The field of primate cognition studies how primates, including humans, perceive, process, store, retrieve, and use information to guide decision making and other behavior. Much of this research is motivated by a desire to understand how these abilities evolved. Large and diverse samples from a wide range of species are vital to achieving this goal. In reality, however, primate cognition research suffers from small sample sizes and is often limited to a handful of species, which constrains the evolutionary inferences we can draw. We conducted a systematic review of primate cognition research published between 2014 and 2019 to quantify the extent of this problem. Across 574 studies, the median sample size was 7 individuals. Less than 15% of primate species were studied at all, and only 19% of studies included more than one species. Further, the species that were studied varied widely in how much research attention they received, partly because a small number of test sites contributed most of the studies. These results suggest that the generalizability of primate cognition studies may be severely limited. Publication bias, questionable research practices, and a lack of replication attempts may exacerbate these problems. We describe the ManyPrimates project as one approach to overcoming some of these issues by establishing an infrastructure for large-scale collaboration in primate cognition research. Building on similar initiatives in other areas of psychology, this approach has already yielded one of the largest and most diverse primate samples to date and enables us to ask many research questions that can only be addressed through collaboration.

For over two centuries researchers have been criticized for using research practices that makes it easier to present data in line with what they wish to be true. With the rise of the internet it has become easier to preregister the theoretical and empirical basis for predictions, the experimental design, the materials, and the analysis code. Whether the practice of preregistration is valuable depends on your philosophy of science. Here, I provide a conceptual analysis of the value of preregistration for psychological science from an error statistical philosophy (Mayo, 2018). Preregistration has the goal to allow others to transparently evaluate the capacity of a test to falsify a prediction, or the severity of a test. Researchers who aim to test predictions with severity should find value in the practice of preregistration. I differentiate the goal of preregistration from positive externalities, discuss how preregistration itself does not make a study better or worse compared to a non-preregistered study, and highlight the importance of evaluating the usefulness of a tool such as preregistration based on an explicit consideration of your philosophy of science.

Anhedonia is a core symptom of major depressive disorder. Anhedonia is associated with decreased motivation to reward and with an increase in several behavioral problems such as suicide. Lempert and Pizzagalli (2010) showed that anhedonia is negatively correlated with the discounting rate in a delay discounting task. The findings of Lempert and Pizzagalli (2010) are important in revealing the relationship between anhedonia and reward sensitivity. However, the reproducibility of psychological research has recently been criticized. We conducted a replication study, based on Lempert and Pizzagalli (2010). One hundred sixty-five participants from a Japanese crowdsourcing service completed a questionnaire about anhedonia and a delay discounting task. We found that anhedonia was not significantly correlated with the delay discounting rate. We could not replicate the results of Lempert and Pizzagalli (2010). The failure to replicate the results of the aforementioned study is because of the heterogeneity of each study with regard to the delay discounting task. A meta-analysis is needed to evaluate replication and heterogeneity. Lastly, we discuss the significance of “pre-review” and “pre-registration” in the reproducibility crisis.

After Buss (1989) initiated research in the field, sex differences in individuals’ preferences for long-term mates have been extensively studied in evolutionary psychology. Numerous studies report robust sex differences such as (1) men have a stronger preference for a younger mate than do women, (2) women have a stronger preference for an older mate than do men, (3) women more highly value traits associated with resource acquisition (e.g., economic status and educational attainment) than do men, and (4) men more highly value physical attractiveness than do women. However, our replication of the study by Bech-Sørensen & Pollet (2016) did not show a significant sex difference in the preference for physical attractiveness among a Japanese sample; however, the other sex differences (e.g., age difference and resource acquisition ability) were significantly different (Study 1). We designed Study 2 to test whether the nonsignificant findings were an artifact of the item used to measure the preference for physical attractiveness. Study 2 showed that sex differences were not statistically significant. In addition, the effect of sex was significantly smaller than the pre-determined smallest effect size of interest (SESOI).

People associate emotional valence with the side of their dominant and nondominant hands. In particular, positive (or negative) valence is linked with the side of dominant (or nondominant) hand. This phenomenon is called the horizontal-valence metaphor. A previous study demonstrated that participants placed a “good” object on the side of the dominant hand and a “bad” object on the side of the nondominant hand (Casasanto, 2009, J. Exp. Psychol.: Gen, 138, 351–367). This phenomenon indicates that the horizontal-valence metaphor influences human behavior. However, later studies reported that the effect of the horizontal-valence metaphor did not occur in the other tasks. The findings of these studies raise the following question: is the effect of the horizontal-valence metaphor robust? In the present registered report, we conducted a direct replication of Experiment 1 in the Casasanto study (2009). We could not replicate the results of right-handers in the previous study. Moreover, most of the effect sizes in the present research were small, although their results were statistically significant. Our findings throw doubt on the robustness of the horizontal-valence metaphor.

In recent years, severe concerns exist regarding the replicability and reproducibility crisis of psychological research. In this special issue, to improve this situation as much as possible, we practiced “prereview of pre-registration” of the direct replication of previous research. In this paper, I summarized our practice, which was performed for the first time in Japan, through a progress report and comments by the reviewers. I also provided some perspectives for the future.

The credibility of psychological findings can be undermined by a history of questionable research practices (QRPs) by researchers. One remedy for this problem is the pre-registration of a study in which a research protocol is registered before beginning an experiment. However, the current style of pre-registration can be negatively affected by other QRPs. The purpose of this study was to demonstrate that researchers can engage in QRPs, even after a study has been preregistered. In this demonstration study, we used eight QRPs to obtain statistically meaningful results that supported an ad hoc hypothesis. Major system updates such as pre-registration, peer review, and evaluation are required to address these harmful practices. We hope that the present demonstration study provides momentum for further discussions on next-generation research practices.

In this paper, I discussed new forms of researcher evaluation in psychological research with the view of solving the reproducibility problem. I demonstrate that the current researcher evaluation system is severely biased, rather encouraging publication of less reproducible findings with fraud or bad practices. To alleviate this bias, the proposed remedies include the limitation of duplicate awards, reputation-based individual research indicators, and clarification of contributions. In addition, the evaluation by researchers from society is also biased; therefore, spins, conflicts of interest, and public involvement in research have been raised as important issues. I hope that these discussions will be noticed by interested parties who are not interested in them.

In this commentary paper, I discuss the significance of building an evidence evaluation system to evaluate the strength of evidence and the consistency between phenomena and theories in psychological science. I also discuss the usefulness of introducing the concept of “evidence level,” which is popular in evidence-based medicine. We should review the evidence-level further by referring to various external factors involving the theoretical predictability. In addition, transparency in the review process and sharing the evaluation criteria would be important.