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Previous studies have revealed that preschoolers selectively allocate their resources based on their social relationship with recipients such as friendship. In this investigation, we investigated how expectations about recipients’ prosociality and the ability of future thinking relate to the selective allocation of resources. In Study 1, participants aged 3.5–6 years chose how to allocate resources from two ways (selfish allocation, where only the participants could receive stickers, and equal allocation, where the participants and recipients receive get the same number of stickers) in costly and non-costly situations with three recipients (friend, peer, and stranger). Participants were asked to state which alternatives the recipients would choose if they were given a choice. The results showed that children aged 5 and 6 years tended to choose equal allocation of resources when they expected the recipients to do the same both in costly and non-costly situations. This tendency was not observed in children aged 3.5 and 4 years. In Study 2, the relationships between selectivity in non-costly allocation and two facets of future thinking (delay of gratification and mental time travel) were investigated in children aged 5 and 6 years. The results suggested that children with a higher mental time travel ability tended to be more selective in allocating resources based on social relationships; they tended to allocate more resources to the friend and fewer to the peer. Our findings suggest that expectations about a recipient’s prosociality and the ability of mental time travel affect selectivity of resource allocation in children aged 5 and 6 years.

We present a new road map for research on “How the Brain Got Language” that adopts an EvoDevoSocio perspective and highlights comparative neuroprimatology – the comparative study of brain, behavior and communication in extant monkeys and great apes – as providing a key grounding for hypotheses on the last common ancestor of humans and monkeys (LCA-m) and chimpanzees (LCA-c) and the processes which guided the evolution LCA-m → LCA-c → protohumans → H. sapiens. Such research constrains and is constrained by analysis of the subsequent, primarily cultural, evolution of H. sapiens which yielded cultures involving the rich use of language.

Highly social animals possess a well-developed ability to distinguish the faces of familiar from novel conspecifics to induce distinct behaviors for maintaining society. However, the behaviors of animals when they encounter ambiguous faces of familiar yet novel conspecifics, e.g., strangers with faces resembling known individuals, have not been well characterised. Using a morphing technique and preferential-looking paradigm, we address this question via the chimpanzee's facial-recognition abilities. We presented eight subjects with three types of stimuli: (1) familiar faces, (2) novel faces and (3) intermediate morphed faces that were 50% familiar and 50% novel faces of conspecifics. We found that chimpanzees spent more time looking at novel faces and scanned novel faces more extensively than familiar or intermediate faces. Interestingly, chimpanzees looked at intermediate faces in a manner similar to familiar faces with regards to the fixation duration, fixation count, and saccade length for facial scanning, even though the participant was encountering the intermediate faces for the first time. We excluded the possibility that subjects merely detected and avoided traces of morphing in the intermediate faces. These findings suggest a bias for a feeling-of-familiarity that chimpanzees perceive familiarity with an intermediate face by detecting traces of a known individual, as 50% alternation is sufficient to perceive familiarity.

This study investigated whether lower vagal function in preterm infants is associated with increased fundamental frequency (F0 ; frequency of vocal fold vibration) of their spontaneous cries. We assessed respiratory sinus arrhythmia (RSA) during quiet sleep as a measure of vagal function, and its relationship with the F0 of spontaneous cries in healthy preterm and term infants at term-equivalent age. The results showed that preterm infants have significantly lower RSA, and higher overall F0 than term infants. Moreover, lower RSA was associated with higher overall F0 in preterm infants, whereas higher RSA was positively associated with mean and maximum F0 , and a larger F0 range in term infants. These results suggest that individual differences in vagal function may be associated with the F0 of spontaneous cries via modulation of vocal fold tension in infants at an early developmental stage.

Infant emotional expressions, such as distress cries, evoke maternal physiological reactions. Most of which involve accelerated sympathetic nervous activity. Comparatively little is known about effects of positive infant expressions, such as happy smiles, on maternal physiological responses. This study investigated how physiological and psychological maternal states change in response to infants' emotional expressions. Thirty first-time mothers viewed films of their own 6- to 7-month-old infants' affective behavior. Each observed a video of a distress cry followed by a video showing one of two expressions (randomly assigned): a happy smiling face (smile condition) or a calm neutral face (neutral condition). Both before and after the session, participants completed a self-report inventory assessing their emotional states. The results of the self-report inventory revealed no effects of exposure to the infant videos. However, the mothers in the smile condition, but not in the neutral condition, showed deceleration of skin conductance. These findings demonstrate that the mothers who observed their infants smiling showed decreased sympathetic activity. We propose that an infant's positive emotional expression may affect the branch of the maternal stress-response system that modulates the homeostatic balance of the sympathetic and parasympathetic nervous systems.

Human and nonhuman primates comprehend the actions of other individuals by detecting social cues, including others' goal-directed motor actions and faces. However, little is known about how this information is integrated with action understanding. Here, we present the ontogenetic and evolutionary foundations of this capacity by comparing face-scanning patterns of chimpanzees and humans as they viewed goal-directed human actions within contexts that differ in whether or not the predicted goal is achieved. Human adults and children attend to the actor's face during action sequences, and this tendency is particularly pronounced in adults when observing that the predicted goal is not achieved. Chimpanzees rarely attend to the actor's face during the goal-directed action, regardless of whether the predicted action goal is achieved or not. These results suggest that in humans, but not chimpanzees, attention to actor's faces conveying referential information toward the target object indicates the process of observers making inferences about the intentionality of an action. Furthermore, this remarkable predisposition to observe others' actions by integrating the prediction of action goals and the actor's intention is developmentally acquired.

Social learning in infancy is known to be facilitated by multimodal (e.g., visual, tactile, and verbal) cues provided by caregivers. In parallel with infants' development, recent research has revealed that maternal neural activity is altered through interaction with infants, for instance, to be sensitive to infant-directed speech (IDS). The present study investigated the effect of mother- infant multimodal interaction on maternal neural activity. Event-related potentials (ERPs) of mothers were compared to non-mothers during perception of tactile-related words primed by tactile cues. Only mothers showed ERP modulation when tactile cues were incongruent with the subsequent words, and only when the words were delivered with IDS prosody. Furthermore, the frequency of mothers' use of those words was correlated with the magnitude of ERP differentiation between congruent and incongruent stimuli presentations. These results suggest that mother-infant daily interactions enhance multimodal integration of the maternal brain in parenting contexts.

Human infant crying has been researched as a non-invasive tool for assessing neurophysiological states at an early developmental stage. Little is known about the acoustic features of spontaneous cries in preterm infants, although their pain-induced cries are at a higher fundamental frequency (F0) before term-equivalent age. In this study, we investigated the effects of gestational age, body size at recording and intrauterine growth retardation (IUGR) on the F0 of spontaneous cries in healthy preterm and full-term infants at term-equivalent age. We found that shorter gestational age was significantly associated with higher F0, although neither smaller body size at recording nor IUGR was related to increased F0 in preterm infants. These findings suggest that the increased F0 of spontaneous cries is not caused by their smaller body size, but instead might be caused by more complicated neurophysiological states owing to their different intrauterine and extrauterine experiences.