effortful speech when talking to a device (longer duration and higher pitch). These differences also varied by age: children produced even higher pitch in device-directed speech, suggesting a stronger expectation to be misunderstood by the system. In support of this, we see that after a staged recognition error by the device, children increased pitch even more. Furthermore, both adults and children displayed the same degree of variation in their responses for whether "Alexa seems like a real person or not", further indicating that children's conceptualization of the system's competence shaped their register adjustments, rather than an increased anthropomorphism response. This work speaks to models on the mechanisms underlying speech production, and human-computer interaction frameworks, providing support for routinized theories of spoken interaction with technology.

Statistical word segmentation: Anchoring learning across contexts.

The present experiments were designed to assess infants' abilities to use syllable co-occurrence regularities to segment fluent speech across contexts. Specifically, we investigated whether 9-month-old infants could use statistical regularities in one speech context to support speech segmentation in a second context. Contexts were defined by different word sets representing contextual differences that might occur across conversations or utterances. This mimics the integration of information across multiple interactions within a single language, which is critical for language acquisition. In particular, we performed two experiments to assess whether a statistically segmented word could be used to anchor segmentation in a second, more challenging context, namely speech with variable word lengths. The results of Experiment 1 were consistent with past work suggesting that statistical learning may be hindered by speech with word-length variability, which is inherent to infants' natural speech environments. In Experiment 2, we found that infants could use a previously statistically segmented word to support word segmentation in a novel, challenging context. We also present findings suggesting that this ability was associated with infants' early word knowledge but not their performance on a cognitive development assessment.

Activation for newly learned words in left medial-temporal lobe during toddlers' sleep is associated with memory for words.

Little is known about the neural substrates underlying early memory functioning. To gain more insight, we examined how toddlers remember newly learned words. Hippocampal and anterior medial-temporal lobe (MTL) processes have been hypothesized to support forming and retaining the association between novel words and their referents, but direct evidence of this connection in early childhood is lacking. We assessed 2-year-olds (n = 38) for their memory of newly learned pseudowords associated with novel objects and puppets. We tested memory for these associations during the same session as learning and after a 1-week delay. We then played these pseudowords, previously known words, and completely novel pseudowords during natural nocturnal sleep, while collecting functional magnetic resonance imaging data. Activation in the left hippocampus and the left anterior MTL for newly learned compared to novel words was associated with same-session memory for these newly learned words only when they were learned as puppet names. Activation for known words was associated with memory for puppet names at the 1-week delay. Activation for newly learned words was also associated with overall productive vocabulary. These results underscore an early developing link between memory mechanisms and word learning in the medial temporal lobe.

Selectivity in bilingual nonspeech label learning.

This research investigates selectivity in word learning for bilingual infants. Previous work demonstrated that bilingual infants show greater openness to non-native language sounds in object labels than monolinguals (Hay et al., 2015; Singh, 2018). It remains unclear whether bilingual openness extends to nonspeech sounds. We presented 14- and 19-month-old bilinguals with object labels consisting of nonspeech tones. Monolinguals recently displayed learning of the same labels at 14 months, but not 19 months (Graf Estes et al., 2018). In contrast, bilinguals failed to learn the labels. We propose that hearing phonological variation across two languages helps bilinguals reject nonspeech word forms.

One language or two? Navigating cross-language conflict in statistical word segmentation.

Bilingual infants must navigate the similarities and differences between their languages to achieve native proficiency in childhood. Bilinguals learning to find individual words in fluent speech face the possibility of conflicting cues to word boundaries across their languages. Despite this challenge, bilingual infants typically begin to segment and learn words in both languages around the same time as monolinguals. It is possible that early bilingual experience may support infants' abilities to track regularities relevant for word segmentation separately across their languages. In a dual speech stream statistical word segmentation task, we assessed whether 16-month-old infants could track syllable co-occurrence regularities in two artificial languages despite conflicting information across the languages. We found that bilingual, but not monolingual, infants were able to segment the dual speech streams using statistical regularities. Although the two language groups did not differ on secondary measures of cognitive and linguistic development, bilingual infants' real-world experience with bilingual speakers was predictive of their performance in the dual language statistical segmentation task.

