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Developmental studies have shown that infants exploit ordinal information to extract and generalize repetition-based rules from a sequence of items. Within the visual modality, this ability is constrained by the spatial layout within which items are delivered given that a left-to-right orientation boosts infants' rule learning, whereas a right-to-left orientation hinders this ability. Infants' rule learning operates across different domains and can also be transferred across modalities when learning is triggered by speech. However, no studies have investigated whether the transfer of rule learning occurs across different domains when language is not involved. Using a visual habituation procedure, we tested 7-month-old infants' ability to extract rule-like patterns from numerical sequences and generalize them to non-numerical sequences of visual shapes and whether this ability is affected by the spatial orientation. Infants were first habituated to left-to-right or right-to-left oriented numerical sequences instantiating an ABB rule and were then tested with the familiar rule instantiated across sequences of single geometrical shapes and a novel (ABA) rule. Results showed a transfer of learning from number to visual shapes for left-to-right oriented sequences but not for right-to-left oriented ones (Experiment 1) even when the direction of the numerical change (increasing vs. decreasing) within the habituation sequences violated a small-left/large-right number-space association (Experiment 2). These results provide the first demonstration that visual rule learning mechanisms in infancy operate at a high level of abstraction and confirm earlier findings that left-to-right oriented directional cues facilitate infants' representation of order.

The ability to discriminate the ordinal information embedded in magnitude-based sequences has been shown in 4-month-old infants, both for numerical and size-based sequences. At this early age, however, this ability is confined to increasing sequences, with infants failing to extract and represent decreasing order. Here we investigate whether the ability to represent order extends to duration-based sequences in 4-month-old infants, and whether it also shows the asymmetry signature previously observed for number and size. Infants were tested in an order discrimination task in which they were habituated to either increasing or decreasing variations in temporal duration, and were then tested with novel sequences composed of new temporal items whose durations varied following the familiar and the novel orders in alternation. Across three experiments, we manipulated the duration of the single temporal items and therefore of the whole sequences, which resulted in imposing more or less constraints on infants’ working memory, or general processing capacities. Results showed that infants failed at discriminating the ordinal direction in temporal sequences when the sequences had an overall long duration (Experiment 1), but succeeded when the duration of the sequences was shortened (Experiments 2 and 3). Moreover, there was no sign of the asymmetry signature previously reported for number and size, as successful discrimination was present for infants habituated to both increasing and decreasing sequences. These results suggest that sensitivity to temporal order is present very early in development, and that its functional properties are not shared with other magnitude dimensions, such as size and number.

Early facial experience provided by the infant's social environment is known to shape face processing abilities, which narrow during the first year of life towards adult human faces of the most frequently encountered ethnic groups. Here we explored the hypothesis that natural variability in facial input may delay neural commitment to face processing by testing the impact of early natural experience with siblings on infants' brain responses. Event-Related Potentials (ERPs) evoked by upright and inverted adult and child faces were compared in two groups of 10-month-old infants with (N = 21) and without (N = 22) a child sibling. In first-born infants, P1 ERP component showed specificity to upright adult faces that carried over to the subsequent N290 and P400 components. In infants with siblings no inversion effects were observed. Results are discussed in the context of evidence from the language domain, showing that neural commitment to phonetic contrasts emerges later in bilinguals than in monolinguals, and that this delay facilitates subsequent learning of previously unencountered sounds of new languages.

Numbers are represented as ordered magnitudes along a spatially oriented number line. While culture and formal education modulate the direction of this number-space mapping, it is a matter of debate whether its emergence is entirely driven by cultural experience. By registering 8-9-month-old infants' eye movements, this study shows that numerical cues are critical in orienting infants' visual attention towards a peripheral region of space that is congruent with the number's relative position on a left-to-right oriented representational continuum. This finding provides the first direct evidence that, in humans, the association between numbers and oriented spatial codes occurs before the acquisition of symbols or exposure to formal education, suggesting that the number line is not merely a product of human invention. This work addresses the origins of the link between numbers and oriented spatial codes, as hypothesized under the'mental number line' model of numerical representation. Using a Posner-like task, we found that numerical (arrays of dots), but not non-numerical (size), cues orient 8-9 month-old infants' visual attention towards a peripheral region of space that is congruent with the number's relative position on a left-to-right oriented representational continuum. This evidence shows that a tendency to associate numbers onto spatial positions along a left-to-right oriented axis emerges before humans learn to read, write or count on their hands, and before acquisition of symbolic knowledge, supporting to the view that the number line is not merely a product of human invention.

