Infants' understanding of the causal power of agents and tools.

Tools are objects that are manipulated by agents with the intention to cause an effect in the world. We show that the cognitive capacity to understand tools is present in young infants, even if these tools produce arbitrary, causally opaque effects. In experiments 1-2, we used pupillometry to show that 8-mo-old infants infer an invisible causal contact to account for the-otherwise unexplained-motion of a ball. In experiments 3, we probed 8-mo-old infants' account of a state change event (flickering of a cube) that lies outside of the explanatory power of intuitive physics. Infants repeatedly watched an intentional agent launch a ball behind an occluder. After a short delay, a cube, positioned at the other end of the occluder began flickering. Rare unoccluded events served to probe infants' representation of what happened behind the occluder. Infants exhibited larger pupil dilation, signaling more surprise, when the ball stopped before touching the cube, than when it contacted the cube, suggesting that infants inferred that the cause of the state change was contact between the ball and the cube. This effect was canceled in experiment 4, when an inanimate sphere replaced the intentional agent. Altogether, results suggest that, in the infants' eyes, a ball (an inanimate object) has the power to cause an arbitrary state change, but only if it inherits this power from an intentional agent. Eight-month-olds are thus capable of representing complex event structures, involving an intentional agent causing a change with a tool.

Visual object categorization in infancy.

Humans make sense of the world by organizing things into categories. When and how does this process begin? We investigated whether real-world object categories that spontaneously emerge in the first months of life match categorical representations of objects in the human visual cortex. Using eye tracking, we measured the differential looking time of 4-, 10-, and 19-mo-olds as they looked at pairs of pictures belonging to eight animate or inanimate categories (human/nonhuman, faces/bodies, real-world size big/small, natural/artificial). Taking infants' looking times as a measure of similarity, for each age group, we defined a representational space where each object was defined in relation to others of the same or of a different category. This space was compared with hypothesis-based and functional MRI-based models of visual object categorization in the adults' visual cortex. Analyses across different age groups showed that, as infants grow older, their looking behavior matches neural representations in ever-larger portions of the adult visual cortex, suggesting progressive recruitment and integration of more and more feature spaces distributed over the visual cortex. Moreover, the results characterize infants' visual categorization as an incremental process with two milestones. Between 4 and 10 mo, visual exploration guided by saliency gives way to an organization according to the animate-inanimate distinction. Between 10 and 19 mo, a category spurt leads toward a mature organization. We propose that these changes underlie the coupling between seeing and thinking in the developing mind.

Visual Preference for Socially Relevant Spatial Relations in Humans and Monkeys.

As a powerful social signal, a body, face, or gaze facing toward oneself holds an individual's attention. We asked whether, going beyond an egocentric stance, facingness between others has a similar effect and why. In a preferential-looking time paradigm, human adults showed spontaneous preference to look at two bodies facing toward (vs. away from) each other (Experiment 1a, N = 24). Moreover, facing dyads were rated higher on social semantic dimensions, showing that facingness adds social value to stimuli (Experiment 1b, N = 138). The same visual preference was found in juvenile macaque monkeys (Experiment 2, N = 21). Finally, on the human development timescale, this preference emerged by 5 years, although young infants by 7 months of age already discriminate visual scenes on the basis of body positioning (Experiment 3, N = 120). We discuss how the preference for facing dyads-shared by human adults, young children, and macaques-can signal a new milestone in social cognition development, supporting processing and learning from third-party social interactions.

Incomplete language-of-thought in infancy.

The view that infants possess a full-fledged propositional language-of-thought (LoT) is appealing, providing a unifying account for infants' precocious reasoning skills in many domains. However, careful appraisal of empirical evidence suggests that there is still no convincing evidence that infants possess discrete representations of abstract relations, suggesting that infants' LoT remains incomplete. Parallel arguments hold for perception.

Spanish-learning infants switch from a vowel to a consonant bias during the first year of life.

