Nonverbal Action Interpretation Guides Novel Word Disambiguation in 12-Month-Olds.

Whether young infants can exploit sociopragmatic information to interpret new words is a matter of debate. Based on findings and theories from the action interpretation literature, we hypothesized that 12-month-olds should distinguish communicative object-directed actions expressing reference from instrumental object-directed actions indicative of one's goals, and selectively use the former to identify referents of novel linguistic expressions. This hypothesis was tested across four eye-tracking experiments. Infants watched pairs of unfamiliar objects, one of which was first targeted by either a communicative action (e.g., pointing) or an instrumental action (e.g., grasping) and then labeled with a novel word. As predicted, infants fast-mapped the novel words onto the targeted objects after pointing (Experiments 1 and 4) but not after grasping (Experiment 2) unless the grasping action was preceded by an ostensive signal (Experiment 3). Moreover, whenever infants mapped a novel word onto the object indicated by a communicative action, they tended to map a different novel word onto the distractor object, displaying a mutual exclusivity effect. This reliance on nonverbal action interpretation in the disambiguation of novel words indicates that sociopragmatic inferences about reference likely supplement associative and statistical learning mechanisms from the outset of word learning.

Twelve-month-olds disambiguate new words using mutual-exclusivity inferences.

Representing objects in terms of their kinds enables inferences based on the long-term knowledge made available through kind concepts. For example, children readily use lexical knowledge linked to familiar kind concepts to disambiguate new words (e.g., "find the toma"): they exclude members of familiar kinds falling under familiar kind labels (e.g., a ball) as potential referents and link new labels to available unfamiliar objects (e.g., a funnel), a phenomenon dubbed as 'mutual exclusivity'. Younger infants' failure in mutual exclusivity tasks has been commonly interpreted as a limitation of early word-learning or inferential abilities. Here, we investigated an alternative explanation, according to which infants do not spontaneously represent familiar objects under kind concepts, hence lacking access to the information necessary for rejecting them as referents of novel labels. Building on findings about conceptual development and communication, we hypothesized that nonverbal communication could prompt infants to set up kind-based representations which, in turn, would promote mutual exclusivity inferences. This hypothesis was tested in a looking-while-listening task involving novel word disambiguation. Twelve-month-olds saw pairs of objects, one familiar and one unfamiliar, and heard familiar kind labels or novel words. Across two experiments providing a cross-lab replication in two different languages, infants successfully disambiguated novel words when the familiar object had been pointed at before labeling, but not when it had been highlighted in a non-communicative manner (Experiment 1) or not highlighted at all (Experiment 2). Nonverbal communication induced infants to recruit kind-based representations of familiar objects that they failed to recruit in its absence and that, once activated, supported mutual-exclusivity inferences. Developmental changes in children's appreciation of communicative contexts may modulate the expression of early inferential and word learning competences.

Nonverbal category knowledge limits the amount of information encoded in object representations: EEG evidence from 12-month-old infants.

To what extent does language shape how we think about the world? Studies suggest that linguistic symbols expressing conceptual categories ('apple', 'squirrel') make us focus on categorical information (e.g. that you saw a squirrel) and disregard individual information (e.g. whether that squirrel had a long or short tail). Across two experiments with preverbal infants, we demonstrated that it is not language but nonverbal category knowledge that determines what information is packed into object representations. Twelve-month-olds (N = 48) participated in an electroencephalography (EEG) change-detection task involving objects undergoing a brief occlusion. When viewing objects from unfamiliar categories, infants detected both across- and within-category changes, as evidenced by their negative central wave (Nc) event-related potential. Conversely, when viewing objects from familiar categories, they did not respond to within-category changes, which indicates that nonverbal category knowledge interfered with the representation of individual surface features necessary to detect such changes. Furthermore, distinct patterns of γ and α oscillations between familiar and unfamiliar categories were evident before and during occlusion, suggesting that categorization had an influence on the format of recruited object representations. Thus, we show that nonverbal category knowledge has rapid and enduring effects on object representation and discuss their functional significance for generic knowledge acquisition in the absence of language.

