The influence of language input on 3-year-olds' learning about novel social categories.

There is considerable variability in the social categories that children essentialize and the types of expectations children form about these categories, suggesting children's essentialist beliefs are shaped by environmental input. Prior studies have shown that exposure to generic statements about a social category promotes essentialist beliefs in 4.5- to 8-year-old children. However, by this age children form essentialist beliefs quite robustly, and thus it is unclear whether generic statements impact children's expectations about social categories at younger ages when essentialist beliefs first begin to emerge. Moreover, in prior studies the generic statements were delivered by an experimenter and carefully controlled, and thus it is unclear whether these statements would have the same impact if they occurred in a somewhat less constrained setting, such as parents reading a picture book to their child. The current study addressed these open questions by investigating whether generic statements delivered during a picture-book interaction with their parents influenced 3-year-olds' expectations about members of a novel social category. Our results showed that children who heard generic statements during the picture-book interaction used social-group membership to make inferences about the likely behavior of a novel category member, whereas children who were not exposed to generic statements did not. These findings suggest that as early as 3 years of age, children's expectations about social categories are influenced by generic statements that occur during brief parent-child interactions.

Financial concern reduces child directed speech in a socioeconomically diverse sample.

Socioeconomic status predicts the quantity and nature of child-directed speech that parents produce. However, the mechanisms underlying this relationship remain unclear. This study investigated whether the cognitive load imposed by resource scarcity suppresses parent talk by examining time-dependent variation in child-directed speech in a socioeconomically diverse sample. We predicted that child-directed speech would be lowest at the end of the month when Americans report the greatest financial strain. 166 parents and their 2.5 to 3-year-old children (80 female) participated in a picture-book activity; the number of utterances, word tokens, and word types used by parents were calculated. All three parent language measures were negatively correlated with the date of the month the activity took place, and this relationship did not vary with parental education. These findings suggest that above and beyond individual properties of parents, contextual factors such as financial concerns exert influence on how parents interact with their children.

Associations Between Sleep and Mental Health Among Latina Adolescent Mothers: The Role of Social Support.

Adolescent mothers experience poorer sleep than adult mothers, and Latina adolescent mothers are at greater risk of postpartum depression compared with other racial/ethnic groups. However, social support may be protective against the negative effects of poor sleep in this population. The current study examined (1) associations between the quality and quantity of Latina adolescent mothers' sleep and mental health (depressive symptoms and anxiety), and (2) whether social support buffered the effects of poor sleep on mental health. A sample of Latina adolescent mothers (N = 84) from an agricultural region in the United States reported on their sleep duration/quality, social support from family, friends, and significant others, and their depressive and anxiety symptoms. Results showed that adolescent mothers reported poorer sleep than pediatric recommendations, and poorer sleep quality was associated with greater depressive and anxiety symptoms. Interestingly, when adolescent mothers reported better sleep, they had fewer depressive symptoms in the context of high support from friends compared with low support from friends. Sleep is important for mental health in Latina adolescent mothers, and better sleep combined with strong social support has positive associations with mental health in this population. Findings hold implications for improving mental health in adolescent mothers.

2.5-year-olds succeed in identity and location elicited-response false-belief tasks with adequate response practice.

Researchers have argued that traditional elicited-response false-belief tasks involve considerable processing demands and hence underestimate children's false-belief understanding. Consistent with this claim, Setoh et al. (2016) recently found that when processing demands were sufficiently reduced, children could succeed in an elicited-response task as early as 2.5 years of age. Here we examined whether 2.5-year-olds could also succeed in a low-demand elicited-response task involving false beliefs about identity, which have been argued to provide a critical test of whether children truly represent beliefs, while also clarifying how the practice trials in Setoh et al.'s task facilitated children's elicited-response performance. 2.5-year-olds were tested in a version of Setoh et al.'s elicited-response task in which they heard a location or identity false-belief story. We varied whether the practice trials had the same type of wh-question as the test trial. Children who heard the same type of wh-question on all trials succeeded regardless of which story they heard (location or identity) and performance did not differ across belief type. This replicates Setoh et al.'s positive results and demonstrates that when processing demands are sufficiently reduced, children can succeed in elicited-response tasks involving false beliefs about object location or identity. This suggests that children are capable of attributing genuine false beliefs prior to 4 years of age. However, children performed at chance if the practice trials involved a different type of wh-question than the test trials, suggesting that at this age practice with the wh-question used in the test trial is essential to children's success.

The Developmental Origins of Syntactic Bootstrapping.

