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Mirror self-recognition (MSR) is considered to be the benchmark of objective self-awareness--the ability to think about oneself. Cross-cultural research showed that there are systematic differences in toddlers' MSR abilities between 18 and 24 months. Understanding whether these differences result from systematic variation in early social experiences will help us understand the processes through which objective self-awareness develops. In this study, we examined 57 18- to 22-month-old toddlers (31 girls) and their mothers from two distinct sociocultural contexts: urban Canada (58% of the sub-sample were Canadian-born native English-speakers) and rural Vanuatu, a small-scale island society located in the South Pacific. We had two main goals: (a) to identify the social-interactional correlates of MSR ability in this cross-cultural sample, and (b) to examine whether differences in passing rates could be attributed to confounding factors. Consistent with previous cross-cultural research, ni-Vanuatu toddlers passed the MSR test at significantly lower rates (7%) compared to their Canadian counterparts (68%). Among a suite of social interactive variables, only mothers' imitation of their toddlers' behavior during a free play session predicted MSR in the entire sample and maternal imitation partially mediated the effects of culture on MSR. In addition, low passing rates among ni-Vanuatu toddlers could not be attributed to reasons unrelated to self-development (i.e., motivation to show mark-directed behavior, understanding mirror-correspondence, representational thinking). This suggests that differences in MSR passing rates reflect true differences in self-recognition, and that parental imitation may have an important role in shaping the construction of visual self-knowledge in toddlers. [ABSTRACT FROM AUTHOR]

We examine the opportunities children have for interacting with others and the extent to which they are the focus of others' visual attention in five societies where extended family communities are the norm. We compiled six video-recorded datasets (two from one society) collected by a team of anthropologists and psychologists conducting long-term research in each society. The six datasets include video observations of children among the Yasawas (Fiji), Tanna (Vanuatu), Tsimane (Bolivia), Huatasani (Peru), and Aka (infants and children 4–12 years old; Central African Republic). Each dataset consists of a series of videos of children ranging in age from 2 months to 12 years in their everyday contexts. We coded 998 videos and identified with whom children had opportunities to interact (male and female adults and children) as well as the number of individuals and the proportion of observed time that children spent with these individuals. We also examined the proportion of time children received direct visual gaze (indicating attention to the child). Our results indicate that children less than 5 years old spend the majority of their observed time in the presence of one female adult. This is the case across the five societies. In the three societies from which we have older children (Aka, Yasawa, Peru), we find a clear shift around 5 years of age, with children spending the majority of their time with other children. We also coded the presence or absence of a primary caregiver and found that caregivers remained within 2 ft of target children until 7 years of age. When they were in the company of a primary caregiver, children older than seven spent the majority of their time more than 2 ft from the caregiver. We found a consistent trend across societies with decreasing focal attention on the child with increasing child age. These findings show (1) remarkable consistency across these societies in children's interaction opportunities and (2) that a developmental approach is needed to fully understand human development because the social context is dynamic across the lifespan. These data can serve as a springboard for future research examining social development in everyday contexts. [ABSTRACT FROM AUTHOR]

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour. [ABSTRACT FROM AUTHOR]

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour. [ABSTRACT FROM AUTHOR]

When speaking to infants, mothers often alter their speech compared to how they speak to adults, but findings for fathers are mixed. This study examined interactions (N = 30) between fathers and infants (Mage  ± SD = 7.8 ± 4.3 months) in a small-scale society in Vanuatu and two urban societies in North America. Fundamental frequency (F0 ) and speech rate were measured in infant-directed and adult-directed speech. When speaking to infants, fathers in both groups increased their F0 range, yet only Vanuatu fathers increased their average F0 . Conversely, North American fathers slowed down their speech rate to infants, whereas Vanuatu fathers did not. Behavioral traits can vary across distant cultures while still potentially solving similar communicative problems. [ABSTRACT FROM AUTHOR]

