Kazuhide Hashiya

Development of preference for baby faces across species in humans (Homo sapiens)

Previous studies have revealed that there is a close relationship between the strength of an infant’s baby schema and the degree of its perceived cuteness. The present study investigated the development of preference for baby schema in humans by examining the recognition of the cuteness of baby faces; two studies were conducted to examine whether children’s evaluation of cuteness differed from that of adults. Facial photographs not only of humans (Homo sapiens), but a chimpanzee (Pan troglodytes), rabbits (Oryctolagus cuniculus), dogs (Canis familiaris) and cats (Felis sylvestris catus) at different ages were used as stimuli. The volunteers were requested to rank these photographs in order of cuteness. Study 1 suggested that there was a range of period during which adults perceived the faces of these five species to be the cutest. Study 2 indicated that children’s judgment of cuteness closely corresponded to that of the adults. In conclusion, the preference for baby schema is observed in humans even before they get to be sexually mature enough to reproduce. Childhood preference for baby schema might be the basis of social learning, including caretaking behaviors.

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.

Acquisition of auditory-visual intermodal matching-to-sample by a chimpanzee (Pan troglodytes): comparison with visual-visual intramodal matching

Abstract. A chimpanzee acquired an auditory—visual intermodal matching-to-sample (AVMTS) task, in which, following the presentation of a sample sound, the subject had to select from two alternatives a photograph that corresponded to the sample. The acquired AVMTS performance might shed light on chimpanzee intermodal cognition, which is one of the least understood aspects in chimpanzee cognition. The first aim of this paper was to describe the training process of the task. The second aim was to describe through a series of experiments the features of the chimpanzee AVMTS performance in comparison with results obtained in a visual intramodal matching task, in which a visual stimulus alone served as the sample. The results show that the acquisition of AVMTS was facilitated by the alternation of auditory presentation and audio-visual presentation (i.e., the sample sound together with a visual presentation of the object producing the particular sample sound). Once AVMTS performance was established for the limited number of stimulus sets, the subject showed rapid transfer of the performance to novel sets. However, the subject showed a steep decay of matching performance as a function of the delay interval between the sample and the choice alternative presentations when the sound alone, but not the visual stimulus alone, served as the sample. This might suggest a cognitive limitation for the chimpanzee in auditory-related tasks.

Hearing and Auditory-Visual Intermodal Recognition in the Chimpanzee

In contrast to the large body of studies on chimpanzee vision, few studies have examined the function of other sensory modalities in chimpanzees. In 1929, Yerkes and Yerkes noted a lack of studies on chimpanzee perception “except for the sense of sight”. The situation has remained largely unchanged for 70 years, though there are a few exceptions. Vocal-auditory functions are still the least understood behavioral pattern of chimpanzees (Mitani 1994; Nishida 1994; Tomosello and Call 1996) despite many researchers having pointed out that vocal-auditory channels play particularly important roles in behavior. Observations under completely natural conditions are not always practicable (though desirable) to evaluate the cognitive abilities of chimpanzees because of the difficulty in excluding extraneous factors. Behavioral experimentation is also needed in this sense, but there are only a limited number of studies at this point. This is probably because of the fact that training nonhuman primates in auditory-related tasks is very difficult, compared to the corresponding visual tasks.

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

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.

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.

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.

Memory for Faces in Infants: A Comparison to the Memory for Objects

Memory for faces and objects was investigated in 8- to 10-month infants. As the experience for memorizing the target face or object, face-to-face interactions between infant and experimenter in almost natural settings were conducted. To assess memory retention, two-alternative preferential looking tests were done after both a 3-minute delay and a 1-week delay from the familiarization phase. In the 3-minute delay condition, the infants looked more at the novel (not-the-experimenter) face that had not been experienced before, than the familiar (the experimenter) one. This shows that the infants memorize faces from limited experience at least for 3 minutes. On the other hand, the infants showed no such results in the object condition. These results might suggest specific processing for faces that cannot be applied for object stimuli. More detailed examinations should be done to examine this possibility