Space and rank: infants expect agents in higher position to be socially dominant.

Social hierarchies exist throughout the animal kingdom, including among humans. Our daily interactions inevitably reflect social dominance relationships between individuals. How do we mentally represent such concepts? Studies show that social dominance is represented as vertical space (i.e. high = dominant) by adults and preschool children, suggesting a space-dominance representational link in social cognition. However, little is known about its early development. Here, we present experimental evidence that 12- to 16-month-old infants expect agents presented in a higher spatial position to be more socially dominant than agents in a lower spatial position. After infants repeatedly watched the higher and lower agents being presented simultaneously, they looked longer at the screen when the lower agent subsequently outcompeted the higher agent in securing a reward object, suggesting that this outcome violated their higher-is-dominant expectation. We first manipulated agents' positions by presenting them on a podium (experiment 1). Then we presented the agents on a double-decker stand to make their spatial positions directly above or below each other (experiment 2), and we replicated the results (experiment 3). This research demonstrates that infants expect spatially higher-positioned agents to be socially dominant, suggesting deep roots of the space-dominance link in ontogeny.

Self-face perception in 12-month-old infants: A study using the morphing technique.

The present study investigated self-face perception in 12-month-old infants using the morphing technique. Twenty-four 12-month-old infants participated in both the main and control experiments. In the main experiment, we used the participant's own face, an unfamiliar infant's face (age- and gender-matched), and a morphed face comprising 50 % each of the self and unfamiliar faces as stimuli. The control experiment followed the same procedure, except that the self-face was replaced with another unfamiliar face. In both experiments, two of these stimuli were presented side by side on a monitor in each trial, and infants' fixation duration was measured. Results showed that shorter fixation durations were found for the morphed face compared with the self-face and the unfamiliar face in the main experiment, but there were no significant preferences for any comparisons in the control experiment. The results suggest that 12-month-old infants could detect subtle differences in facial features between the self-face and the other faces, and infants might show less preference for the self-resembling morphed face due to increased processing costs, which can be interpreted using the uncanny valley hypothesis. Overall, representations of the self-face seem to a certain extent to be formed by the end of the first year of life through daily visual experience.

Preverbal infants expect agents exhibiting counterintuitive capacities to gain access to contested resources.

Claims to supernatural power have been used as a basis for authority in a wide range of societies, but little is known about developmental origins of the link between supernatural power and worldly authority. Here, we show that 12- to 16-month-old infants expect agents exhibiting counterintuitive capacities to win out in a two-way standoff over a contested resource. Infants watched two agents gain a reward using either physically intuitive or physically counterintuitive methods, the latter involving simple forms of levitation or teleportation. Infants looked longer, indicating surprise, when the physically intuitive agent subsequently outcompeted a physically counterintuitive agent in securing a reward. Control experiments indicated that infants' expectations were not simply motived by the efficiency of agents in pursuing their goals, but specifically the deployment of counterintuitive capacities. This suggests that the link between supernatural power and worldly authority has early origins in development.

Overt congruent facial reaction to dynamic emotional expressions in 9-10-month-old infants.

The current study aimed to extend the understanding of the early development of spontaneous facial reactions toward observed facial expressions. Forty-six 9- to 10-month-old infants observed video clips of dynamic human facial expressions that were artificially created with morphing technology. The infants' facial responses were recorded, and the movements of the facial action unit 12 (e.g., lip-corner raising, associated with happiness) and facial action unit 4 (e.g., brow-lowering, associated with anger) were visually evaluated by multiple naïve raters. Results showed that (1) infants make congruent, observable facial responses to facial expressions, and (2) these specific facial responses are enhanced during repeated observation of the same emotional expressions. These results suggest the presence of observable congruent facial responses in the first year of life, and that they appear to be influenced by contextual information, such as the repetition of presentation of the target emotional expressions.

Phonological loop affects children's interpretations of explicit but not ambiguous questions: Research on links between working memory and referent assignment.

Understanding the referent of other's utterance by referring the contextual information helps in smooth communication. Although this pragmatic referential process can be observed even in infants, its underlying mechanism and relative abilities remain unclear. This study aimed to comprehend the background of the referential process by investigating whether the phonological loop affected the referent assignment. A total of 76 children (43 girls) aged 3-5 years participated in a reference assignment task in which an experimenter asked them to answer explicit (e.g., "What color is this?") and ambiguous (e.g., "What about this?") questions about colorful objects. The phonological loop capacity was measured by using the forward digit span task in which children were required to repeat the numbers as an experimenter uttered them. The results showed that the scores of the forward digit span task positively predicted correct response to explicit questions and part of the ambiguous questions. That is, the phonological loop capacity did not have effects on referent assignment in response to ambiguous questions that were asked after a topic shift of the explicit questions and thus required a backward reference to the preceding explicit questions to detect the intent of the current ambiguous questions. These results suggest that although the phonological loop capacity could overtly enhance the storage of verbal information, it does not seem to directly contribute to the pragmatic referential process, which might require further social cognitive processes.