Specificity of representations in infants' visual statistical learning.

Past work has demonstrated infants' robust statistical learning across visual and auditory modalities. However, the specificity of representations produced via visual statistical learning has not been fully explored. The current study addressed this by investigating infants' abilities to identify previously learned object sequences when some object features (e.g., shape, face) aligned with prior learning and other features did not. Experiment 1 replicated past work demonstrating that infants can learn statistical regularities across sequentially presented objects and extended this finding to 16-month-olds. In Experiment 2, infants viewed test sequences in which one object feature (e.g., face) had been removed but the other feature (e.g., shape) was maintained, resulting in failure to identify familiar sequences. We further probed learning specificity by assessing infants' recognition of sequences when one feature was altered rather than removed (Experiment 3) and when one feature was uncorrelated with the original sequence structure (Experiment 4). In both cases, infants failed to identify sequences in which object features were not identical between learning and test. These findings suggest that infants are limited in their ability to generalize the statistical structure of an object sequence when the objects' features do not align between learning and test.

Learning across languages: bilingual experience supports dual language statistical word segmentation.

Bilingual acquisition presents learning challenges beyond those found in monolingual environments, including the need to segment speech in two languages. Infants may use statistical cues, such as syllable-level transitional probabilities, to segment words from fluent speech. In the present study we assessed monolingual and bilingual 14-month-olds' abilities to segment two artificial languages using transitional probability cues. In Experiment 1, monolingual infants successfully segmented the speech streams when the languages were presented individually. However, monolinguals did not segment the same language stimuli when they were presented together in interleaved segments, mimicking the language switches inherent to bilingual speech. To assess the effect of real-world bilingual experience on dual language speech segmentation, Experiment 2 tested infants with regular exposure to two languages using the same interleaved language stimuli as Experiment 1. The bilingual infants in Experiment 2 successfully segmented the languages, indicating that early exposure to two languages supports infants' abilities to segment dual language speech using transitional probability cues. These findings support the notion that early bilingual exposure prepares infants to navigate challenging aspects of dual language environments as they begin to acquire two languages.

Caregivers and strangers: The influence of familiarity on gaze following and learning.

This study examines how social cues facilitate learning by manipulating the familiarity of a social cue. Participants were forty-nine infants between 12-18 months. Infants were taught a novel label for a novel object under two pre-recorded gaze conditions-one in which the caregiver was seen gazing at a novel object while a verbal label was played, and one in which a stranger was seen gazing at a novel object while a verbal label was played. Learning was only evident in the caregiver condition and only in the infants most skilled at following their caregivers' gaze. The results of the current study suggest that both the familiarity of the cuer and the infant's own ability to follow the gaze of the cuer play important roles in the infant's learning in this task.

Infants with Williams syndrome detect statistical regularities in continuous speech.

Williams syndrome (WS) is a rare genetic disorder associated with delays in language and cognitive development. The reasons for the language delay are unknown. Statistical learning is a domain-general mechanism recruited for early language acquisition. In the present study, we investigated whether infants with WS were able to detect the statistical structure in continuous speech. Eighteen 8- to 20-month-olds with WS were familiarized with 2min of a continuous stream of synthesized nonsense words; the statistical structure of the speech was the only cue to word boundaries. They were tested on their ability to discriminate statistically-defined "words" and "part-words" (which crossed word boundaries) in the artificial language. Despite significant cognitive and language delays, infants with WS were able to detect the statistical regularities in the speech stream. These findings suggest that an inability to track the statistical properties of speech is unlikely to be the primary basis for the delays in the onset of language observed in infants with WS. These results provide the first evidence of statistical learning by infants with developmental delays.

Finding patterns and learning words: Infant phonotactic knowledge is associated with vocabulary size.