Humans are unique in their propensity for helping. Not only do we help others in need by reacting to their requests, we also help proactively by assisting in the absence of a request. Proactive helping requires the actor to detect the need for help, recognize the intention of the other, and remedy the situation. Very little is known about the development of this social phenomenon beyond an urban, industrialized setting. We examined helping in nineteen two- to five-year old children in small-scale rural villages of Vanuatu. In the experimental condition, the intentions of the experimenter were made salient, whereas in the control condition they were ambiguous. Children helped more often in the experimental compared to the control condition, suggesting that the propensity to monitor others’ goals and act accordingly can be detected in different cultural contexts. [ABSTRACT FROM AUTHOR]

The first relationship between an infant and her caregiver, typically the mother, lays the foundation for cognitive, social, and emotional development. Maternal responsiveness and affect mirroring have been studied extensively in Western societies yet very few studies have systematically examined these caregiving features in non-Western settings. Sixty-six mother-infant dyads (7 months, SD = 3.1) were observed in a small-scale, rural island society in Fiji, a village in Kenya, and an urban center in the United States. Mothers responded similarly to infant bids overall, but differences were found across societies in the ways mothers selectively respond to affective displays. This has implications for understanding early emotion socialization as well as understanding variation in infant social ecologies across the globe. [ABSTRACT FROM AUTHOR]

Humans are extraordinarily prosocial, and research conducted primarily in North America indicates that giving to others is emotionally rewarding. To examine whether the hedonic benefits of giving represent a universal feature of human behavior, we extended upon previous cross-cultural examinations by investigating whether inhabitants of a small-scale, rural, and isolated village in Vanuatu, where villagers have little influence from urban, Western culture, survive on subsistence farming without electricity, and have minimal formal education, report or display emotional rewards from engaging in prosocial (vs. personally beneficial) behavior. In Study 1, adults were randomly assigned to purchase candy for either themselves or others and then reported their positive affect. Consistent with previous research, adults purchasing goods for others reported greater positive emotion than adults receiving resources for themselves. In Study 2, 2- to 5-year-old children received candy and were subsequently asked to engage in costly giving (sharing their own candy with a puppet) and non-costly giving (sharing the experimenter's candy with a puppet). Emotional expressions were video-recorded during the experiment and later coded for happiness. Consistent with previous research conducted in Canada, children displayed more happiness when giving treats away than when receiving treats themselves. Moreover, the emotional rewards of giving were largest when children engaged in costly (vs. non-costly) giving. Taken together, these findings indicate that the emotional rewards of giving are detectable in people living in diverse societies and support the possibility that the hedonic benefits of generosity are universal. [ABSTRACT FROM AUTHOR]

Literature on infant emotion is dominated by research conducted in Western, industrialized societies where early socialization is characterized by face-to-face, vocal communication with caregivers. There is a dearth of knowledge of infant emotion in the context of social interaction outside of the visual and vocal modalities. In a three-population cross-cultural comparison, we used the still-face task to measure variation in behavior among infants from proximal care (practicing high levels of physical contact) communities in Bolivia and distal care (emphasizing vocal and visual interaction) communities in the U.S. and Fiji. In a modified version of the face-to-face still-face (FFSF), Study 1, infants in the U.S. and Fiji displayed the typical behavioral response to the still-face episode: increased negative affect and decreased social engagement, whereas infants in Bolivia showed no change. For tactile behavior, infants in Bolivia showed an increase in tactile self-stimulation from the interaction episode to the still-face episode, whereas U.S. infants showed no change. In Study 2, we created a novel body-to-body version of the still-face paradigm ("still-body") with infants in US and Bolivia, to mimic the near-constant physical contact Bolivian infants experience. The U.S. and Bolivian infant response was similar to Study 1: US infants showed decreased positive affect and increased negative affect and decreased social engagement from the interaction to the still-body episode and Bolivian infants showed no change. Notably, there were overall differences in infant behaviors between the two paradigms (FFSF and Still-Body). Infants in Bolivia and the U.S. showed increased positive facial affect during the FFSF paradigm in comparison with the Still-Body paradigm. Our results demonstrate the need for more globally representative developmental research and a broader approach to infant emotion and communication. [ABSTRACT FROM AUTHOR]