Observing Third-Party Attentional Relationships Affects Infants' Gaze Following: An Eye-Tracking Study.

Not only responding to direct social actions toward themselves, infants also pay attention to relevant information from third-party interactions. However, it is unclear whether and how infants recognize the structure of these interactions. The current study aimed to investigate how infants' observation of third-party attentional relationships influence their subsequent gaze following. Nine-month-old, 1-year-old, and 1.5-year-old infants (N = 72, 37 girls) observed video clips in which a female actor gazed at one of two toys after she and her partner either silently faced each other (face-to-face condition) or looked in opposite directions (back-to-back condition). An eye tracker was used to record the infants' looking behavior (e.g., looking time, looking frequency). The analyses revealed that younger infants followed the actor's gaze toward the target object in both conditions, but this was not the case for the 1.5-year-old infants in the back-to-back condition. Furthermore, we found that infants' gaze following could be negatively predicted by their expectation of the partner's response to the actor's head turn (i.e., they shift their gaze toward the partner immediately after they realize that the actor's head will turn). These findings suggested that the sensitivity to the difference in knowledge and attentional states in the second year of human life could be extended to third-party interactions, even without any direct involvement in the situation. Additionally, a spontaneous concern with the epistemic gap between self and other, as well as between others, develops by this age. These processes might be considered part of the fundamental basis for human communication.

Pointing behavior in infants reflects the communication partner's attentional and knowledge states: a possible case of spontaneous informing.

Inferring the epistemic states of others is considered to be an essential requirement for humans to communicate; however, the developmental trajectory of this ability is unclear. The aim of the current study was to determine developmental trends in this ability by using pointing behavior as a dependent measure. Infants aged 13 to 18 months (n = 32, 16 females) participated in the study. The experiment consisted of two phases. In the Shared Experience Phase, both the participant and the experimenter experienced (played with) an object, and the participant experienced a second object while the experimenter was absent. In the Pointing Phase, the participant was seated on his/her mother's lap, facing the experimenter, and the same two objects from the Shared Experience Phase were presented side-by-side behind the experimenter. The participants' spontaneous pointing was analyzed from video footage. While the analysis of the Shared Experience Phase suggested that there was no significant difference in the duration of the participants' visual attention to the two objects, the participants pointed more frequently to the object that could be considered "new" for the experimenter (in Experiment 1). This selective pointing was not observed when the experimenter could be considered unfamiliar with both of the objects (in Experiment 2). These findings suggest that infants in this age group spontaneously point, presumably to inform about an object, reflecting the partner's attentional and knowledge states.

Development of reference assignment in children: a direct comparison to the performance of cognitive shift.

The referent of a deictic embedded in a particular utterance or sentence is often ambiguous. Reference assignment is a pragmatic process that enables the disambiguation of such a referent. Previous studies have demonstrated that receivers use social-pragmatic information during referent assignment; however, it is still unclear which aspects of cognitive development affect the development of referential processing in children. The present study directly assessed the relationship between performance on a reference assignment task (Murakami and Hashiya, in preparation) and the dimensional change card sort task (DCCS) in 3- and 5-years-old children. The results indicated that the 3-years-old children who passed DCCS showed performance above chance level in the event which required an explicit (cognitive) shift, while the performance of the children who failed DCCS remained in the range of chance level; however, such a tendency was not observed in the 5-years-old, possibly due to a ceiling effect. The results indicated that, though the development of skills that mediate cognitive shifting might adequately explain the explicit shift of attention in conversation, the pragmatic processes underlying the implicit shift, which requires reference assignment, might follow a different developmental course.

Minocycline, a microglial inhibitor, reduces 'honey trap' risk in human economic exchange.

Recently, minocycline, a tetracycline antibiotic, has been reported to improve symptoms of psychiatric disorders and to facilitate sober decision-making in healthy human subjects. Here we show that minocycline also reduces the risk of the 'honey trap' during an economic exchange. Males tend to cooperate with physically attractive females without careful evaluation of their trustworthiness, resulting in betrayal by the female. In this experiment, healthy male participants made risky choices (whether or not to trust female partners, identified only by photograph, who had decided in advance to exploit the male participants). The results show that trusting behaviour in male participants significantly increased in relation to the perceived attractiveness of the female partner, but that attractiveness did not impact trusting behaviour in the minocycline group. Animal studies have shown that minocycline inhibits microglial activities. Therefore, this minocycline effect may shed new light on the unknown roles microglia play in human mental activities.