A wealth of studies show that human adults map ordered information onto a directional spatial continuum. We asked whether mapping ordinal information into a directional space constitutes an early predisposition, already functional prior to the acquisition of symbolic knowledge and language. While it is known that preverbal infants represent numerical order along a left-to-right spatial continuum, no studies have investigated yet whether infants, like adults, organize any kind of ordinal information onto a directional space. We investigated whether 7-month-olds’ ability to learn high-order rule-like patterns from visual sequences of geometric shapes was affected by the spatial orientation of the sequences (left-to-right vs. right-to-left). Results showed that infants readily learn rule-like patterns when visual sequences were presented from left to right, but not when presented from right to left. This result provides evidence that spatial orientation critically determines preverbal infants’ ability to perceive and learn ordered information in visual sequences, opening to the idea that a left-to-right spatially organized mental representation of ordered dimensions might be rooted in biologically-determined constraints on human brain development.

Coding the direction of others' gestures is a fundamental human ability, since it allows the observer to attend and react to sources of potential interest in the environment. Shifts of attention triggered by action observation have been reported to occur early in infancy. Yet, the neurophysiological underpinnings of such action priming and the properties of gestures that might be crucial for it remain unknown. Here, we addressed these issues by recording electroencephalographic activity (EEG) from 6-month-old infants cued with spatially non-predictive hand grasping toward or away from the position of a target object, i.e., valid and invalid trials, respectively. Half of the infants were cued with a gesture executable by a human hand (possible gesture) and the other half with a gesture impossible to be executed by a human hand. Results show that the amplitude enhancement of the posterior N290 component in response to targets in valid trials, as compared to invalid trials, was present only for infants seeing possible gestures, while it was absent for infants seeing impossible gestures. These findings suggest that infants detect the biomechanical properties of human movements when processing hand gestures, relying on this information to orient their visual attention toward the target object.

Ordinality is a fundamental aspect of numerical cognition. However, preverbal infants’ ability to represent numerical order is poorly understood. In the present study we extended the evidence provided by Macchi Cassia, Picozzi, Girelli, and de Hevia (2012), showing that 4-month-old infants detect ordinal relationships within size-based sequences, to numerical sequences. In three experiments, we showed that at 4 months of age infants fail to represent increasing and decreasing numerical order when numerosities differ by a 1:2 ratio (Experiment 1), but they succeed when numerosities differ by a 1:3 ratio (Experiments 2 and 3). Critically, infants showed the same behavioral signature (i.e., asymmetry) described by Macchi Cassia et al. for discrimination of ordinal changes in area: they succeed at detecting increasing but not decreasing order (Experiments 2 and 3). These results support the idea of a common (or at least parallel) development of ordinal representation for the two quantitative dimensions of size and number. Moreover, the finding that the asymmetry signature, previously reported for size-based sequences, extends to numerosity, points to the existence of a common constraint in ordinal magnitude processing in the first months of life. The present findings are discussed in the context of possible evolutionary and developmental sources of the ordinal asymmetry, as well as their implication for other related cognitive abilities.

Recent evidence has shown that, like adults and children, 9-month-old infants manifest an operational momentum (OM) effect during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems. Here we provide the first evidence that OM occurs for transformations of non-numerical magnitudes (i.e., spatial extent) during ordering operations. Twelve-month-old infants were tested in an ordinal task in which they detected and represented ascension or descension in physical size, and then responded to ordinal sequences that exhibited greater or lesser sizes. Infants displayed longer looking time to the size change whose direction violated the operational momentum experienced during habituation (i.e., the smaller sequence in the ascension condition and the larger sequence in the descension condition). The presence of momentum for ordering size during infancy suggests that continuous quantities are represented spatially during the first year of life.