Abstract: Self-recognition by 86 children (14–52months) was assessed using the mirror mark test in two different social contexts. In the classic mirror task condition, only the child was marked prior to mirror exposure (Classic condition). In the social norm condition, the child, experimenter, and accompanying parent were marked prior to the child’s mirror exposure (Norm condition). Results indicate that in both conditions children pass the test in comparable proportion, with the same increase as a function of age. However, in the Norm condition, children displayed significantly more hesitation while removing the mark, often touching it without removing it or, if so, promptly putting the mark back onto their forehead. In the Classic condition, only one child showed such hesitation. These results suggest that from the outset, mirror self-recognition can refer to social awareness. This link is interpreted as the trademark of human self-consciousness, a deeply rooted “looking glass” self-awareness. [Copyright &y& Elsevier]

Humans are extraordinary in the extent to which we rely on cumulative culture to act upon and make sense of our environment. Teaching is one social learning process thought to be fundamental to the evolution of cumulative culture as a means of adaptation in our species. However, the frequency of teaching and how we teach are known to vary across human sociocultural contexts. Understanding this variation adds to our understanding of the complex interplay between cognition and culture in shaping learning behavior but also contributes to theory around the costs and benefits of different social learning processes. Here, we examined how prior experience with formal education is related to the frequency and diversity of teaching behaviors in an experimental paradigm where caregivers were motivated (but not instructed) to teach a simple skill to a child (7–10 years old). We identified and coded a suite of subtle nonverbal behaviors that could be construed as facilitating learning. Dyads (n = 64) were recruited from two communities on Tanna Island that differ in their experience with formal schooling and their acceptance of Western institutions. We found evidence for parallel teaching strategies in both communities. However, the rate and diversity of teaching behaviors were positively associated with caregiver's experience with formal schooling and independently and negatively associated with being from a village that rejects Western-derived institutions. These results further our understanding of how multiple cultural processes influence social learning and highlights the powerful influence of formal schooling on the cultural evolution of teaching in humans. [ABSTRACT FROM AUTHOR]

The authors examined similarities and differences in Canadian and ni‐Vanuatu caregivers' child‐directed speech to their toddlers (N = 35, Mage: 21 months, 20 girls). Speech samples were collected (2013–2016) during free play and analyzed with a focus on describing parents' references to their toddlers. Canadian caregivers referred significantly more to toddlers' tangible characteristics (relative risk, RR = 2.12) and internal states (RR = 2.31), whereas ni‐Vanuatu caregivers referred more to actions (RR = 2.04). When referring to internal states, Canadian mothers referred significantly more to mind‐minded states, whereas ni‐Vanuatu caregivers referred more to body‐minded states (RR = 7.98). These findings are interpreted as capturing meaningful differences in toddlers' opportunities to attend to themselves. Implications for self‐concept development are discussed. [ABSTRACT FROM AUTHOR]

Infant‐directed speech (IDS) is phonetically distinct from adult‐directed speech (ADS): It is typically considered to have special prosody—like higher pitch and slower speaking rates—as well as unique speech sound properties, for example, more breathy, hyperarticulated, and/or variable consonant and vowel articulation. These phonetic features are widely observed in the IDS of caregivers from urbanized contexts who speak a handful of very well‐researched languages. Yet studies with more diverse socio‐cultural and linguistic samples show that this "typical" IDS prosody is not consistently observed across cultures. We extended cross‐cultural work by examining IDS speech segment articulation, which—like prosody—is also thought to be a characteristic phonetic feature of IDS that might aid speech and language development. Here we asked whether IDS vowels have different articulatory features compared to ADS vowels in two distinct linguistic and socio‐cultural contexts: urban English‐speaking Canadian mothers, and rural Lenakel‐ and Southwest Tanna‐speaking ni‐Vanuatu mothers (n = 57, 20–46 years of age). Replicating prior work, Canadian mothers had more variable vowels in IDS compared to ADS, but also did not show clear register differences for breathiness or hyperarticulation. Vowels spoken by ni‐Vanuatu mothers showed very distinct articulatory tendencies, using less variable (and less breathy) IDS vowels. Along with other work showing diversity in IDS phonetics across populations, this paper suggests that any understanding of how IDS might aid speech and language development are best examined through a culturally‐ and linguistically‐specific lens. [ABSTRACT FROM AUTHOR]

