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Null Hypothesis Significance Testing is a statistical procedure widely used in cognitive development research. There is widespread concern that the results of this statistical procedure are misinterpreted and lead to unsubstantiated claims about studies’ outcomes. Two particularly pertinent issues for research on cognitive development are: i) treating a non-significant result as evidence of no difference or no effect, and ii) treating a non-significant result in one group/condition and a significant result in another as evidence of a difference between groups/conditions. The current study focuses on quantifying the extent to which these two issues can be observed in the published literature on cognitive development. To this end, we will systematically search for empirical studies investigating cognitive development in 0-to-16-year-old children that have been published at two time points, namely in 1999 and 2019. For each of the two issues, we will extract information from 300 published articles, 150 per publication year.

During study design and data collection, the research of CT was supported by a grant from the Economic and Social Research Council (ESRC) (ES/K008625/1). At the time of writing, CT was supported by a grant from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement n° 714658; STONECULT project). During his work on the Dean et al. (2012) study, LGD was supported by the CULTAPTATION project (European Commission contract FP6-2004-NESTPATH-043434) and a European Research Council Advanced Grant (EVOCULTURE, 232823) awarded to Kevin Laland. The breakthrough study of Dean et al. (Science 335:1114–1118, 2012) claimed that imitation, teaching, and prosociality were crucial for cumulative cultural learning. None of their child participants solved the final stage of their puzzlebox without social support, but it was not directly tested whether the solution was beyond the reach of individual children. We provide this missing asocial control condition, showing that children can reach the final stage of the puzzlebox without social support. We interpret these findings in the light of current understanding of cumulative culture: there are currently conflicting definitions of cumulative culture, which we argue can lead to drastically different interpretations of (these) experimental results. We conclude that the Dean et al. (Science 335:1114–1118, 2012) puzzlebox fulfils a process-focused definition, but does not fulfil the (frequently used) product-focused definition. Accordingly, the precise role of social support for the apparent taxonomic distribution of cumulative culture and its ontogeny warrants further testing. Publisher PDF

To support their claim for technical reasoning skills rather than imitation as the key for cumulative technological culture (CTC), Osiurak and Reynaud argue that chimpanzees can imitate mechanical actions, but do not have CTC. They also state that an increase in working memory in human evolution could not have been a key driver of CTC. We discuss why we disagree with these claims.

Highlights • We tested a new, non-verbal working memory task in children 3–7 years of age. • Updating and manipulation were measured within a single task, the Rotating Grid Task. • Updating trials were aided by visual tracking and were easier than manipulation trials. • Manipulation trials were difficult for children across the entire age range. • The study supports evidence that manipulation has a protracted development., We developed a non-verbal task assessing updating and manipulation of working memory contents. 80 3- to 7-year-olds (47 girls; predominantly European White) were tested with a 4 × 4 grid containing 8 boxes (in the 4 centre cells and 4 outer corners). A sticker was hidden and children searched for it after a delay phase. In the updating trials, the grid was rotated during delays, in the manipulation trials, the grid was both occluded and rotated. Rewards were hidden in either the inner or outer boxes (between-subjects design). Performance was affected by age, rotation degree and hiding condition. Performance was better in outer boxes trials, where visual tracking was easier. Occluded inner trials added a substantial cognitive load (which increased with degree of rotation), resulting in children performing at chance level, suggesting that manipulation involving mental rotation is a distinct skill from tracking invisible object displacement, with a more protracted development.

In the present experiment children aged 4 and 6 years (N = 112) were read a story describing a novel supernatural agent called The Friendly Professor, who had magical powers of omniscience for behavior of those ‘in his room’ while doing ‘his experiments’. Half of the children were led to believe that this story was real, while half were told the story was fictional. Children responded to two tasks, either with a researcher present in the room, or while alone in the room. Experiment 1 comprised a two-phase overimitation task: children twice observed a series of actions on a puzzlebox modelled only at T1, then they acted on the box both immediately (T1) and again after 30-minutes (T2). Rates of overimitation did not significantly decrease over time, and overimitation was not predicted by belief/non-belief, nor by the presence/absence of the researcher. In Experiment 2 children were instructed on the rules of a ball-throwing task in which cheating was implicitly incentivized. Children were not more likely to cheat in any condition. These findings highlight the pervasiveness and persistence of overimitation, and demonstrate children’s consideration of social pressure when provided the opportunity to cheat, but not a sensitivity to the presence of supernatural figures. Our results suggest that generating supernatural belief in children - and assessing that belief - calls for more careful attention to the existing literature on children's developing understanding of special minds.