Native language statistical regularities about allowable phoneme combinations (i.e., phonotactic patterns) may provide learners with cues to support word learning. The current research investigated the association between infants' native language phonotactic knowledge and their word learning progress, as measured by vocabulary size. In the experiment, 19-month-old infants listened to a corpus of nonce words that contained novel phonotactic patterns. All words began with "illegal" consonant clusters that cannot occur in native (English) words. The rationale for the task was that infants with fragile phonotactic knowledge should exhibit stronger learning of the novel illegal phonotactic patterns than infants with robust phonotactic knowledge. We found that infants with smaller vocabularies showed stronger phonotactic learning than infants with larger vocabularies even after accounting for general cognition. We propose that learning about native language structure may promote vocabulary development by providing a foundation for word learning; infants with smaller vocabularies may have weaker support from phonotactics than infants with larger vocabularies. Furthermore, stored vocabulary knowledge may promote the detection of phonotactic patterns even during infancy.

Domain general learning: Infants use social and non-social cues when learning object statistics.

Previous research has shown that infants can learn from social cues. But is a social cue more effective at directing learning than a non-social cue? This study investigated whether 9-month-old infants (N = 55) could learn a visual statistical regularity in the presence of a distracting visual sequence when attention was directed by either a social cue (a person) or a non-social cue (a rectangle). The results show that both social and non-social cues can guide infants' attention to a visual shape sequence (and away from a distracting sequence). The social cue more effectively directed attention than the non-social cue during the familiarization phase, but the social cue did not result in significantly stronger learning than the non-social cue. The findings suggest that domain general attention mechanisms allow for the comparable learning seen in both conditions.

From flexibility to constraint: the contrastive use of lexical tone in early word learning.

Infants must develop both flexibility and constraint in their interpretation of acceptable word forms. The current experiments examined the development of infants' lexical interpretation of non-native variations in pitch contour. Fourteen-, 17-, and 19-month-olds (Experiments 1 and 2, N = 72) heard labels for two novel objects; labels contained the same syllable produced with distinct pitch contours (Mandarin lexical tones). The youngest infants learned the label-object mappings, but the older groups did not, despite being able to discriminate pitch differences in an object-free task (Experiment 3, N = 14). Results indicate that 14-month-olds remain flexible regarding what sounds make meaningful distinctions between words. By 17-19 months, experience with a nontonal native language constrains infants' interpretation of lexical tone.

Learning builds on learning: infants' use of native language sound patterns to learn words.

The current research investigated how infants apply prior knowledge of environmental regularities to support new learning. The experiments tested whether infants could exploit experience with native language (English) phonotactic patterns to facilitate associating sounds with meanings during word learning. Infants (14-month-olds) heard fluent speech that contained cues for detecting target words; the target words were embedded in sequences that occur across word boundaries. A separate group heard the target words embedded without word boundary cues. Infants then participated in an object label learning task. With the opportunity to use native language patterns to segment the target words, infants subsequently learned the labels. Without this experience, infants failed. Novice word learners can take advantage of early learning about sounds to scaffold lexical development.

Learning about sounds contributes to learning about words: effects of prosody and phonotactics on infant word learning.

This research investigates how early learning about native language sound structure affects how infants associate sounds with meanings during word learning. Infants (19-month-olds) were presented with bisyllabic labels with high or low phonotactic probability (i.e., sequences of frequent or infrequent phonemes in English). The labels were produced with the predominant English trochaic (strong/weak) stress pattern or the less common iambic (weak/strong) pattern. Using the habituation-based Switch Task to test label learning, we found that infants readily learned high probability trochaic labels. However, they failed to learn low probability labels, regardless of stress, and failed to learn iambic labels, regardless of phonotactics. Thus, infants required support from both common phoneme sequences and a common stress pattern to map the labels to objects. These findings demonstrate that early word learning is shaped by prior knowledge of native language phonological regularities and provide support for the role of statistical learning in language acquisition.

Infants generalize representations of statistically segmented words.

The acoustic variation in language presents learners with a substantial challenge. To learn by tracking statistical regularities in speech, infants must recognize words across tokens that differ based on characteristics such as the speaker's voice, affect, or the sentence context. Previous statistical learning studies have not investigated how these types of non-phonemic surface form variation affect learning. The present experiments used tasks tailored to two distinct developmental levels to investigate the robustness of statistical learning to variation. Experiment 1 examined statistical word segmentation in 11-month-olds and found that infants can recognize statistically segmented words across a change in the speaker's voice from segmentation to testing. The direction of infants' preferences suggests that recognizing words across a voice change is more difficult than recognizing them in a consistent voice. Experiment 2 tested whether 17-month-olds can generalize the output of statistical learning across variation to support word learning. The infants were successful in their generalization; they associated referents with statistically defined words despite a change in voice from segmentation to label learning. Infants' learning patterns also indicate that they formed representations of across word syllable sequences during segmentation. Thus, low probability sequences can act as object labels in some conditions. The findings of these experiments suggest that the units that emerge during statistical learning are not perceptually constrained, but rather are robust to naturalistic acoustic variation.