Gaze is considered a crucial component of early communication between an infant and her caregiver. When communicatively addressed, infants respond aptly to others' gaze by following its direction. However, experience with face‐to‐face contact varies across cultures, begging the question whether infants' competencies in receiving others' communicative gaze signals are universal or culturally specific. We used eye‐tracking to assess gaze‐following responses of 5‐ to 7‐month olds in Vanuatu, where face‐to‐face parent–infant interactions are less prevalent than in Western populations. We found that—just like Western 6‐month‐olds studied previously—5‐ to ‐7‐month‐olds living in Vanuatu followed gaze only, when communicatively addressed. That is, if presented gaze shifts were preceded by infant‐directed speech, but not if they were preceded by adult‐directed speech. These results are consistent with the notion that early infant gaze following is tied to infants' early emerging communicative competencies and rooted in universal mechanisms rather than being dependent on cultural specificities of early socialization. [ABSTRACT FROM AUTHOR]

It is known that infant‐directed speech (IDS) plays a key role in language development. Previous research, however, has also identified significant variability across societies in terms of how often IDS occurs. For example, some studies report very little IDS in non‐western, small‐scale societies – including children growing up in small‐scale societies in Tanna, Vanuatu. This is surprising given that IDS is widely assumed as a common feature of human caregiving based on research conducted in urbanised populations which are more well‐studied. Here, we propose that IDS is only one of a suite of important caregiving behaviours that are produced during interactions with infants, which may vary by culture, perhaps being replaced by other, non‐verbal infant‐directed behaviours (IDB). We will examine previously collected data consisting of 94 semi‐structured 10‐min video observations of caregivers and their 18–24 month‐old children in rural Tanna, Vanuatu and urban Vancouver, Canada to identify and compare the proportion of time caregivers spend engaging in IDS and IDB during these interactions, both within and between societies. We define IDS as caregiver speech or vocalisations during the interaction with the infant, and we define IDB as non‐verbal behaviours that are produced with the infant during the interaction. This study aims to take a step towards a more generalised understanding of language development in children, moving beyond the urban and western societies in which our understanding of development is currently based, and the predicted results will aid in recognising different developmental pathways within multi‐cultural communities. [ABSTRACT FROM AUTHOR]

It is widely held that intuitive dualism—an implicit default mode of thought that takes minds to be separable from bodies and capable of independent existence—is a human universal. Among the findings taken to support universal intuitive dualism is a pattern of evidence in which "psychological" traits (knowledge, desires) are judged more likely to continue after death than bodily or "biological" traits (perceptual, physiological, and bodily states). Here, we present cross‐cultural evidence from six study populations, including non‐Western societies with diverse belief systems, that shows that while this pattern exists, the overall pattern of responses nonetheless does not support intuitive dualism in afterlife beliefs. Most responses of most participants across all cultures tested were not dualist. While our sample is in no way intended to capture the full range of human societies and afterlife beliefs, it captures a far broader range of cultures than in any prior study, and thus puts the case for afterlife beliefs as evidence for universal intuitive dualism to a strong test. Based on these findings, we suggest that while dualist thinking is a possible mode of thought enabled by evolved human psychology, such thinking does not constitute a default mode of thought. Rather, our data support what we will call intuitive materialism—the view that the underlying intuitive systems for reasoning about minds and death produce as a default judgment that mental states cease to exist with bodily death. [ABSTRACT FROM AUTHOR]