Minocycline modulates human social decision-making: possible impact of microglia on personality-oriented social behaviors.

BACKGROUND: Microglia, one of the glial cells, play important roles in various brain pathologies including psychiatric disorders. In addition, microglia have recently been proved to monitor synaptic reactions via direct-touching even in normal brain. Human microglia may modulate various social/mental functions, while microglial social/mental roles remain unresolved especially in healthy humans. There is no known drug with the specific effect of modulating microglia. Therefore, using minocycline, a tetracycline antibiotic and the most famous microglial inhibitor, is one of the best alternative approaches to clarify microglial functions on human social/mental activities. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a double-blind randomized trial of trust game, a monetary decision-making experiment, with ninety-nine human adult males who decided how much to trust an anonymous partner after a four-day administration of minocycline. Our previous pilot trial indicated a positive effect of minocycline, while the underlying mechanisms were not clarified. Therefore, in this trial with larger samples, we additionally measured the effects of anxiety and personality. The monetary score in trust game was significantly lower in the minocycline group. Interestingly, participants' ways of decision-making were significantly shifted; cooperativeness, one component of personality, proved to be the main modulating factor of decision-making in the placebo group, on the other hand, the minocycline group was mainly modulated by state anxiety and trustworthiness. CONCLUSIONS/SIGNIFICANCE: Our results suggest that minocycline led to more situation-oriented decision-making, possibly by suppressing the effects of personality traits, and furthermore that personality and social behaviors might be modulated by microglia. Early-life events may activate human microglia, establish a certain neuro-synaptic connection, and this formation may determine each human's personality and personality- oriented social behaviors in later life. To explore these mechanisms, further translational research is needed. TRIAL REGISTRATION: UMIN clinical trial center UMIN000004803.

Preference for consonant music over dissonant music by an infant chimpanzee.

It has been shown that humans prefer consonant sounds from the early stages of development. From a comparative psychological perspective, although previous studies have shown that birds and monkeys can discriminate between consonant and dissonant sounds, it remains unclear whether nonhumans have a spontaneous preference for consonant music over dissonant music as humans do. We report here that a five-month-old human-raised chimpanzee (Pan troglodytes) preferred consonant music. The infant chimpanzee consistently preferred to produce, with the aid of our computerized setup, consonant versions of music for a longer duration than dissonant versions. This result suggests that the preference for consonance is not unique to humans. Further, it supports the hypothesis that one major basis of musical appreciation has some evolutionary origins.

A non-humanoid robot in the "uncanny valley": experimental analysis of the reaction to behavioral contingency in 2-3 year old children.

Infants' sensitivity to social or behavioral contingency has been examined in the field of developmental psychology and behavioral sciences, mainly using a double video paradigm or a still face paradigm. These studies have shown that infants distinguish other individuals' contingent behaviors from non-contingent ones. The present experiment systematically examined if this ability extends to the detection of non-humanoids' contingent actions in a communicative context. We examined two- to three-year-olds' understanding of contingent actions produced by a non-humanoid robot. The robot either responded contingently to the actions of the participants (contingent condition) or programmatically reproduced the same sequence of actions to another participant (non-contingent condition). The results revealed that the participants exhibited different patterns of response depending on whether or not the robot responded contingently. It was also found that the participants did not respond positively to the contingent actions of the robot in the earlier periods of the experimental sessions. This might reflect the conflict between the non-humanlike appearance of the robot and its humanlike contingent actions, which presumably led the children to experience the uncanny valley effect.

Detection of the relevant type of locomotion in infancy: crawlers versus walkers.

Human infants show a preference for individuals who are similar to them. Using point-light displays of human walkers and crawlers as stimuli, we examined whether infants' preference for the motions of crawling and walking changes between, before, and after the onset of bipedal walking. The results show that crawling and walking infants prefer the types of locomotion that are similar to their own, respectively. These indicate that the infants detect the similarities between the motions they performed and they observed, which provides the behavioral evidence that the production of a particular motion is connected to its perception in infancy.

Preference for peers in infancy.

Previous findings suggest that infants prefer other infants from among individuals of various ages. There are two explanations for this: one is that like adults, infants prefer babyish characteristics; the other is that infants prefer individuals who are similar to themselves. We examined whether infants respond differently to same-age infants from among older or younger infants. This might allow the possibility of methodologically separating the two explanations for peer preference in infancy. The results revealed that 9-month-olds showed peer preference when they saw movies of infants. Further experiments showed that 6- and 9-month-olds preferred static images of same-age infants. The lack of preference of 6-month-olds for movies of same-age infants could be related to their ability to process information. Thus, the cue for peer preference may be physical similarity to oneself, rather than the strength of babyish characteristics reflecting a particular developmental stage.