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While previous studies highlight the role that children’s interest in natural categories predict their learning of new label-object associations in these categories, the long-term implications of such a relationship – the extent to which children’s interest shape lexical development – remain unclear. The current study examines whether children’s interests in different natural object categories predict their subsequent interest and the number of words children know in those categories six months later. Using data from sixty-seven children tested at eighteen and twenty-four months of age, we found that parents’ estimates of interest in natural object categories at 18-months predicted their reports of their child’s interests at 24-months. Parent interest reports at 18-months also predicted the number of words that children are reported to know in that category at 24-months. Taken together, this study documents the longitudinal relationship between children’s interests, parents’ awareness of their children’s interests and later vocabulary development.

Synthesized speech technology holds potential for enabling natural conversations between humans and machines, particularly in social robotics. However, the combination of synthesized speech with social robots still lacks some qualities of natural speech, which is crucial for human robot interactions, especially for children. In this study, we recorded the neural activity of 5-year-old, typically developing children from middle to high socio-economic households using EEG while they listened to stories narrated by either an adult or a social robot, specifically Furhat. We measured cortical speech tracking to compare how well children's brains tracked synthesized speech from a robot compared to natural speech from an adult. Our results suggest that children do indeed show cortical speech tracking in both scenarios. The results also suggest that cortical speech tracking requires larger time delays between the speech and the response to reach its peak in child-robot interaction compared to child-adult interaction. Possible sources of these differences along with their implications are discussed.

While much work has emphasized the role of the environment in language learning, research equally reports consistent effects of the child’s knowledge, in particular, the words known to individual children, in steering further lexical development. Much of this work is based on cross-sectional data, assuming that the words typically known to children at n months predict the words typically known to children at n+x months. Given acknowledged variability in the number of words known to individual children at different ages, a more conclusive analysis of this issue requires examination of individual differences in the words learned by individual children across development, i.e., using longitudinal data. In the current study, using longitudinal vocabulary data from children learning Norwegian, we ask whether the phonological connectivity of a word to words that the child already knows or words in the child’s environment predicts the likelihood of the child learning that word across development. The results suggest that the early vocabulary grows predominantly in a rich-get-richer manner, where word learning is predicted by the connectivity of a word to already known words. However, word learning is, to a lesser extent, also influenced by the connectivity of a word to words in the child’s linguistic environment. Our results highlight the promise of using longitudinal data to better understand the factors that influence vocabulary development.

Previous research has suggested that infants and toddlers prioritize the imitation of goals over movements, but recent evidence revealed a more flexible pattern of imitation that depended on the visual saliency or efficiency of movements and goals. This study investigated how visual saliency of action goals alongside verbal information influences toddlers’ action processing and imitation. Twenty- to 22-month-old toddlers observed a toy animal being moved in a particular style toward one of two goals. Goals were either two-dimensional drawings or three-dimensional objects. Before the demonstration, the experimenter provided verbal information about the movement style for one group of toddlers, and about the goal for the other group. Toddlers’ imitation was influenced by goal saliency, verbal information, and an interplay of these factors. Toddlers preferred to imitate the goal over the movement in the 3D condition, and the movement over the goal in the 2D condition, revealing that goal saliency influenced imitation preferences. The effect of verbal cues depended on the order of saliency conditions. Verbal cues impacted imitation only in toddlers who participated in the 2D trials first, indicating that toddlers might be especially susceptible to verbal cues when initial visual information is less salient.

The acquisition of mental language understanding is crucial for the social-cognitive development, especially for the development of Theory of Mind reasoning. While there is evidence for the production of epistemic terms in the third year of life, the comprehension of different degrees of speaker (un-)certainty has not yet been systematically investigated at this age. In the present study, we developed an eyetracking task and measured preferential looking as an indicator of an implicit understanding of the epistemic verbs ‘know’ and ‘think’ in children aged 27 (N = 199) and 36 months (N = 131). Toddlers were faced with two agents who indicated the location of a hidden object (right vs. left box), with a narrator attributing contrasting degrees of certainty to their statements (‘know’ vs. ‘think’) before asking the toddlers about the object’s location. We measured the extent to which children fixated the box associated with the agent described as knowing where the target was and found both at 27 and 36 months of age systematic differences in their looking behaviour to this box across the trial. Children appeared to display a spontaneous preference for the box associated with the agent who knew the target’s location, relative to the agent who only thought the target was in their box in the pre-questioning phase. Subsequently, their preference switched in the post-questioning phase; however, this effect was smaller. These results indicate that toddlers in their third year of life distinguish different degrees of speaker (un-)certainty, expressed by the verbs ‘know’ and 'think'.

Gaze following – infants’ orienting towards an object attended to by their social partner – has been linked to a range of socio-cognitive skills. Despite considerable research on when infants follow the gaze of their social partners, studies have typically examined infants’ following of adults’ gaze. Therefore, little is known about whether or how gaze following is modulated by the characteristics of the model, such as their age. The current study examined infants’ following of the gaze of an actor that varied in age: an adult, a young child, and an infant. In an eyetracking study, 49 infants, aged 6–14 months, were presented with videos in which the actor (either an adult, a child or an infant) first looked down towards a neutral point on the table, then to the participant with a friendly facial expression, and then to one of two novel objects to the left and right of the table. The age of the actor did not predict participants’ gaze following behaviour, with participants following the gaze of the adult, child and same-aged peer. Thus, gaze following is not constrained to interactions with an adult. Furthermore, participants showed high interest in the actors’ faces which was the strongest for the infant actor followed by the child actor, and the adult actor. These results shed insight into the interaction between infants’ gaze following behaviour and their attentional preferences for different social partners. We discuss the implications of these findings for theories of development: Beyond adults, other infants and children are also perceived as interesting social partners and, potentially, valuable sources of information.