The consonant bias is evidenced by a greater reliance on consonants over vowels in lexical processing. Although attested during adulthood for most Roman and Germanic languages (e.g., French, Italian, English, Dutch), evidence on its development suggests that the native input modulates its trajectory. French and Italian learners exhibit an early switch from a higher reliance on vowels at 5 and 6 months of age to a consonant bias by the end of the first year. This study investigated the developmental trajectory of this bias in a third Romance language unexplored so far-Spanish. In a central visual fixation procedure, infants aged 5, 8½, and 12 months were tested in a word recognition task. In Experiment 1, infants preferred listening to frequent words (e.g., leche, milk) over nonwords (e.g., machi) at all ages. Experiment 2 assessed infants' listening times to consonant and vowel alterations of the words used in Experiment 1. Here, 5-month-olds preferred listening to consonant alterations, whereas 12-month-olds preferred listening to vowel alterations, suggesting that 5-month-olds' recognition performance was more affected by a vowel alteration (e.g., leche →lache), whereas 12-month-olds' recognition performance was more affected by a consonant alteration (e.g., leche →keche). These findings replicate previous findings in Italian and French and generalize them to a third Romance language (Spanish). As such, they support the idea that specific factors common to Romance languages might be driving an early consonant bias in lexical processing.

Visual perception grounding of social cognition in preverbal infants.

Social life is inherently relational, entailing the ability to recognize and monitor social entities and the relationships between them. Very young infants privilege socially relevant entities in the visual world, such as faces and bodies. Here, we show that six-month-old infants also discriminate between configurations of multiple human bodies, based on the internal visuo-spatial relations between bodies, which could cue-or not-social interaction. We measured the differential looking times for two images, each featuring two identical bodies, but in different spatial relations. Infants discriminated between face-to-face and back-to-back body dyads (Experiment 1), and treated face-to-face dyads with higher efficiency (i.e., processing speed), relative to back-to-back dyads (Experiment 2). Looking times for dyads in an asymmetrical relation (i.e., one body facing another without reciprocation) were comparable to looking times for face-to-face dyads, and differed from looking times to back-to-back dyads, suggesting general discrimination between the presence versus absence of relation (Experiment 3). Infants' discrimination of images based on relative positioning of items did not generalize to body-object pairs (Experiment 4). Early sensitivity to the relative positioning of bodies in a scene may be a building block of social cognition, preparing the discovery of the keel and backbone of social life: relations.

Spatial Relations Trigger Visual Binding of People.

To navigate the social world, humans must represent social entities and the relationships between those entities, starting with spatial relationships. Recent research suggests that two bodies are processed with particularly high efficiency in visual perception, when they are in a spatial positioning that cues interaction, that is, close and face-to-face. Socially relevant spatial relations such as facingness may facilitate visual perception by triggering grouping of bodies into a new integrated percept, which would make the stimuli more visible and easier to process. We used EEG and a frequency-tagging paradigm to measure a neural correlate of grouping (or visual binding), while female and male participants saw images of two bodies face-to-face or back-to-back. The two bodies in a dyad flickered at frequency F1 and F2, respectively, and appeared together at a third frequency Fd (dyad frequency). This stimulation should elicit a periodic neural response for each body at F1 and F2, and a third response at Fd, which would be larger for face-to-face (vs. back-to-back) bodies, if those stimuli yield additional integrative processing. Results showed that responses at F1 and F2 were higher for upright than for inverted bodies, demonstrating that our paradigm could capture neural activity associated with viewing bodies. Crucially, the response to dyads at Fd was larger for face-to-face (vs. back-to-back) dyads, suggesting integration mediated by grouping. We propose that spatial relations that recur in social interaction (i.e., facingness) promote binding of multiple bodies into a new representation. This mechanism can explain how the visual system contributes to integrating and transforming the representation of disconnected body shapes into structured representations of social events.