Children use syntax to learn verbs, in a process known as syntactic bootstrapping. The structure-mapping account proposes that syntactic bootstrapping begins with a universal bias to map each noun phrase in a sentence onto a participant role in a structured conceptual representation of an event. Equipped with this bias, children interpret the number of noun phrases accompanying a new verb as evidence about the semantic predicate-argument structure of the sentence, and therefore about the meaning of the verb. In this paper, we first review evidence for the structure-mapping account, and then discuss challenges to the account arising from the existence of languages that allow verbs' arguments to be omitted, such as Korean. These challenges prompt us to (a) refine our notion of the distributional learning mechanisms that create representations of sentence structure, and (b) propose that an expectation of discourse continuity allows children to gather linguistic evidence for each verb's arguments across sentences in a coherent discourse. Taken together, the proposed learning mechanisms and biases sketch a route whereby simple aspects of sentence structure guide verb learning from the start of multi-word sentence comprehension, and do so even if some of the new verb's arguments are omitted due to discourse redundancy.

The relationship between parental mental-state language and 2.5-year-olds' performance on a nontraditional false-belief task.

A growing body of evidence suggests that children succeed in nontraditional false-belief tasks in the first years of life. However, few studies have examined individual differences in infants' and toddlers' performance on these tasks. Here we investigated whether parental use of mental-state language (i.e. think, understand), which predicts children's performance on elicited-response false-belief tasks at older ages, also predicts toddlers' performance on a nontraditional task. We tested 2.5-year-old children in a verbal nontraditional false-belief task that included two looking time measures, anticipatory looking and preferential looking, and measured parents' use of mental-state language during a picture-book task. Parents' use of mental-state language positively predicted children's performance on the anticipatory-looking measure of the nontraditional task. These results provide the first evidence that social factors relate to children's false-belief understanding prior to age 3 and that this association extends to performance on nontraditional tasks. These findings add to a growing number of studies suggesting that mental-state language supports mental-state understanding across the lifespan.

Early False-Belief Understanding.

Intense controversy surrounds the question of when children first understand that others can hold false beliefs. Results from traditional tasks suggest that false-belief understanding does not emerge until about 4 years of age and constitutes a major developmental milestone in social cognition. By contrast, results from nontraditional tasks, which have steadily accumulated over the past 10 years, suggest that false-belief understanding is already present in infants (under age 2 years) and toddlers (age 2-3 years) and thus forms an integral part of social cognition from early in life. Here we first present an overview of the findings from nontraditional tasks. We then return to traditional tasks and argue that processing difficulties, rather than limitations in false-belief understanding, account for young children's failure at these tasks.

Finding meaning in a noisy world: exploring the effects of referential ambiguity and competition on 2·5-year-olds' cross-situational word learning.

While recent studies suggest children can use cross-situational information to learn words, these studies involved minimal referential ambiguity, and the cross-situational evidence overwhelmingly favored a single referent for each word. Here we asked whether 2·5-year-olds could identify a noun's referent when the scene and cross-situational evidence were more ambiguous. Children saw four trials in which a novel word occurred with four novel objects; only one object consistently co-occurred with the word across trials. The frequency of distracter objects varied across conditions. When all distracter referents occurred only once (no-competition), children successfully identified the noun's referent. When a high-probability competitor referent occurred on three trials, children identified the target referent if the competitor was absent on the third trial (short-competition) but not if it was present until the fourth trial (long-competition). This suggests that although 2·5-year-olds' cross-situational learning scales up to more ambiguous scenes, it is disrupted by high-probability competitor referents.

Surprise! 20-month-old infants understand the emotional consequences of false beliefs.

Recent studies suggest that by the second year of life, infants can attribute false beliefs to agents. However, prior studies have largely focused on infants' ability to predict a mistaken agent's physical actions on objects. The present research investigated whether 20-month-old infants could also reason about belief-based emotional displays. In Experiments 1 and 2, infants viewed an agent who shook two objects: one rattled and the other was silent. Infants expected the agent to express surprise at the silent object if she had a false belief that both objects rattled, but not if she was merely ignorant about the objects' properties. Experiment 3 replicated and extended these findings: if an agent falsely believed that two containers held toy bears (when only one did so), infants expected the agent to express surprise at the empty, but not the full, container. Together, these results provide the first evidence that infants in the second year of life understand the causal relationship between beliefs and emotional displays. These findings thus provide new evidence for false-belief understanding in infancy and suggest that infants, like older children, possess a robust understanding of belief that applies to a broad range of belief-based responses.

Rethinking the Relationship between Social Experience and False-Belief Understanding: A Mentalistic Account.

