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AbstractRecent studies with infants and adults demonstrate a facilitative role of labels in object categorization. A common interpretation is that labels highlight commonalities between objects. However, direct evidence for such a mechanism is lacking. Using a novel object category with spatially separate features that are either of low or high variability across the stimulus set, we tracked 12‐month‐olds' attention to object features during learning and at test. Learning occurred in both conditions, but what was learned depended on whether or not labels were heard. A detailed analysis of eye movements revealed that infants in the two conditions employed different object processing strategies. In the silent condition, looking patterns were governed exclusively by the variability of object parts. In the label condition, infants' categorization performance was linked to their relative attention to commonalities. Moreover, the commonality focus persisted after learning even in the absence of labels. These findings constitute the first experimental evidence that labels induce a persistent focus on commonalities.

AbstractTo what extent do toddlers have shared vocabularies? We examined CDI data collected from 14,607 infants and toddlers in five countries and measured the amount of variability between individual lexicons during development for both comprehension and production. Early lexicons are highly overlapping. However, beyond 100 words, toddlers share more words with other toddlers in comprehension than in production, even when matched for lexicon sizes. This finding points to a structural difference in early comprehension and production: Toddlers are generalists in comprehension but develop a unique, expressive voice. Variability in production decreases after two years of age, suggesting convergence to a common expressive core vocabulary. We discuss potential exogenous and endogenous contributions to the inverted U‐shaped development observed in young children's expressive lexical variability.

AbstractFor the last 20 years, developmental psychologists have measured the variability in lexical development of infants and toddlers using the MacArthur‐Bates Communicative Development Inventories (CDIs) – the most widely used parental report forms for assessing language and communication skills in infants and toddlers. We show that CDI reports can serve as a basis for estimating infants' and toddlers'total vocabulary sizes, beyond serving as a tool for assessing their language development relative to other infants and toddlers. We investigate the link between estimated total vocabulary size and raw CDI scores from a mathematical perspective, using both single developmental trajectories and population data. The method capitalizes on robust regularities, such as the overlap of individual vocabularies observed across infants and toddlers, and takes into account both shared knowledge and idiosyncratic knowledge. This statistical approach enables researchers to approximate the total vocabulary size of an infant or a toddler, based on her raw MacArthur‐Bates CDI score. Using the model, we propose new normative data for productive and receptive vocabulary in early childhood, as well as a tabulation that relates individual CDI measures to realistic lexical estimates. The correction required to estimate total vocabulary is non‐linear, with a far greater impact at older ages and higher CDI scores. Therefore, we suggest that correlations of developmental indices to language skills should be made to vocabulary size as estimated by the model rather than to raw CDI scores.

AbstractRecent research has shown that infants are sensitive to mispronunciations of words when tested using a preferential looking task. The results of these studies indicate that infants are able to access the phonological detail of words when engaged in lexical recognition. However, most of this work has focused on mispronunciations of consonants in familiar and novel words. Very little is known about the role that vowels play in constraining lexical access during the early stages of lexical development. We describe a word learning study with 14‐ and 18‐month‐old infants that tests their sensitivity to mispronunciations of word‐medial vowels using a preferential looking task. We found that both age groups demonstrated recognition of correctly pronounced tokens of the newly learnt words but not mispronounced tokens. These results indicate that vowels constrain lexical access of novel words by as early as 14 months of age, and add to the growing body of literature indicating that infants exploit detailed phonological information when processing both familiar and newly learnt words.

AbstractRecent work has investigated the origin of infant colour categories, showing pre‐linguistic infants categorise colour even in the absence of colour words. These infant categories are similar but not identical to adult categories, giving rise to an important question about how infant colour perception changes with the learning of colour words. Here we present two novel paradigms in which 12‐ and 19‐month‐old participants learning English as their first language were assessed on their perception of colour, while data on their colour word comprehension were also collected. Results indicate that participants' perception of colours close to the colour category boundaries dramatically change after colour word learning. The results highlight the shift made from infant colour categories to adult‐like linguistically mediated colour categories that accompanies colour word learning.Research Highlights
We aimed to test whether colour perception is linguistically mediated in infants.
We used novel eye‐tracking and pupillometry paradigms to test infant colour perception either side of learning colour words.
Infants' discrimination of colour changes after learning colour words, suggesting a shift due to colour word learning.
A shift from pre‐linguistic colour representation to linguistically mediated colour representation is discussed.

Infants under 7 months of age fail to reach behind an occluding screen to retrieve a desired toy even though they possess sufficient motor skills to do so. However, even by 3.5 months of age they show surprise if the solidity of the hidden toy is violated, suggesting that they know that the hidden toy still exists. We describe a connectionist model that learns to predict the position of objects and to initiate a response towards these objects. The model embodies the dual‐route principle of object information processing characteristic of the cortex. One route develops a spatially invariant surface feature representation of the object whereas the other route develops a feature blind spatial–temporal representation of the object. The model provides an account of the developmental lag between infants' knowledge of hidden objects and their ability to demonstrate that knowledge in an active retrieval task, in terms of the need to integrate information across multiple object representations using (associative) connectionist learning algorithms. Finally, the model predicts the presence of an early dissociation between infants' ability to use surface features (e.g. colour) and spatial–temporal features (e.g. position) when reasoning about hidden objects. Evidence supporting this prediction has now been reported.