Linking sounds to meanings: infant statistical learning in a natural language.

The processes of infant word segmentation and infant word learning have largely been studied separately. However, the ease with which potential word forms are segmented from fluent speech seems likely to influence subsequent mappings between words and their referents. To explore this process, we tested the link between the statistical coherence of sequences presented in fluent speech and infants' subsequent use of those sequences as labels for novel objects. Notably, the materials were drawn from a natural language unfamiliar to the infants (Italian). The results of three experiments suggest that there is a close relationship between the statistics of the speech stream and subsequent mapping of labels to referents. Mapping was facilitated when the labels contained high transitional probabilities in the forward and/or backward direction (Experiment 1). When no transitional probability information was available (Experiment 2), or when the internal transitional probabilities of the labels were low in both directions (Experiment 3), infants failed to link the labels to their referents. Word learning appears to be strongly influenced by infants' prior experience with the distribution of sounds that make up words in natural languages.

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 years 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.

Computational Modeling of Statistical Learning: Effects of Transitional Probability Versus Frequency and Links to Word Learning.

Statistical learning mechanisms play an important role in theories of language acquisition and processing. Recurrent neural network models have provided important insights into how these mechanisms might operate. We examined whether such networks capture two key findings in human statistical learning. In Simulation 1, a simple recurrent network (SRN) performed much like human learners: it was sensitive to both transitional probability and frequency, with frequency dominating early in learning and probability emerging as the dominant cue later in learning. In Simulation 2, an SRN captured links between statistical segmentation and word learning in infants and adults, and suggested that these links arise because phonological representations are more distinctive for syllables with higher transitional probability. Beyond simply simulating general phenomena, these models provide new insights into underlying mechanisms and generate novel behavioral predictions.

Can infants map meaning to newly segmented words? Statistical segmentation and word learning.

The present experiments investigated how the process of statistically segmenting words from fluent speech is linked to the process of mapping meanings to words. Seventeen-month-old infants first participated in a statistical word segmentation task, which was immediately followed by an object-label-learning task. Infants presented with labels that were words in the fluent speech used in the segmentation task were able to learn the object labels. However, infants presented with labels consisting of novel syllable sequences (nonwords; Experiment 1) or familiar sequences with low internal probabilities (part-words; Experiment 2) did not learn the labels. Thus, prior segmentation opportunities, but not mere frequency of exposure, facilitated infants' learning of object labels. This work provides the first demonstration that exposure to word forms in a statistical word segmentation task facilitates subsequent word learning.

Differences in the nonword repetition performance of children with and without specific language impairment: a meta-analysis.

PURPOSE: This study presents a meta-analysis of the difference in nonword repetition performance between children with and without specific language impairment (SLI). The authors investigated variability in the effect sizes (i.e., the magnitude of the difference between children with and without SLI) across studies and its relation to several factors: type of nonword repetition task, age of SLI sample, and nonword length. METHOD: The authors searched computerized databases and reference sections and requested unpublished data to find reports of nonword repetition tasks comparing children with and without SLI. RESULTS: Children with SLI exhibited very large impairments in nonword repetition, performing an average (across 23 studies) of 1.27 standard deviations below children without SLI. A moderator analysis revealed that different versions of the nonword repetition task yielded significantly different effect sizes, indicating that the measures are not interchangeable. The second moderator analysis found no association between effect size and the age of children with SLI. Finally, an exploratory meta-analysis found that children with SLI displayed difficulty repeating even short nonwords, with greater difficulty for long nonwords. CONCLUSIONS: These findings have potential to affect how nonword repetition tasks are used and interpreted, and suggest several directions for future research.