It was long assumed that the capacity to represent false beliefs did not emerge until at least age four, as evidenced by children's performance on elicited-response tasks. However, recent evidence that infants appear to demonstrate false-belief understanding when tested with alternative, non-elicited-response measures has led some researchers to conclude that the capacity to represent beliefs emerges in the 1st year of life. This mentalistic view has been criticized for failing to offer an explanation for the well-established positive associations between social factors and preschoolers' performance on elicited-response false-belief tasks. In this paper, we address this criticism by offering an account that reconciles these associations with the mentalistic claim that false-belief understanding emerges in infancy. We propose that rather than facilitating the emergence of the capacity to represent beliefs, social factors facilitate the use of this ability via effects on attention, inference, retrieval, and response production. Our account predicts that the relationship between social factors and false-belief understanding should not be specific to preschoolers' performance in elicited-response tasks: this relationship should be apparent across the lifespan in a variety of paradigms. We review an accumulating body of evidence that supports this prediction.

Two-and-a-half-year-olds succeed at a traditional false-belief task with reduced processing demands.

When tested with traditional false-belief tasks, which require answering a standard question about the likely behavior of an agent with a false belief, children perform below chance until age 4 y or later. When tested without such questions, however, children give evidence of false-belief understanding much earlier. Are traditional tasks difficult because they tap a more advanced form of false-belief understanding (fundamental-change view) or because they impose greater processing demands (processing-demands view)? Evidence that young children succeed at traditional false-belief tasks when processing demands are reduced would support the latter view. In prior research, reductions in inhibitory-control demands led to improvements in young children's performance, but often only to chance (instead of below-chance) levels. Here we examined whether further reductions in processing demands might lead to success. We speculated that: (i) young children could respond randomly in a traditional low-inhibition task because their limited information-processing resources are overwhelmed by the total concurrent processing demands in the task; and (ii) these demands include those from the response-generation process activated by the standard question. This analysis suggested that 2.5-y-old toddlers might succeed at a traditional low-inhibition task if response-generation demands were also reduced via practice trials. As predicted, toddlers performed above chance following two response-generation practice trials; toddlers failed when these trials either were rendered less effective or were used in a high-inhibition task. These results support the processing-demands view: Even toddlers succeed at a traditional false-belief task when overall processing demands are reduced.

Psychological Reasoning in Infancy.

Adults routinely make sense of others' actions by inferring the mental states that underlie these actions. Over the past two decades, developmental researchers have made significant advances in understanding the origins of this ability in infancy. This evidence indicates that when infants observe an agent act in a simple scene, they infer the agent's mental states and then use these mental states, together with a principle of rationality (and its corollaries of efficiency and consistency), to predict and interpret the agent's subsequent actions and to guide their own actions toward the agent. In this review, we first describe the initial demonstrations of infants' sensitivity to the efficiency and consistency principles. We then examine how infants identify novel entities as agents. Next, we summarize what is known about infants' ability to reason about agents' motivational, epistemic, and counterfactual states. Finally, we consider alternative interpretations of these findings and discuss the current controversy about the relation between implicit and explicit psychological reasoning.

Processing Demands Impact 3-Year-Olds' Performance in a Spontaneous-Response Task: New Evidence for the Processing-Load Account of Early False-Belief Understanding.

Prior to age four, children succeed in non-elicited-response false-belief tasks but fail elicited-response false-belief tasks. To explain this discrepancy, the processing-load account argues that the capacity to represent beliefs emerges in infancy, as indicated by early success on non-elicited-response tasks, but that children's ability to demonstrate this capacity depends on the processing demands of the task and children's processing skills. When processing demands exceed young children's processing abilities, such as in standard elicited-response tasks, children fail despite their capacity to represent beliefs. Support for this account comes from recent evidence that reducing processing demands improves young children's performance: when demands are sufficiently reduced, 2.5-year-olds succeed in elicited-response tasks. Here we sought complementary evidence for the processing-load account by examining whether increasing processing demands impeded children's performance in a non-elicited-response task. 3-year-olds were tested in a preferential-looking task in which they heard a change-of-location false-belief story accompanied by a picture book; across children, we manipulated the amount of linguistic ambiguity in the story. The final page of the book showed two images: one that was consistent with the main character's false belief and one that was consistent with reality. When the story was relatively unambiguous, children looked reliably longer at the false-belief-consistent image, successfully demonstrating their false-belief understanding. When the story was ambiguous, however, this undermined children's performance: looking times to the belief-consistent image were correlated with verbal ability, and only children with verbal skills in the upper quartile of the sample demonstrated a significant preference for the belief-consistent image. These results support the processing-load account by demonstrating that regardless of whether a task involves an elicited response, children's performance depends on the processing demands of the task and their processing skills. These findings also have implications for alternative, deflationary accounts of early false-belief understanding.

Infants understand deceptive intentions to implant false beliefs about identity: New evidence for early mentalistic reasoning.

