Comparative studies on cognitive development in primates including humans provide deeper insights to understand the evolutionary origins of cognitive development in human children. Primatology in Japan has the long history of publishing research achievements in international academic societies from the beginning. This report summarized the comparative studies on cognitive development in chimpanzees by focusing on object manipulation as a non-verbal comparative scale. Direct comparison between chimpanzees and human children revealed fundamental similarities in some tasks testing their ability of performing combinatory manipulation which is a prerequisite of the tool-using behavior. However, human children performed better in a task requiring social referencing during object manipulation. Efforts for expanding the study theme to other great apes which has relatively limited developmental data and to other cognitive functions outside the object-manipulation context are also reported as well as the importance of mother-infant interactions as a foundation of cognitive development. Studies on chimpanzees, as an ultimately different culture, gives us clues for promoting international outputs from Japanese studies in the domain of comparative cognitive development.

When we consider a significance of international research outcomes, it depends on individual thoughts and there may be various motivations and reasons. Some researchers may advocate the uniqueness of Japanese children, other researchers may suggest the cultural difference. However, the authors have continued to submit our own studies to international journals based on the simple motivation to survive against international competition. First, we review our international infant studies which we have submitted to international journals. Specifically, we introduce empirical experiments of social cognitive development that investigate understanding others, moral/prosocial behaviors, and social learning in early infancy. Then, we discuss the personal significance and its challenge of international research outcomes, which we have acquired in the process of international competition, and then think about the future of Japanese developmental psychology.

This article gives an overview of the author's research on development of mental state understanding and interpersonal communication, and discusses the significance of disseminating developmental psychology from Japan to the world. First, it describes a review of two studies on Japanese children's understanding of apparent crying, and two studies on Japanese and Italian children's sensitivity to teacher and peer criticism, focusing on the development of children's theory of mind. An examination of these studies indicated the need to pay attention to the various social contexts in which child development is embedded when we try to capture the development of mental state understanding and social interaction. It also revealed the difficulty in capturing a holistic picture of Japanese children's development using Western perspectives and research paradigms. Future directions for disseminating the findings of Japanese developmental psychology worldwide are discussed.

The internationalization of developmental research in Japan has progressed in recent years, with many Japanese research papers having been published in international journals in English. However, the submission of scientific papers to international journals is not necessarily the optimal choice in the field of psychology in Japan. The authors have continued to make presentations at international conferences regarding the results of developmental psychology studies based on an interdisciplinary approach that goes beyond traditional confines. Here we introduce the authors' developmental research on the effects of others observing altruistic behavior in children, alongside our rationale for selecting this theme in the context of developmental research from Japan. Finally, the authors state their informed opinion regarding the significance of international research dissemination and the prospects of developmental psychology in Japan.

The purpose of this paper is to consider how to pave the way for research dialog toward the world. For this, I considered the cross-border perspective of the concept of “adaptation” along the three axes of “academic field/ genre,” “country/region,” and “period/time” and examined what kind of image of adaptation emerged. A framework for reexamining this concept, used, for example, in developmental psychology, from a multifaceted perspective was indicated. Through such conceptual and theoretical examination I tried to gain a fresh understanding of adaptation. The study clarified that, adaptation, constitutes an issue of agency, is not at all a self-evident concept, can include both changes of humans themselves and external circumstances (physical and social environment), and, there are forms of adaptation that do not become visible just by living in a specific country/region or a specific era/time. Finally, I highlight that our attempt involves a research dialog toward the world and examine how the research results of developmental psychology can be oriented to the world and broadened through dialog.

In this article, we consider the meaning of communicating Japanese developmental research to the world, and propose some concrete suggestions. Concretely, we pick up and summarize some characteristics and uniqueness of Japanese studies, based principally on the Japanese Journal de Developmental Psychology. Firstly, we outline the methodological strong points of Japanese developmental researches, as the development of quantitative and qualitative methods, the proportion of longitudinal studies, and the debates on the individual difference in development. Secondly, we present some examples of studies, for their originality of behavioral indicators, or choice of activities as salient context. Thirdly, from the viewpoint of cultural comparative psychology, we summarize the uniqueness and benefits of Japanese developmental studies, and discuss them including generational and historical changes. Behind these characteristics, the epistemological conception of Japanese researchers is certainly involved. Finally, concrete proposals for facilitating the communication of Japanese developmental research to the world are summarized.

The internationalization of study of development in Japan and contributions to international society has been an issue for a long time. In this study, based on three symposiums held in the 2017 Conference of the Japan Society of Developmental Psychology, the internationalization of studies of development is discussed from the following three perspectives. The first examines cultural dependency of study of development from the viewpoints of developmental research from Europe and America (especially English-speaking countries), the second examines the current status in internationalization by Japanese researchers and the academic trends of studies of development, based on high-quality cases of development studies, and the third examines the role and potential of the Japan Society of Developmental Psychology and the association's journal and considers the possibilities of supporting researchers toward internationalization. Finally, this paper discusses what should lie at the root of studies that tend to be overlooked by researchers aiming for internationalization.

This study examined the longitudinal effects of paternal depression in the context of the family system based on findings on the relational mechanism obtained in the previous study (author, 2016b). Data were collected from both mothers and fathers of 135 children attending 12 different kindergartens in the Tokyo metropolitan area. Surveys were conducted when the children were three and five years old. The causal relation between paternal depression and father–child relationships and paternal depression and parental relationships were investigated using a cross-lagged effects model. Results revealed that paternal depression negatively affected the quality of father–child relationships as well as parental relationships, both of which were measured through self-reports by fathers. Findings suggest that paternal depression has a detrimental effect on fathers' perception of the quality of family relationships. This study has confirmed the importance of considering paternal depression in early childhood and the need to also consider its influence on family members.

The purpose of this study is to examine the process and characteristics of teachers' involvement and difficulties with children with ADHD tendencies in regular classrooms. Semi-structured interviews were conducted with 16 elementary school teachers and were analyzed using the grounded theory approach. This resulted in eight category groups. Then, a hypothesis model was generated. When improvement is not seen in [situations of adaptive difficulties], [teacher distress] arose. Next, the teachers developed a multidimensional understanding of the children by [understanding the characteristics] of the children's behavior and cognition and [understanding the children] in terms of their inner world; involvement under this new viewpoint was organized through the [re-examination of responses]. Based on these results, the involvements that seemed to be useful for the children with ADHD tendencies in regular classrooms were arranged as (a) direct involvement with children, (b) involvement with the environment, and (c) multidimensional understanding of the children; then, educational suggestions were presented. Finally, meanings of the difficulties for teachers were considered.

From the perspective of the dynamic systems approach, previous studies have redefined motor development theory, and movement variability has been an essential evaluation index for analyzing motor development. Accordingly, this study investigated the characteristics of motor development in a child with autism spectrum disorder (ASD) focusing on movement variability. The child's jumping movements were analyzed using a longitudinal design that incorporated multiple time scales. Results indicate that the child with ASD made a total of 129 variable jumping movements during the 13 months of the study. These variable movements were seen to alternate between the stability and instability aspects. Furthermore, qualitative changes in his jumping movements occurred in response to changing task constraints, that is, - primarily, the way he cared about his own body or external constraints. These findings suggest that for children with ASD, adapting to task constraints is a critical factor for increasing movement variability and long-term motor development.