This study was supported by an Australian Research Council Discovery Project grant no. (DP140101410) awarded to M.N. At the time of writing, C.T. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 714658; STONECULT project). Through the mechanisms of observation, imitation and teaching, young children readily pick up the tool using behaviours of their culture. However, little is known about the baseline abilities of children's tool use: what they might be capable of inventing on their own in the absence of socially provided information. It has been shown that children can spontaneously invent 11 of 12 candidate tool using behaviours observed within the foraging behaviours of wild non-human apes (Reindl et al. 2016 Proc. R. Soc. B 283 , 20152402. (doi:10.1098/rspb.2015.2402)). However, no investigations to date have examined how tool use invention in children might vary across cultural contexts. The current study investigated the levels of spontaneous tool use invention in 2- to 5-year-old children from San Bushmen communities in South Africa and children in a large city in Australia on the same 12 candidate problem-solving tasks. Children in both cultural contexts correctly invented all 12 candidate tool using behaviours, suggesting that these behaviours are within the general cognitive and physical capacities of human children and can be produced in the absence of direct social learning mechanisms such as teaching or observation. Children in both cultures were more likely to invent those tool behaviours more frequently observed in great ape populations than those less frequently observed, suggesting there is similarity in the level of difficulty of invention across these behaviours for all great ape species. However, children in the Australian sample invented tool behaviours and succeeded on the tasks more often than did the Bushmen children, highlighting that aspects of a child's social or cultural environment may influence the rates of their tool use invention on such task sets, even when direct social information is absent. Publisher PDF

In 2009, Tennie et al. proposed the theory of the Zone of Latent Solutions (ZLS), defined as the range of behaviors (solutions) an individual of a species can invent independently, i.e., which it can acquire without any form of social learning. By definition, species limited to their ZLS are unable to innovate and/or transmit behavioral traits outside their ZLS, i.e., they lack traits which go beyond the level of the individual—traits resulting from a gradual cultural evolution over successive transmission events [“cumulative culture”, Boyd and Richerson (Proc Br Acad 88:73–93, 1996)]. However, this does not exclude an influence of social learning on the population frequency of these behaviors: social learning can facilitate the (ultimately individual) acquisition of latent solutions and thus speed up and consolidate their spread within a population. Cultures—defined as behaviors at least influenced by social learning—are therefore still possible (and often, even likely). Here, we elaborate on the ZLS account and relate it to the theories of Vygotsky (Mind in Society: Development of Higher Psychological Processes. Harvard University Press, 1978) who studied the role of social learning in human culture. We argue that the ZLS is a missing phylogenetic “baseline” of Vygotsky’s Zone of Actual Development (ZAD). Vygotsky’s neglect of a need for a human “baseline ZAD” (namely, a human ZLS) may have been due to his (mis-)interpretation of Kohler’s (The Mentality of Apes. Liveright, 1925) work on great ape behaviors: Kohler used his observations on individual chimpanzees to draw conclusions about the chimpanzee species as a whole, stating that chimpanzees can only copy what they could have invented themselves, thus coming close to the ZLS concept. Vygotsky—studying the range of behaviors individuals could achieve independently—seemingly did not see that Kohler was suggesting a species “baseline” (ZLS), upon which Vygotsky’s idea of an individual’s ZAD could develop. As a result, Vygotsky also did not see the need for a ZLS for his own study subjects: humans. Yet, there is no reason to assume that humans lack a ZLS, and in fact we present evidence for a human ZLS for tool-use behaviors.

Current theory-of-mind research faces the challenge of reconciling two sets of seemingly incompatible findings: Whereas children come to solve explicit verbal false belief (FB) tasks from around 4years of age, recent studies with various less explicit measures such as looking time, anticipatory looking, and spontaneous behavior suggest that even infants can succeed on some FB tasks. In response to this tension, two-systems theories propose to distinguish between an early-developing system, tracking simple forms of mental states, and a later-developing system, based on fully developed concepts of belief and other propositional attitudes. One prediction of such theories is that the early-developing system has signature limits concerning aspectuality. We tested this prediction in two experiments. The first experiment showed (in line with previous findings) that 2- and 3-year-olds take into account a protagonist's true or false belief about the location of an object in their active helping behavior. In contrast, toddlers' helping behavior did not differentiate between true and false belief conditions when the protagonist's belief essentially involved aspectuality. Experiment 2 replicated these findings with a more stringent method designed to rule out more parsimonious explanations. Taken together, the current findings are compatible with the possibility that early theory-of-mind reasoning is subject to signature limits as predicted by the two-systems account.