We examined infant activity level and attention in 45 eight‐month‐old infants (mean age 8.8, SD = 2.07) living in two diverse socio‐cultural contexts: rural island societies in the South Pacific and urban Western societies in North America. Infants and mothers were observed for 10 minutes in a face‐to‐face interaction and later coded for the frequency of infants' motor movements and gaze shifts. Results indicate that infants in urban North American societies produced more frequent motor movements and gaze shifts compared to infants in rural, island societies in Oceania. We interpret these discrepancies as reflecting differences in social experience, ecological niches as well as physiological experiences. These findings highlight the complex interplay of development and experience early in life. [ABSTRACT FROM AUTHOR]

Culture is a human universal, yet it is a source of variation in human psychology, behaviour and development. Developmental researchers are now expanding the geographical scope of research to include populations beyond relatively wealthy Western communities. However, culture and context still play a secondary role in the theoretical grounding of developmental psychology research, far too often. In this paper, we highlight four false assumptions that are common in psychology, and that detract from the quality of both standard and cross-cultural research in development. These assumptions are: (i) the universality assumption, that empirical uniformity is evidence for universality, while any variation is evidence for culturally derived variation; (ii) the Western centrality assumption, that Western populations represent a normal and/or healthy standard against which development in all societies can be compared; (iii) the deficit assumption, that population-level differences in developmental timing or outcomes are necessarily due to something lacking among non-Western populations; and (iv) the equivalency assumption, that using identical research methods will necessarily produce equivalent and externally valid data, across disparate cultural contexts. For each assumption, we draw on cultural evolutionary theory to critique and replace the assumption with a theoretically grounded approach to culture in development. We support these suggestions with positive examples drawn fromresearch in development. Finally,we conclude with a call for researchers to take reasonable steps towards more fully incorporating culture and context into studies of development, by expanding their participant pools in strategic ways. This will lead to a more inclusive and therefore more accurate description of human development. [ABSTRACT FROM AUTHOR]

The psychological capacity to recognize that others may hold and act on false beliefs has been proposed to reflect an evolved, species-typical adaptation for social reasoning in humans; however, controversy surrounds the developmental timing and universality of this trait. Cross-cultural studies using elicited-response tasks indicate that the age at which children begin to understand false beliefs ranges from 4 to 7 years across societies, whereas studies using spontaneous-response tasks with Western children indicate that false-belief understanding emerges much earlier, consistent with the hypothesis that false-belief understanding is a psychological adaptation that is universally present in early childhood. To evaluate this hypothesis, we used three spontaneous-response tasks that have revealed early false-belief understanding in the West to test young children in three traditional, non-Western societies: Salar (China), Shuar/Colono (Ecuador) and Yasawan (Fiji). Results were comparable with those from the West, supporting the hypothesis that false-belief understanding reflects an adaptation that is universally present early in development. [ABSTRACT FROM AUTHOR]

Teaching likely evolved in humans to facilitate the faithful transmission of complex tasks. As the oldest evidenced hunting technology, spear hunting requires acquiring several complex physical and cognitive competencies. In this study, we used observational and interview data collected among BaYaka foragers (Republic of the Congo) to test the predictions that costlier teaching types would be observed at a greater frequency than less costly teaching in the domain of spear hunting and that teachers would calibrate their teaching to pupil skill level. To observe naturalistic teaching during spear hunting, we invited teacher–pupil groupings to spear hunt while wearing GoPro cameras. We analysed 68 h of footage totalling 519 teaching episodes. Most observed teaching events were costly. Direct instruction was the most frequently observed teaching type. Older pupils received less teaching and more opportunities to lead the spear hunt than their younger counterparts. Teachers did not appear to adjust their teaching to pupil experience, potentially because age was a more easily accessible heuristic for pupil skill than experience. Our study shows that costly teaching is frequently used to transmit complex tasks and that instruction may play a privileged role in the transmission of spear hunting knowledge. [ABSTRACT FROM AUTHOR]