Are children and adults sensitive to gaps in their knowledge, and do they actively elicit information to resolve such knowledge gaps? In a cross-situational word learning task, we asked 5-year-olds, 6- to 9-year-olds and adults to estimate their knowledge of newly learned word–object associations. We then examined whether participants preferentially sampled objects they reported not knowing the label in order to hear their labels again. We also examined whether such uncertainty-driven sampling behaviour led to improved learning. We found that all age groups were sensitive to gaps in their knowledge of the word–object associations, i.e. were more likely to say they had correctly indicated the label of an object when they were correct, relative to when they were incorrect. Furthermore, 6- to 9-year-olds and adults—but not 5-year-olds—were more likely to sample objects whose labels they reported not knowing. In other words, older children and adults displayed sampling behaviour directed at reducing knowledge gaps and uncertainty, while younger children did not. However, participants who displayed more uncertainty-driven sampling behaviour were not more accurate at test. Our findings underscore the role of uncertainty in driving 6- to 9-year-olds’ and adults’ sampling behaviour and speak to the mechanisms underlying previously reported performance boosts in active learning.

The current study examines the extent to which children’s interests and caregivers’ sensitivity to their children’s interests are associated with the quality of caregiver-child interaction, and subsequent learning. 81 caregiver-child dyads (24-30-month-old children) completed an online shared book-reading task where caregivers and children read two e-books with pictures and descriptions of objects from different categories – one previously determined to be of low and one of high interest to the child (with one novel word-object mapping introduced in each book). We also obtained separate behavioural indices of children’s interests and children’s later recognition of newly-introduced word-object mappings. Our findings highlight that the quality of caregiver-child interaction is predicted by children’s interests and caregivers’ perception of children’s interests, although we find only limited overlap between our behavioural indices of children’s interests and caregiver perception of children’s interests. Neither of these factors predicted later novel word recognition. Thus, while the dynamics between higher quality of caregiver-child interaction, children’s interests and learning remain inconclusive, caregivers and children appear to be more attentive, enthusiastic and engaged reading about topics that (caregivers believe) interest the child. Furthermore, learning in itself seems to be successful, regardless of factors involved, through the mere task of shared book-reading.

Developmental research utilizes various different methodologies and measures to study the cognitive development of young children; however, the reliability and validity of such measures have been a critical issue in all areas of research practices. To address this problem, particularly in the area of research on infants’ interests, we examined the convergent validity of previously reported measures of children’s interests in natural object categories, as indexed by (1) parents’ estimation of their child’s interest in the categories, (2) extrinsic (overt choices in a task), (3) intrinsic (looking time toward objects), and (4) physiological (pupil dilation) responses to objects of different categories. Additionally, we also examined the discriminant validity of all the aforementioned measures against the well-established and validated measure of parents’ estimations of children’s vocabulary knowledge. Children completed two tasks: (a) an eye-tracking task, where they were presented with images from a range of defined categories, which collected indices of looking time and pupillary activity; (b) a sticker-choice task, where they were asked to choose between two sticker-images from two different categories belonging to the range of categories assessed in the previous task. Parents completed two questionnaires to estimate (i) their child’s interests and (ii) vocabulary knowledge in the categories presented. We first analyzed the discriminant validity between the two parent measures, and found a significant positive association between them. Our successive analyses showed no strong or significant associations between any of our measures, apart from a significant positive association between children’s looking time and parents’ estimations of children’s vocabulary knowledge. From our findings, we conclude that measures of infants’ interests thus far may not have sufficient reliability to adequately capture any potential relationship between these measures, or index different components of interest in young children. We suggest next steps for further validation studies in infant research.

Both words and gestures have been shown to influence object categorization, often even overriding perceptual similarities to cue category membership. However, gestures are often meaningful to infants while words are arbitrarily related to an object they refer to, more similar to arbitrary actions that can be performed on objects. In this study, we examine how words and arbitrary actions shape category formation. Across 3 conditions (word cue, action cue, word-action cue), we presented infants (N = 90) with 8 videos of single-category objects which vary in color and other perceptual features. The objects were either accompanied by a word and/or an action that is being performed on the object. Infants in the word and action condition showed a decrease in looking over the course of the familiarization phase indicating habituation to the category, but infants in the word-action-condition did not. At test, infants saw a novel object of the just-learned category and a novel object from another category side-by-side on the screen. There was some evidence for an advantage for words in shaping early object categorization, although we note that this was not robust across analyses.

Language is learned through social interactions, in which gaze has a special role because it can be used to guide the attention and reference objects easily. Children, starting from very early ages, are also very good at utilizing gaze to map labels to referenced objects. To achieve language teaching robots, we need to understand how these functions of gaze can be implemented most efficiently. To this aim, we allowed children to interact with a social robot to learn the labels of several objects in a naturalistic setting. In some trials the child guided the gaze and chose the object to be learned while the robot was following and in the others they changed the roles and robot guided the gaze and decided on the object to be learned. We measured how much children actually followed the robot’s gaze and how many words they learned in these two conditions, referred to as active and passive learning conditions, respectively. The results indicate that although children followed the robot’s gaze and learned words successfully, there were no meaningful differences inword learning between the two conditions. The rate of gaze following and time spent looking at the robot did not influence word learning, either. The implications of these results for use of robots in educational settings are further discussed.