Children's representation of abstract relations in relational/array match-to-sample tasks.

Five experiments compared preschool children's performance to that of adults and of non-human animals on match to sample tasks involving 2-item or 16-item arrays that varied according to their composition of same or different items (Array Match-to-Sample, AMTS). They establish that, like non-human animals in most studies, 3- and 4-year-olds fail 2-item AMTS (the classic relational match to sample task introduced into the literature by Premack, 1983), and that robust success is not observed until age 6. They also establish that 3-year-olds, like non-human animal species, succeed only when they are able to encode stimuli in terms of entropy, a property of an array (namely its internal variability), rather than relations among the individuals in the array (same vs. different), whereas adults solve both 2-item and 16-item AMTS on the basis of the relations same and different. As in the case of non-human animals, the acuity of 3- and 4-year-olds' representation of entropy is insufficient to solve the 2-item same-different AMTS task. At age 4, behavior begins to contrast with that of non-human species. On 16-item AMTS, a subgroup of 4-year-olds induce a categorical rule matching all-same arrays to all-same arrays, while matching other arrays (mixed arrays of same and different items) to all-different arrays. These children tend to justify their choices using the words "same" and "different." By age 4 a number of our participants succeed at 2-item AMTS, also justifying their choices by explicit verbal appeals using words for same and different. Taken together these results suggest that the recruitment of the relational representations corresponding to the meaning of these words contributes to the better performance over the preschool years at solving array match-to-sample tasks.

The Default Computation of Negated Meanings.

Negation is a fundamental component of human reasoning and language. Yet, current neurocognitive models, conceived to account for the cortical representation of meanings (e.g., writing), hardly accommodate the representation of negated meanings (not writing). One main hypothesis, known as the two-step model, proposes that, for negated meanings, the corresponding positive representation is first fully activated and then modified to reflect negation. Recast in neurobiological terms, this model predicts that, in the initial stage of semantic processing, the neural representation of a stimulus' meaning is indistinguishable from the neural representation of that meaning following negation. Although previous work has shown that pragmatic and task manipulations can favor or hinder a two-step processing, we just do not know how the brain processes an utterance as simple as "I am not writing." We implemented two methodologies based on chronometric TMS to measure motor excitability (Experiment 1) and inhibition (Experiment 2) as physiological markers of semantic access to action-related meanings. We used elementary sentences (Adverb + Verb) and a passive reading task. For the first time, we defined action word-related motor activity in terms of increased excitability and concurrently reduced inhibition. Moreover, we showed that this pattern changes already in the earliest stage of semantic processing, when action meanings were negated. Negation modifies the neural representation of the argument in its scope, as soon as semantic effects are observed in the brain.

Infants' representations of same and different in match- and non-match-to-sample.

Three experiments investigated the representations that underlie 14-month-old infants' and adults' success at match-to-sample (MTS) and non-match-to-sample (NMTS) tasks. In Experiment 1, 14-month-old infants were able to learn rules based on abstract representations of sameness and/or difference. When presented with one of eighteen sample stimuli (A) and a choice between a stimulus that was the same as the sample (A) and a different stimulus (B), infants learned to choose A in MTS and B in NMTS. In Experiments 2 and 3, we began to explore the nature of the representations at play in these paradigms. Experiment 2 confirmed that abstract representations were at play, as infants generalized the MTS and NMTS rules to stimuli unseen during familiarization. Experiment 2 also showed that infants tested in MTS learned to seek the stimulus that was the same as the sample, whereas infants tested in NMTS did not learn to seek the different stimulus, but instead learned to avoid the stimulus that was the same as the sample. Infants appeared to only use an abstract representation of the relation same in these experiments. Experiment 3 showed that adult participants, despite knowing the words "same" and "different", also relied on representations of sameness in both MTS and NMTS in a paradigm modeled on that of Experiment 2. We conclude with a discussion of how young infants may possibly represent the abstract relation same.

