Previous studies have found correlations between parent input and child language outcomes, providing prima facie evidence for a causal relation. However, this could also reflect the effects of shared genes. The present study removed this genetic confound by measuring English vocabulary growth in 29 preschool-aged children (21 girls) aged 31- to 73-months and 17 infants (all girls) aged 15- to 32-months adopted from China and Eastern Europe and comparing it to speech produced by their adoptive mothers. Vocabulary growth in both groups was correlated with maternal input features; in infants with mean-length of maternal utterance, and in preschoolers with both mean-length of utterance and lexical diversity. Thus, input effects on language outcomes persist even in the absence of genetic confounds.

Both 5-year-old children and adults infer the structure of a sentence as they are hearing it. Prior work, however, has found that children do not always make use of the same information that adults do to guide these inferences. Specifically, when hearing ambiguous sentences like "You can tickle the frog with the feather," children seem to ignore the aspects of the referential context that adults rely on to resolve the ambiguity-e.g., are there two frogs in the scene, one with a feather and one without? Or is there only one frog to be tickled by using a feather? The present study explored two hypotheses about children's failure to use high-level, top-down context cues to infer the structure of these ambiguous sentences: First, children may be less likely to use any top-down cue during comprehension. Second, children may only have difficulties with top-down cues that are unreliable predictors of which syntactic structure is being used. Thus, to disentangle these hypotheses, we conducted a visual world study of adults' and children's ambiguity resolution, manipulating a more reliable top-down cue (the plausibility of the interpretation) and pitting it against a robust bottom-up cue (lexical biases). We find that adults' and children's final interpretations are influenced by both sources of information: adults, however, give greater weight to the top-down cue, whereas children primarily rely on the bottom-up cue. Thus, children's tendency to make minimal use of top-down information persists even when this information is highly valid and dominates adult comprehension. We propose that children have a systematic propensity to rely on bottom-up processing to a greater degree than adults, which could reflect differences in the architecture of the adult and child language comprehension systems or differences in processing speed.

Early cognitive development relies on the sensory experiences that infants acquire as they explore their environment. Atypical experience in one sensory modality from birth may result in fundamental differences in general cognitive abilities. The primary aim of the current study was to compare visual habituation in infants with profound hearing loss, prior to receiving cochlear implants (CIs), and age-matched peers with typical hearing. Two complementary measures of cognitive function and attention maintenance were assessed: the length of time to habituate to a visual stimulus, and look-away rate during habituation. Findings revealed that deaf infants were slower to habituate to a visual stimulus and demonstrated a lower look-away rate than hearing infants. For deaf infants, habituation measures correlated with language outcomes on standardized assessments before cochlear implantation. These findings are consistent with prior evidence suggesting that habituation and look-away rates reflect efficiency of information processing and may suggest that deaf infants take longer to process visual stimuli relative to the hearing infants. Taken together, these findings are consistent with the hypothesis that hearing loss early in infancy influences aspects of general cognitive functioning.

Early auditory/language experience plays an important role in language development. In this study, we examined the effects of severe-to-profound hearing loss and subsequent cochlear implantation on the development of attention to speech in children with cochlear implants (CIs). In addition, we investigated the extent to which attention to speech may predict spoken language development in children with CIs. We tested children with CIs and compared them to chronologically age-matched peers with normal hearing (NH) on their attention to speech at four time points post implantation; specifically, less than 1 month, 3 to 6 months, 12 months, and 18 months post implantation. We also collected a variety of well-established speech perception and spoken language measures from the children with CIs in a 10-year longitudinal study. Children with CIs showed reduced attention to speech as compared to their peers with NH at less than 1 month post implantation, but a similar degree of attention to speech as their NH peers during later time points. In addition, attention to speech at 3 to 6 months post implantation predicts speech perception in children with CIs. These results inform language acquisition theories and bring insights into our understanding of early severe-to-profound hearing loss on infants' attention to speech skills. In addition, the findings have significant clinical implications for early intervention on hearing loss, which emphasizes the importance of developing strong listening skills. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=f7xiYo3Ua08&feature=youtu.be.