Are infants capable of representing false beliefs, as the mentalistic account of early psychological reasoning suggests, or are they incapable of doing so, as the minimalist account suggests? The present research sought to shed light on this debate by testing the minimalist claim that a signature limit of early psychological reasoning is a specific inability to understand false beliefs about identity: because of their limited representational capabilities, infants should be unable to make sense of situations where an agent mistakes one object for another, visually identical object. To evaluate this claim, three experiments examined whether 17-month-olds could reason about the actions of a deceptive agent who sought to implant in another agent a false belief about the identity of an object. In each experiment, a thief attempted to secretly steal a desirable rattling toy during its owner's absence by substituting a less desirable silent toy. Infants realized that this substitution could be effective only if the silent toy was visually identical to the rattling toy (Experiment 1) and the owner did not routinely shake her toy when she returned (Experiment 2). When these conditions were met, infants expected the owner to be deceived and to mistake the silent toy for the rattling toy she had left behind (Experiment 3). Together, these results cast doubt on the minimalist claim that infants cannot represent false beliefs about identity. More generally, these results indicate that infants in the 2nd year of life can reason not only about the actions of agents who hold false beliefs, but also about the actions of agents who seek to implant false beliefs, thus providing new support for the mentalistic claim that an abstract capacity to reason about false beliefs emerges early in human development.

Do infants really expect agents to act efficiently? A critical test of the rationality principle.

Recent experiments have suggested that infants' expectations about the actions of agents are guided by a principle of rationality: In particular, infants expect agents to pursue their goals efficiently, expending as little effort as possible. However, these experiments have all presented infants with infrequent or odd actions, which leaves the results open to alternative interpretations and makes it difficult to determine whether infants possess a general expectation of efficiency. We devised a critical test of the rationality principle that did not involve infrequent or odd actions. In two experiments, 16-month-olds watched events in which an agent faced two identical goal objects; although both objects could be reached by typical, everyday actions, one object was physically (Experiment 1) or mentally (Experiment 2) more accessible than the other. In both experiments, infants expected the agent to select the more-accessible object. These results provide new evidence that infants possess a general and robust expectation of efficiency.

Early false-belief understanding in traditional non-Western societies.

The psychological capacity to recognize that others may hold and act on false beliefs has been proposed to reflect an evolved, species-typical adaptation for social reasoning in humans; however, controversy surrounds the developmental timing and universality of this trait. Cross-cultural studies using elicited-response tasks indicate that the age at which children begin to understand false beliefs ranges from 4 to 7 years across societies, whereas studies using spontaneous-response tasks with Western children indicate that false-belief understanding emerges much earlier, consistent with the hypothesis that false-belief understanding is a psychological adaptation that is universally present in early childhood. To evaluate this hypothesis, we used three spontaneous-response tasks that have revealed early false-belief understanding in the West to test young children in three traditional, non-Western societies: Salar (China), Shuar/Colono (Ecuador) and Yasawan (Fiji). Results were comparable with those from the West, supporting the hypothesis that false-belief understanding reflects an adaptation that is universally present early in development.

Children expect generic knowledge to be widely shared.

The ability to acquire and store generic information (that is, information about entire categories) is at the core of human cognition. Remarkably, even young children place special value on generic information, often inferring that it holds important insights about the world. Here, we tested whether children's assumptions about the nature of generic information guide their expectations about how widely known this information is. Across four experiments, 4- to 7-year-old children (N=192) were presented with novel facts in either generic (e.g., "Hedgehogs eat hexapods") or non-generic (e.g., "This hedgehog eats hexapods") format and were asked whether other people (e.g., their moms, grown-ups in general) knew these facts. Overall, children were more likely to say that others knew the generic than the non-generic facts. In addition to highlighting the centrality of generic knowledge in early cognitive life, children's assumption that generic facts are widely known has implications for their social cognition and academic achievement, as well as for the process of language acquisition.

False-belief understanding in 2.5-year-olds: evidence from two novel verbal spontaneous-response tasks.

Recent research indicates that toddlers and infants succeed at various non-verbal spontaneous-response false-belief tasks; here we asked whether toddlers would also succeed at verbal spontaneous-response false-belief tasks that imposed significant linguistic demands. We tested 2.5-year-olds using two novel tasks: a preferential-looking task in which children listened to a false-belief story while looking at a picture book (with matching and non-matching pictures), and a violation-of-expectation task in which children watched an adult 'Subject' answer (correctly or incorrectly) a standard false-belief question. Positive results were obtained with both tasks, despite their linguistic demands. These results (1) support the distinction between spontaneous- and elicited-response tasks by showing that toddlers succeed at verbal false-belief tasks that do not require them to answer direct questions about agents' false beliefs, (2) reinforce claims of robust continuity in early false-belief understanding as assessed by spontaneous-response tasks, and (3) provide researchers with new experimental tasks for exploring early false-belief understanding in neurotypical and autistic populations.