Newborn's brain activity signals the origin of word memories.

Recent research has shown that specific areas of the human brain are activated by speech from the time of birth. However, it is currently unknown whether newborns' brains also encode and remember the sounds of words when processing speech. The present study investigates the type of information that newborns retain when they hear words and the brain structures that support word-sound recognition. Forty-four healthy newborns were tested with the functional near-infrared spectroscopy method to establish their ability to memorize the sound of a word and distinguish it from a phonetically similar one, 2 min after encoding. Right frontal regions--comparable to those activated in adults during retrieval of verbal material--showed a characteristic neural signature of recognition when newborns listened to a test word that had the same vowel of a previously heard word. In contrast, a characteristic novelty response was found when a test word had different vowels than the familiar word, despite having the same consonants. These results indicate that the information carried by vowels is better recognized by newborns than the information carried by consonants. Moreover, these data suggest that right frontal areas may support the recognition of speech sequences from the very first stages of language acquisition.

The invariance problem in infancy: a pupillometry study.

Despite the fact that no invariant acoustic property corresponds to a single stop consonant coupled with different vowels (e.g., [da], [de], and [du]), adults effortlessly identify the same consonant embedded in different syllables. In so doing, they solve the invariance problem. Can 3- and 6-month-olds solve it as well? To answer this question, we developed a novel methodology based on pupillometry. In Experiment 1, we demonstrated for the first time that infants are sensitive to the distinction between frequent and infrequent acoustic stimuli, showing greater pupil dilation in response to infrequent stimuli. Building on this effect, in Experiment 2, we showed that 6-month-olds, but not 3-month-olds, solve the invariance problem. Moreover, this ability develops before, and therefore independently of, the ability to produce well-formed syllables.

Abstract thematic roles in infants' representation of social events.

Infants' thoughts are classically characterized as iconic, perceptual-like representations.1,2,3 Less clear is whether preverbal infants also possess a propositional language of thought, where mental symbols are combined according to syntactic rules, very much like words in sentences.4,5,6,7,8,9,10,11,12,13,14,15,16,17 Because it is rich, productive, and abstract, a language of thought would provide a key to explaining impressive achievements in early infancy, from logical inference to representation of false beliefs.18,19,20,21,22,23,24,25,26,27,28,29,30,31 A propositional language-including a language of thought5-implies thematic roles that, in a sentence, indicate the relation between noun and verb phrases, defining who acts on whom; i.e., who is the agent and who is the patient.32,33,34,35,36,37,38,39 Agent and patient roles are abstract in that they generally apply to different situations: whether A kicks, helps, or kisses B, A is the agent and B is the patient. Do preverbal infants represent abstract agent and patient roles? We presented 7-month-olds (n = 143) with sequences of scenes where the posture or relative positioning of two individuals indicated that, across different interactions, A acted on B. Results from habituation (experiment 1) and pupillometry paradigms (experiments 2 and 3) demonstrated that infants showed surprise when roles eventually switched (B acted on A). Thus, while encoding social interactions, infants fill in an abstract relational structure that marks the roles of agent and patient and that can be accessed via different event scenes and properties of the event participants (body postures or positioning). This mental process implies a combinatorial capacity that lays the foundations for productivity and compositionality in language and cognition.

Intermodulation responses show integration of interacting bodies in a new whole.