Humans are selective social learners. In a cultural landscape with many potential models, learners must balance the cost associated with learning from successful models with learning from accessible ones. Using structured interviews, we investigate the model selection biases of Congolese BaYaka adolescent boys learning to hunt with spears (n = 24; mean age [ m age] = 15.79 years; range, 12–20 years). Results from social relations models suggest that adolescents nominated accessible adult men (closely related kin and neighbors) as preferred spear hunting models. Direct cues for success were not strong predictors for adolescent nomination in the statistical models, despite learners justifying model selection according to teaching and spear hunting skill. Indirect cues including body mass index, age, and cross-domain prestige were weak predictors for adolescent nomination. We interpret these findings as suggesting that BaYaka spear hunting knowledge is widely shared in the community, with all adult men participating in spear hunting and therefore having the requisite experience to transmit this skill. This supports previous findings that in egalitarian societies with low rates of role specialization, prestige has limited importance for cross-domain learning. [ABSTRACT FROM AUTHOR]

Giving is an act of great social importance across cultures, with communicative as well as moral dimensions because it is linked to sharing and fairness. We critically evaluate various explanations for how this social process develops in infancy and take a process-relational approach, using naturalistic observations to illustrate forms of interaction involving the exchange of objects and possible developmental trajectories for the emergence of different forms of giving. Based on our data, we propose that the object becomes a pivot point for interaction, and through the process of such interaction the social actions of showing and giving emerge and take on diverse social meanings within the relations between infants and caregivers. [ABSTRACT FROM AUTHOR]

Aspects of human life history and cognition, such as our long childhoods and extensive use of teaching, theoretically evolved to facilitate the acquisition of complex tasks. The present paper empirically examines the relationship between subsistence task difficulty and age of acquisition, rates of teaching, and rates of oblique transmission among Hadza and BaYaka foragers from Tanzania and the Republic of Congo. We further examine cross-cultural variation in how and from whom learning occurred. Learning patterns and community perceptions of task difficulty were assessed through interviews. We found no relationship between task difficulty, age of acquisition, and oblique transmission, and a weak but positive relationship between task difficulty and rates of teaching. While same-sex transmission was normative in both societies, tasks ranked as more difficult were more likely to be transmitted by men among the BaYaka, but not among the Hadza, potentially reflecting cross-cultural differences in the sexual division of subsistence and teaching labor. Further, the BaYaka were more likely to report learning via teaching, and less likely to report learning via observation, than the Hadza, possibly owing to differences in socialization practices. [ABSTRACT FROM AUTHOR]

• Pipe cleaner play did not improve BaYaka and Bondongo children's hook task success. • Children innovated novel uses for pipe cleaners outside the experimental context. • Prior relevant experience may improve children's performance during innovation tasks. • Combining observations and experiments improves our understanding of tool innovation. Tool innovation has played a crucial role in human adaptation. Yet, this capacity seems to arise late in development. Before 8 years of age, many children struggle to solve the hook task, a common measure of tool innovation that requires modification of a straight pipe cleaner into a hook to extract a prize. Whether these findings are generalizable beyond postindustrialized Western children remains unclear. In many small-scale subsistence societies, children engage in daily tool use and modification, experiences that theoretically could enhance innovative capabilities. Although two previous studies found no differences in innovative ability between children from Western and small-scale subsistence societies, these did not account for the latter's inexperience with pipe cleaners. Thus, the current study investigated how familiarity with pipe cleaners affected hook task success in 132 Congolese BaYaka foragers (57 girls) and 59 Bondongo fisher–farmers (23 girls) aged 4–12 years. We contextualized these findings within children's interview responses and naturalistic observations of how pipe cleaners were incorporated into daily activities. Counter to our expectation, prior exposure did not improve children's performance during the hook task. Bondongo children innovated significantly more hooks than BaYaka children, possibly because they participate in hook-and-line fishing. Observations and interviews showed that children imagined and innovated novel uses for pipe cleaners outside the experimental context, including headbands, bracelets, and suspenders. We relate our findings to ongoing debates regarding systematic versus unsystematic tool innovation, the importance of prior experience for the ontogeny of tool innovation, and the external validity of experimental paradigms. [ABSTRACT FROM AUTHOR]