Rationality in Joint Action: Maximizing Coefficiency in Coordination.

When people perform simple actions, they often behave efficiently, minimizing the costs of movement for the expected benefit. The present study addressed the question of whether this efficiency scales up to dyads working together to achieve a shared goal: Do people act efficiently as a group (i.e., coefficiently), or do they minimize their own or their partner's individual costs even if this increases the overall cost for the group? We devised a novel, touch-screen-based, sequential object-transfer task to measure how people choose between different paths to coordinate with a partner. Across multiple experiments, we found that participants did not simply minimize their own or their partner's movement costs but made coefficient decisions about paths, which ensured that the aggregate costs of movement for the dyad were minimized. These results suggest that people are able and motivated to make coefficient, collectively rational decisions when acting together.

Lexical Acquisition Through Category Matching: 12-Month-Old Infants Associate Words to Visual Categories.

Although it is widely recognized that human infants build a sizeable conceptual repertoire before mastering language, it remains a matter of debate whether and to what extent early conceptual and category knowledge contributes to language development. We addressed this question by investigating whether 12-month-olds used preverbal categories to discover the meanings of new words. We showed that one group of infants ( n = 18) readily extended novel labels to previously unseen exemplars of preverbal visual categories after only a single labeling episode, but two other groups struggled to do so when taught labels for unfamiliar categories (those who had been previously exposed, n = 18, or not exposed, n = 18, to category tokens). These results suggest that infants expect labels to denote categories of objects and are equipped with learning mechanisms responsible for matching prelinguistic knowledge structures with linguistic inputs. This ability is consistent with the idea that our conceptual machinery provides building blocks for vocabulary and language acquisition.

Motor activation during action perception depends on action interpretation.

Since the discovery of motor mirroring, the involvement of the motor system in action interpretation has been widely discussed. While some theories proposed that motor mirroring underlies human action understanding, others suggested that it is a corollary of action interpretation. We put these two accounts to the test by employing superficially similar actions that invite radically different interpretations of the underlying intentions. Using an action-observation task, we assessed motor activation (as indexed by the suppression of the EEG mu rhythm) in response to actions typically interpreted as instrumental (e.g., grasping) or referential (e.g., pointing) towards an object. Only the observation of instrumental actions resulted in enhanced mu suppression. In addition, the exposure to grasping actions failed to elicit mu suppression when they were preceded by speech, suggesting that the presence of communicative signals modulated the interpretation of the observed actions. These results suggest that the involvement of sensorimotor cortices during action processing is conditional on a particular (instrumental) action interpretation, and that action interpretation relies on inferential processes and top-down mechanisms that are implemented outside of the motor system.

Ratings of age of acquisition of 299 words across 25 languages: Is there a cross-linguistic order of words?

We present a new set of subjective age-of-acquisition (AoA) ratings for 299 words (158 nouns, 141 verbs) in 25 languages from five language families (Afro-Asiatic: Semitic languages; Altaic: one Turkic language: Indo-European: Baltic, Celtic, Germanic, Hellenic, Slavic, and Romance languages; Niger-Congo: one Bantu language; Uralic: Finnic and Ugric languages). Adult native speakers reported the age at which they had learned each word. We present a comparison of the AoA ratings across all languages by contrasting them in pairs. This comparison shows a consistency in the orders of ratings across the 25 languages. The data were then analyzed (1) to ascertain how the demographic characteristics of the participants influenced AoA estimations and (2) to assess differences caused by the exact form of the target question (when did you learn vs. when do children learn this word); (3) to compare the ratings obtained in our study to those of previous studies; and (4) to assess the validity of our study by comparison with quasi-objective AoA norms derived from the MacArthur-Bates Communicative Development Inventories (MB-CDI). All 299 words were judged as being acquired early (mostly before the age of 6 years). AoA ratings were associated with the raters' social or language status, but not with the raters' age or education. Parents reported words as being learned earlier, and bilinguals reported learning them later. Estimations of the age at which children learn the words revealed significantly lower ratings of AoA. Finally, comparisons with previous AoA and MB-CDI norms support the validity of the present estimations. Our AoA ratings are available for research or other purposes.