People are often seen among other people, relating to and interacting with one another. Recent studies suggest that socially relevant spatial relations between bodies, such as the face-to-face positioning, or facingness, change the visual representation of those bodies, relative to when the same items appear unrelated (e.g., back-to-back) or in isolation. The current study addresses the hypothesis that face-to-face bodies give rise to a new whole, an integrated representation of individual bodies in a new perceptual unit. Using frequency-tagging EEG, we targeted, as a measure of integration, an EEG correlate of the non-linear combination of the neural responses to each of two individual bodies presented either face-to-face as if interacting, or back-to-back. During EEG recording, participants (N = 32) viewed two bodies, either face-to-face or back-to-back, flickering at two different frequencies (F1 and F2), yielding two distinctive responses in the EEG signal. Spectral analysis examined the responses at the intermodulation frequencies (nF1±mF2), signaling integration of individual responses. An anterior intermodulation response was observed for face-to-face bodies, but not for back-to-back bodies, nor for face-to-face chairs and machines. These results show that interacting bodies are integrated into a representation that is more than the sum of its parts. This effect, specific to body dyads, may mark an early step in the transformation towards an integrated representation of a social event, from the visual representation of individual participants in that event.

The pupil collaboration: A multi-lab, multi-method analysis of goal attribution in infants.

The rise of pupillometry in infant research over the last decade is associated with a variety of methods for data preprocessing and analysis. Although pupil diameter is increasingly recognized as an alternative measure of the popular cumulative looking time approach used in many studies (Jackson & Sirois, 2022), an open question is whether the many approaches used to analyse this variable converge. To this end, we proposed a crowdsourced approach to pupillometry analysis. A dataset from 30 9-month-old infants (15 girls; Mage = 282.9 days, SD = 8.10) was provided to 7 distinct teams for analysis. The data were obtained from infants watching video sequences showing a hand, initially resting between two toys, grabbing one of them (after Woodward, 1998). After habituation, infants were shown (in random order) a sequence of four test events that varied target position and target toy. Results show that looking times reflect primarily the familiar path of the hand, regardless of target toy. Gaze data similarly show this familiarity effect of path. The pupil dilation analyses show that features of pupil baseline measures (duration and temporal location) as well as data retention variation (trial and/or participant) due to different inclusion criteria from the various analysis methods are linked to divergences in findings. Two of the seven teams found no significant findings, whereas the remaining five teams differ in the pattern of findings for main and interaction effects. The discussion proposes guidelines for best practice in the analysis of pupillometry data.

Representations of Abstract Relations in Infancy.

relations are considered the pinnacle of human cognition, allowing for analogical and logical reasoning, and possibly setting humans apart from other animal species. Recent experimental evidence showed that infants are capable of representing the abstract relations same and different, prompting the question of the format of such representations. In a propositional language of thought, abstract relations would be represented in the form of discrete symbols. Is this format available to pre-lexical infants? We report six experiments (N = 192) relying on pupillometry and investigating how preverbal 10- to 12-month-old infants represent the relation same. We found that infants' ability to represent the relation same is impacted by the number of individual entities taking part in the relation. Infants could represent that four syllables were the same and generalized that relation to novel sequences (Experiments 1 and 4). However, they failed to generalize the relation same when it involved 5 or 6 syllables (Experiments 2-3), showing that infants' representation of the relation same is constrained by the limits of working memory capacity. Infants also failed to form a representation equivalent to all the same, which could apply to a varying number of same syllables (Experiments 5-6). These results highlight important discontinuities along cognitive development. Contrary to adults, preverbal infants lack a discrete symbol for the relation same, and rather build a representation of the relation by assembling symbols for individual entities.

Acceleration of information processing en route to perceptual awareness in infancy.