Although much is known about the pathology of Bacillus thuringiensis against invertebrates, current understanding of its natural ecology is limited. This study evaluated the biodiversity of B.thuringiensis in relation to its interaction with plants. Phylogenetic relationships between 44 reference and field-collected strains, determined using 16S rRNA and gyrB gene sequences, revealed a high degree of variability, similar to that found in databases. An Arabidopsis thaliana in vitro inoculation model was developed to screen the ability of B.thuringiensis to colonise roots. Significant colonisation differences up to 91-fold were observed between strains, and correlation between strain phylogeny and colonisation was found. The genetics and biochemistry of auxin production; presence of the gene encoding indole pyruvate decarboxylase; and the abilities of Bt strains to swarm, grow in rich/minimal media and affect root growth differed between the strains, but only auxin production correlated significantly with ability to colonise roots. Co-inoculation with Burkholderia phytofirmans PsJN or Pseudomonas fluorescens SBW25 produced no effect on B.thuringiensis colonisation levels, regardless of the co-inoculant. Similarly, root colonisation of A.thaliana mutants impaired in plant defences was not significantly higher compared with controls. This is the first systematic and phylogenetic evaluation of B.thuringiensis interaction with plants.

Languages differ in how they package the components of an event into words to form sentences. For example, while some languages typically encode the manner of motion in the verb (e.g., running), others more often use verbs that encode the path (e.g., ascending). Prior research has demonstrated that children and adults have lexicalization biases; that is, they assume that novel motion verbs will reflect the dominant pattern of their own language. These experiments explored the plasticity of these biases. In Experiments 1 and 2 we taught English-speaking adults motion verbs, varying the proportion of manner and path verbs in the training set; their interpretation of subsequent verbs closely reflected the probabilistic variation in the input. In Experiments 3 and 4, 5-year-old children also systematically shifted their lexicalization biases to reflect the verbs that they were taught. We conclude that lexicalization biases are adaptive inferences about verb meaning that are updated on the basis of experience.

The first aim of this dissertation was to determine whether early deafness is related to children's nonverbal cognitive abilities. Performance of a group of deaf infants were compared to that of same-aged hearing infants on visual sequence learning (VSL) and visual recognition memory (VRM) tasks. The hypothesis was that if deafness is negatively related to general cognitive ability, then the deaf infants would perform more poorly than same-aged hearing infants on the two tasks. There were no significant differences in VSL (n = 19) or VRM (n = 13) performance between the two groups (Chapter III). These results are inconclusive due to the small sample sizes, but importantly, there were individual infants in both groups who demonstrated learning on the two nonverbal tasks. The second aim was to determine whether VSL and VRM ability can provide predictive information about spoken language development. The results for the normal hearing 8.5-month-olds provide evidence for a significant relation between VSL ability and spoken language outcomes (Chapter IV). Specifically, it was found that sequence learning (thought to rely on procedural memory ability) may contribute to vocabulary and gestural development in normal-hearing infants. Further research with larger samples of infants is needed to determine whether procedural learning may be important for grammar acquisition. These results suggest that VSL ability may not be related to spoken language outcomes for deaf infants who use cochlear implants (Chapter V), although VRM ability may be (Chapter VI). If this pattern of results held up for a larger sample of deaf infants, this would suggest that the nonverbal cognitive abilities tapped in the VSL and VRM tasks are not critical for at least some aspects of spoken language development in deaf children who use cochlear implants, and that potential deficits in nonverbal cognitive ability are not necessarily associated with poorer spoken language ability in this population. In future research a larger sample of deaf infants should be recruited in order to clarify whether nonverbal cognitive skills are related to early deafness, and how those nonverbal skills might relate to spoken language development in this unique population.