AbstractPrevious behavioural research suggests that infants possess phonologically detailed representations of the vowels and consonants in familiar words. These tasks examine infants' sensitivity to mispronunciations of a target label in the presence of a target and distracter image. Sensitivity to the mispronunciation may, therefore, be contaminated by the degree of mismatch between the distracter label and the heard mispronounced label. Event‐related potential (ERP) studies allow investigation of infants' sensitivity to the relationship between a heard label (correct or mispronounced) and the referent alone using single picture trials. ERPs also provide information about the timing of lexico‐phonological activation in infant word recognition. The current study examined 14‐month‐olds' sensitivity to vowel mispronunciations of familiar words using ERP data from single picture trials. Infants were presented with familiar images followed by a correct pronunciation of its label, a vowel mispronunciation or a phonologically unrelated non‐word. The results support and extend previous behavioural findings that 14‐month‐olds are sensitive to mispronunciations of the vowels in familiar words using an ERP task. We suggest that the presence of pictorial context reinforces infants' sensitivity to mispronunciations of words, and that mispronunciation sensitivity may rely on infants accessing the cross‐modal associations between word forms and their meanings.

Seventeen‐month‐old infants were presented with pairs of images, in silence or with the non‐directive auditory stimulus 'look!'. The images had been chosen so that one image depicted an item whose name was known to the infant, and the other image depicted an image whose name was not known to the infant. Infants looked longer at images for which they had names than at images for which they did not have names, despite the absence of any referential input. The experiment controlled for the familiarity of the objects depicted: in each trial, image pairs presented to infants had previously been judged by caregivers to be of roughly equal familiarity.From a theoretical perspective, the results indicate that objects with names are of intrinsic interest to the infant. The possible causal direction for this linkage is discussed and it is concluded that the results are consistent with Whorfian linguistic determinism, although other construals are possible. From a methodological perspective, the results have implications for the use of preferential looking as an index of early word comprehension.

AbstractA substantial body of evidence demonstrates that infants understand the meaning of spoken words from as early as 6 months. Yet little is known about their ability to do so in the absence of any visual referent, which would offer diagnostic evidence for an adult‐like, symbolic interpretation of words and their use in language mediated thought. We used the head‐turn preference procedure to examine whether infants can generate implicit meanings from word forms alone as early as 18 months of age, and whether they are sensitive to meaningful relationships between words. In one condition, toddlers were presented with lists of words taken from the same taxonomic category (e.g. animals or body parts). In a second condition, words taken from two other categories (e.g. clothes and food items) were interleaved within the same list. Listening times were found to be longer in the related‐category condition than in the mixed‐category condition, suggesting that infants extract the meaning of spoken words and are sensitive to the semantic relatedness between these words. Our results show that infants have begun to construct the rudiments of a semantic system based on taxonomic relations even before they enter a period of accelerated vocabulary growth.

AbstractThe current study examines the relationship between 18‐month‐old toddlers' vocabulary size and their ability to inhibit attention to no‐longer relevant information using the backward semantic inhibition paradigm. When adults switch attention from one semantic category to another, the former and no‐longer‐relevant semantic category becomes inhibited, and subsequent attention to an item that belongs to the inhibited semantic category is impaired. Here we demonstrate that 18‐month‐olds can inhibit attention to no‐longer relevant semantic categories, but only if they have a relatively large vocabulary. These findings suggest that an increased number of items (word knowledge) in the toddler lexical‐semantic system during the "vocabulary spurt" at 18‐months may be an important driving force behind the emergence of a semantic inhibitory mechanism. Possessing more words in the mental lexicon likely results in the formation of inhibitory links between words, which allow toddlers to select and deselect words and concepts more efficiently. Our findings highlight the role of vocabulary growth in the development of inhibitory processes in the emerging lexical‐semantic system.

AbstractA broad range of studies demonstrate that sleep has a facilitating role in memory consolidation (see Rasch & Born, ). Whether sleep‐dependent memory consolidation is also apparent in infants in their first few months of life has not been investigated. We demonstrate that 3‐month‐old infants only remember a cartoon face approximately 1.5–2 hours after its first presentation when a period of sleep followed learning. Furthermore, habituation time, that is, the time to become bored with a stimulus shown repetitively, correlated negatively with the density of infant sleep spindles, implying that processing speed is linked to specific electroencephalographic components of sleep. Our findings show that without a short period of sleep infants have problems remembering a newly seen face, that sleep enhances memory consolidation from a very early age, highlighting the importance of napping in infancy, and that infant sleep spindles may be associated with some aspects of cognitive ability.