During the first year of life face discrimination abilities narrow toward adult human faces of the most frequently encountered ethnic group/s. Earlier studies showed that perceptual learning under laboratory-training protocols can modulate this narrowing process. Here we investigated whether natural experience acquired in everyday settings with an older sibling's face can shape the trajectory of perceptual narrowing towards adult faces. Using an infant-controlled habituation procedure we measured discrimination of adult (Experiment 1) and child faces (Experiment 2) in 3- and 9- month-old infants with and without a child sibling. Discrimination of adult faces was observed for infants at both ages, although accompanied by posthabituation preferences in opposite directions, whereas at both ages the discrimination of child faces critically depended on sibling experience. These results provide the first evidence that natural experience acquired with siblings affects the tuning properties of infant face representation.

The development of human body perception has long been investigated, but little is known about its early origins. This study focused on how a body part highly relevant to the human species, namely the hand, is perceived a few days after birth. Using a preferential-looking paradigm, 24- to 48-hr-old newborns watched biomechanically possible and impossible dynamic hand gestures (Experiment 1, N = 15) and static hand postures (Experiment 2, N = 15). In Experiment 1, newborns looked longer at the impossible, compared to the possible, hand movement, whereas in Experiment 2 no visual preference emerged. These findings suggest that early in life the representation of the human body may be shaped by sensory-motor experience.

The sense of touch provides fundamental information about the surrounding world, and feedback about our own actions. Although touch is very important during the earliest stages of life, to date no study has investigated infants’ abilities to process visual stimuli implying touch. This study explores the developmental origins of the ability to visually recognize touching gestures involving others. Looking times and orienting responses were measured in a visual preference task, in which participants were simultaneously presented with two videos depicting a touching and a no-touching gesture involving human body parts (face, hand) and/or an object (spoon). In Experiment 1, 2-day-old newborns and 3-month-old infants viewed two videos: in one video a moving hand touched a static face, in the other the moving hand stopped before touching it. Results showed that only 3-month-olds, but not newborns, differentiated the touching from the no-touching gesture, displaying a preference for the former over the latter. To test whether newborns could manifest a preferential visual response when the touched body part is different from the face, in Experiment 2 newborns were presented with touching/no-touching gestures in which a hand or an inanimate object—i.e., a spoon- moved towards a static hand. Newborns were able to discriminate a hand-to-hand touching gesture, but they did not manifest any preference for the object-to-hand touch. The present findings speak in favour of an early ability to visually recognize touching gestures involving the interaction between human body parts.

A large number of studies have shown that adults rely more heavily on information conveyed by the left side of the face in judging emotional state, gender and identity. This phenomenon, called left perceptual bias (LPB), suggests a right hemisphere lateralization of face processing mechanisms. Although specialization of neural mechanisms for processing over-experienced face categories begins during the first year of life, little is known about the developmental trajectory of the LPB and whether or when the bias becomes selective for specific face categories as a result of experience. To address these questions we tested adults (Experiment 1) and 5-year-old children (Experiment 2) with null or limited experience with infants in an identity matching-to-sample task with chimeric adult and infant faces, for which both adults and children have been shown to manifest differential processing abilities. Results showed that 5-year-olds manifest a leftward bias selective for adult faces, and the magnitude of the bias is larger for adult compared to infant faces in adults. This evidence is in line with earlier demonstrations of a perceptual processing advantage for adult faces in adults and children and points to the role of experience in shaping neurocognitive specialization for face processing.

Recent data demonstrate a perceptual processing advantage for adult faces in both adults and young children, suggesting that face representation is shaped by visual experience accumulated with different face-age groups. As for species and race, this age bias may emerge during the first year of life as part of the general process of perceptual narrowing, given the extensive amount of social and perceptual experience accumulated with caregivers and/or other adult individuals. Using infant-controlled habituation and visual-paired comparison at test, two experiments were carried out to examine 3- and 9-month-olds' ability to discriminate within adult and infant faces. Results showed that, when they are provided with adequate time to visually compare the stimuli during test trials (Experiment 2), 3-month-olds exhibit above-chance discrimination of adult and infant faces. Instead, 9-month-olds discriminate adult faces but not infant faces (Experiments 1 and 2). Results provide the first evidence of age-related face processing biases in infancy, and show that by 9 months face representations tune to adult human faces. © 2013 Wiley Periodicals, Inc.