Early language development is characterized by predictable changes in the words children produce and the complexity of their utterances. In infants, these changes could reflect increasing linguistic expertise or cognitive maturation and development. To disentangle these factors, we compared the acquisition of English in internationally-adopted preschoolers and internationally-adopted infants. Parental reports and speech samples were collected for 1 year. Both groups showed the qualitative shifts that characterize first-language acquisition. Initially, they produced single-word utterances consisting mostly of nouns and social words. The appearance of verbs, adjectives and multiword utterances was predicted by vocabulary size in both groups. Preschoolers did learn some words at an earlier stage than infants, specifically words referring to the past or future and adjectives describing behavior and internal states. These findings suggest that cognitive development plays little role in the shift from referential terms to predicates but may constrain children's ability to learn some abstract words.

Research suggests that non-linguistic sequence learning abilities are an important contributor to language development (Conway, Bauernschmidt, Huang, & Pisoni, 2010). The current study investigated visual sequence learning as a possible predictor of vocabulary development in infants. Fifty-eight 8.5-month-old infants were presented with a three-location spatiotemporal sequence of multi-colored geometric shapes. Early language skills were assessed using the MacArthur-Bates CDI. Analyses of children's reaction times to the stimuli suggest that the extent to which infants demonstrated learning was significantly correlated with their vocabulary comprehension at the time of test and with their gestural comprehension abilities 5 months later. These findings suggest that visual sequence learning may have both domain-general and domain-specific associations with language learning.

There is ample evidence for a connection between linguistic abilities and performance in theory of mind tasks (ToM), however there is considerable dispute about precisely how these domains are linked. Disentangling the causal relations between domains in typically developing children is tricky because many skills are developing in synchrony. If ToM performance depends upon children’s current linguistic abilities, then the relation should be present even when language acquisition is delayed. We explored these issues in a group of late English learners, 45 internationally adopted children who came to the US at 2.5 years or older, and a control group of language matched preschoolers who were learning English as a first language. The children were tested on general English language abilities, sentence complement comprehension, English vocabulary and ToM. The two groups performed similarly on standard verbal ToM tasks, even though the adopted group was on average nearly 3 years older. However, the adopted children outperformed the controls in ToM tasks with reduced linguistic demands. General language skills predicted ToM ability in both groups and complement comprehension did not account for any additional variance. The data suggests that executive functioning along with general language skills may be the critical components in ToM success.

Language development is characterized by predictable shifts in the words children produce and the complexity of their utterances. Because acquisition typically occurs simultaneously with maturation and cognitive development, it is difficult to determine the causes of these shifts. We explored how acquisition proceeds in the absence of possible cognitive or maturational roadblocks, by examining the acquisition of English in internationally adopted preschoolers. Like infants, and unlike other second-language learners, these children acquire language from child-directed speech, without access to bilingual informants. Parental reports and speech samples were collected from 27 preschoolers, 3 to 18 months after they were adopted from China. These children showed the same developmental patterns in language production as monolingual infants (matched for vocabulary size). Early on, their vocabularies were dominated by nouns, their utterances were short, and grammatical morphemes were generally omitted. Children at later stages had more diverse vocabularies and produced longer utterances with more grammatical morphemes.

Language development is characterized by predictable shifts in the words children produce and the complexity of their utterances. Because acquisition typically occurs simultaneously with maturation and cognitive development, it is difficult to determine the causes of these shifts. We explored how acquisition proceeds in the absence of possible cognitive or maturational roadblocks, by examining the acquisition of English in internationally adopted preschoolers. Like infants, and unlike other second-language learners, these children acquire language from child-directed speech, without access to bilingual informants. Parental reports and speech samples were collected from 27 preschoolers, 3 to 18 months after they were adopted from China. These children showed the same developmental patterns in language production as monolingual infants (matched for vocabulary size). Early on, their vocabularies were dominated by nouns, their utterances were short, and grammatical morphemes were generally omitted. Children at later stages had more diverse vocabularies and produced longer utterances with more grammatical morphemes.