Electrophysiological studies1-6 have suggested an acceleration in information processing in the first years of life, probably largely caused by the progressive myelination of the cortex.7,8 Here, we ask whether and how this acceleration affects information processes that contribute to perceptual awareness. We addressed this issue leveraging on the attentional blink phenomenon9,10 in infants,11 children, and adult participants. When two visual targets (T1 and T2) are to be detected, the observer often misses T2, if it appears shortly after T1, as if the observer's attention blinked. This phenomenon is explained by the two-stage model of perception, where an early unconscious sensory stage is followed by a late and central stage that relies on limited attentional resources.9-14 Although both T1 and T2 are processed in the earlier sensory stage, the capacity limits of the second stage are such that T2 cannot be processed as long as attention is occupied by T1.9-13 The duration of the attentional blink, thus, indexes the speed of the late processing stage of visual stimuli, which is associated with perceptual awareness.12-14 Indeed, in adults, the blink only occurs if T1 is consciously perceived but not when it is missed or processed subliminally.15 Accordingly, neuroimaging studies16-18 have shown that late processes blocked by T1 involve frontoparietal areas, thought to be responsible for global cognitive availability, conscious access, and reportability.19 Here, we show that the attentional blink is present in young infants, suggesting that the two-stage organization of perception is in place at 5 and 8 months of age. In addition, we show that the duration of the attentional blink shrinks with development, suggesting that a fundamental aspect of cognitive development is the fast acceleration of the late processing stage of perception.

Consonants and vowels: different roles in early language acquisition.

Language acquisition involves both acquiring a set of words (i.e. the lexicon) and learning the rules that combine them to form sentences (i.e. syntax). Here, we show that consonants are mainly involved in word processing, whereas vowels are favored for extracting and generalizing structural relations. We demonstrate that such a division of labor between consonants and vowels plays a role in language acquisition. In two very similar experimental paradigms, we show that 12-month-old infants rely more on the consonantal tier when identifying words (Experiment 1), but are better at extracting and generalizing repetition-based srtuctures over the vocalic tier (Experiment 2). These results indicate that infants are able to exploit the functional differences between consonants and vowels at an age when they start acquiring the lexicon, and suggest that basic speech categories are assigned to different learning mechanisms that sustain early language acquisition.

Negative mental representations in infancy.

How do infants' thoughts compare to the thoughts adults express with language? In particular, can infants entertain negative representations, such as not red or not here? In four experiments, we used pupillometry to ask whether negative representations are possible without an external language. Eleven-month-olds were tested on their ability to detect and represent the abstract structure of sequences of syllables, defined by the relations identity and/or negation: AAAA (four identical syllables; Experiment 1), AAA¬A (three times the syllable A and one final syllable that is not A; Experiment 2), AA(A)(A)¬A (two-to-four times the syllable A and one final syllable that is not A; Experiment 3). Representing the structures in Experiments 2-3 requires a form of negation. Results suggest that infants are able to compute both identity and negation. More generally, these results lend credit to the hypothesis that the infant mind is equipped with rudimentary logical operators before language takes off.

Do Humans Really Learn A(n) B(n) Artificial Grammars From Exemplars?

An important topic in the evolution of language is the kinds of grammars that can be computed by humans and other animals. Fitch and Hauser (F&H; 2004) approached this question by assessing the ability of different species to learn 2 grammars, (AB)(n) and A(n) B(n) . A(n) B(n) was taken to indicate a phrase structure grammar, eliciting a center-embedded pattern. (AB)(n) indicates a grammar whose strings entail only local relations between the categories of constituents. F&H's data suggest that humans, but not tamarin monkeys, learn an A(n) B(n) grammar, whereas both learn a simpler (AB)(n) grammar (Fitch & Hauser, 2004). In their experiments, the A constituents were syllables pronounced by a female voice, whereas the B constituents were syllables pronounced by a male voice. This study proposes that what characterizes the A(n) B(n) exemplars is the distributional regularities of the syllables pronounced by either a male or a female rather than the underlying, more abstract patterns. This article replicates F&H's data and reports new controls using either categories similar to those in F&H or less salient ones. This article shows that distributional regularities explain the data better than grammar learning. Indeed, when familiarized with A(n) B(n) exemplars, participants failed to discriminate A(3) B(2) and A(2) B(3) from A(n) B(n) items, missing the crucial feature that the number of As must equal the number of Bs. Therefore, contrary to F&H, this study concludes that no syntactic rules implementing embedded nonadjacent dependencies were learned in these experiments. The difference between human linguistic abilities and the putative precursors in monkeys deserves further exploration.