Highlights • Infants’ motor system is recruited by action observation. • Infants’ motor system is involved in the anticipation of the action goal. • Infants’ motor experience affects the ability to predict the action goal. • Motor resonance mechanisms gradually develop during the first year of life., The study explores infants’ ability to generate on-line predictions about others’ action goals through the recruitment of motor resonance mechanisms. To this aim, electromyography was recorded from mouth-opening suprahyoid muscles (SM) of 9-month-old infants while watching a video of an adult agent reaching-to-grasp an object and bringing it either to mouth or head. The results demonstrated, for the first time, that at the age of 9 months there is a dynamic mirror modulation of SM activity by action observation, with the infant's muscles responsible for the action final goal being recruited from the action outset. The comparison with the responses of 6-month-olds tested on the same task showed that in younger and older infants there is a different chronometry of the SM activation with respect to the different phases of the observed action (i.e., bringing vs. grasping, respectively). Results suggest that motor resonance mechanisms triggered within the infants’ motor system by action observation undergo gradual development during the first year of life. They also indicate that motor resonance may reflect anticipation of the agent's intention based on the goal of the action.

Just like other face dimensions, age influences the way faces are processed by adults as well as by children. However, it remains unclear under what conditions exactly such influence occurs at both ages, in that there is some mixed evidence concerning the presence of a systematic processing advantage for peer faces (own-age bias) across the lifespan. Inconsistency in the results may stem from the fact that the individual's face representation adapts to represent the most predominant age traits of the faces present in the environment, which is reflective of the individual's specific living conditions and social experience. In the current study we investigated the processing of younger and older adult faces in two groups of adults (Experiment 1) and two groups of 3-year-old children (Experiment 2) who accumulated different amounts of experience with elderly people. Contact with elderly adults influenced the extent to which both adult and child participants showed greater discrimination abilities and stronger sensitivity to configural/featural cues in younger versus older adult faces, as measured by the size of the inversion effect. In children, the size of the inversion effect for older adult faces was also significantly correlated with the amount of contact with elderly people. These results show that, in both adults and children, visual experience with older adult faces can tune perceptual processing strategies to the point of abolishing the discrimination disadvantage that participants typically manifest for those faces in comparison to younger adult faces.

Previous evidence has shown that 11-month-olds represent ordinal relations between purely numerical values, whereas younger infants require a confluence of numerical and non-numerical cues. In this study, we show that when multiple featural cues (i.e., color and shape) are provided, 7-month-olds detect reversals in the ordinal direction of numerical sequences relying solely on number when non-numerical quantitative cues are controlled. These results provide evidence for the influence of featural information and multiple cue integration on infants' proneness to detect ordinal numerical information.

The current study compared the development of holistic processing for faces and non-face visual objects by testing for the composite effect for faces and frontal images of cars in 3- to 5-year-old children and adults in a series of four experiments using a two-alternative forced-choice recognition task. Results showed that a composite effect for faces was present as early as years, and none of the age groups tested showed signs of a composite effect for cars. These findings provide the first demonstration that holistic processing is already selective for faces in early childhood, and confirm existing evidence that sensitivity to holistic information in faces does not increase from 4 years to adulthood. © 2008 Blackwell Publishing Ltd.

Research has shown that experience acquired in infancy dramatically affects face-discrimination abilities. Yet much less is known about whether face processing retains any flexibility after the 1st year of life. Here, we show that early experience with an individual infant face can modulate the recognition performance of 3-year-old children and the perceptual processes they use to recognize infant faces ( Experiment 1 ). Similar experience acquired in adulthood does not produce measurable effects ( Experiment 2 ). We also show that the effects of early-acquired experience with an infant face become dormant during development in the absence of continued experience ( Experiment 3 ) and can be reactivated in adulthood by reexposure to the original experience ( Experiment 2 ). Overall, the results indicate that early experience can preserve the face-processing system from the loss of plasticity that would otherwise take place between childhood and adulthood.