Available and unavailable decoys in capuchin monkeys (Sapajus spp.) decision-making.

Decision-making has been observed to be systematically affected by decoys, i.e., options that should be irrelevant, either because unavailable or because manifestly inferior to other alternatives, and yet shift preferences towards their target. Decoy effects have been extensively studied both in humans and in several other species; however, evidence in non-human primates remains scant and inconclusive. To address this gap, this study investigates how choices in capuchin monkeys (Sapajus spp.) are affected by different types of decoys: asymmetrically dominated decoys, i.e., available and unavailable options that are inferior to only one of the other alternatives, and phantom decoys, i.e., unavailable options that are superior to another available alternative. After controlling for the subjective strength of initial preferences and the distance of each decoy from its target in attribute space, results demonstrate a systematic shift in capuchins' preference towards the target of both asymmetrically dominated decoys (whether they are available or not) and phantom decoys, regardless of what options is being targeted by such decoys. This provides the most comprehensive evidence to date of decoy effects in non-human primates, with important theoretical and methodological implications for future comparative studies on context effects in decision-making.

Complementary feeding approach and maternal responsiveness in 8- and 12-month-old Italian infants: A longitudinal study.

In Western countries, infants are usually introduced to solids through spoon-fed puréed foods (parent-led weaning, PLW). However, an alternative approach known as "baby-led weaning" (BLW), in which infants usually participate in family meals and eat independently, is becoming increasingly popular. We investigated the relationship between the type of complementary feeding approach and maternal responsiveness to infant feeding cues in a longitudinal sample of 178 infants observed at 8 and 12 months. Mothers reported the complementary feeding method used and, from video-recorded meals, we coded the proportion of time infants self-fed and rated maternal responsiveness by means of the Responsiveness to Child Feeding Cues Scale (Hodges et al., 2013). Responsiveness to infant receptiveness and fullness cues were significantly correlated at 8 months, but not at 12 months, when unresponsiveness decreased for receptiveness but remained stable for fullness cues. Thus, as infants got older, mothers were increasingly tuned in to their receptiveness cues. However, we did not observe the same pattern for fullness cues, perhaps because mothers were concerned that their infants did not eat enough. Moreover, at both time points, mothers were more responsive to infants' receptiveness than fullness cues, possibly due to an evolutionary drive to protect infants from starvation. Finally, responsiveness to fullness, but not responsiveness to receptiveness, was positively related to the proportion of infant self-feeding, but there were no significant differences in responsiveness depending on the self-reported complementary feeding approach. Thus, a weaning style that emphasizes independent feeding, regardless of whether this is labeled as BLW, may promote more infant-centered maternal responses at the end of the meal, with potential implications for promoting infant self-regulation not only at mealtimes, but also in other domains.

State-dependent risky choices in primates: Variation in energy budget does not affect tufted capuchin monkeys' (Sapajus spp.) risky choices.

Economic models predict that rational decision makers' choices between a constant, "safe" option and a variable, "risky" option leading, on average, to the same payoff, should be random. However, a wealth of research has revealed that, when faced with risky decisions, both human and nonhuman animals deviate from economic rationality. According to the risk-sensitivity theory, individuals should prefer a safe option when they are in a positive energy state and a risky option when they are in a negative energy state. The abundance/risk hypothesis proposes that individuals should prefer risky options when diet quality exceeds their nutritional requirements. We tested how energy budget affects decision making under risk by presenting 22 capuchins belonging to two colonies (IT: N = 12, US: N = 10) with a risky choice task. Capuchins had to choose between a constant option (always four food items) and a variable option (one or seven food items with a 50% probability) in two conditions. In the Low-energy condition capuchins were tested before their main meal, whereas in the High-energy condition they were tested following a high-caloric meal. In neither colony did we find a significant difference between conditions, suggesting that the energy budget did not affect risk preferences. However, we found differences between colonies in their general response to risky choices: US capuchins were more risk-prone after selecting a safe option than a risky option and after selecting a bad (one food item) than a good (seven food items) risky option, whereas this did not hold true in IT capuchins. Furthermore, in the IT colony, males were more risk-prone under the High-energy condition compared to the Low-energy condition. Subtle differences in individual characteristics, management conditions, or stochastic founder effects may be implied, with relevant consequences for the outcomes of research on risky decision-making across laboratories.

Context-effect bias in capuchin monkeys (Sapajus spp.): exploring decoy influences in a value-based food choice task.

Decision making is known to be liable to several context effects. In particular, adding a seemingly irrelevant alternative (decoy) to a set of options can modify preferences: typically, by increasing choices towards whatever option clearly dominates the decoy (attraction effect), but occasionally also decreasing its appeal and generating a shift in the opposite direction (repulsion effect). Both types of decoy effects violate rational choice theory axioms and suggest dynamic processes of preference-formation, in which the value of each alternative is not determined a priori, but it is instead constructed by comparing options during the decision process. These effects are well documented, both in humans and in other species: e.g., amoebas, ants, honeybees, frogs, birds, cats, dogs. However, evidence of decoy effects in non-human primates remains surprisingly mixed. This study investigates decoy effects in capuchin monkeys (Sapajus spp.), manipulating time pressure across different conditions, to test whether such effects require time-consuming comparative processes among available alternatives. Whereas the time-dependent nature of decoy effects is a robust finding in the human literature, this is its first investigation in non-human animals. Our results show that capuchins exhibit an attraction effect with decoys targeting their preferred food, and that this effect disappears under time pressure; moreover, we observe preliminary evidence of a repulsion effect when decoys target instead the less-preferred food, possibly due to the larger distance between decoy and target in the attribute space. Taken together, these results provide valuable insight on the evolutionary roots of comparative decision making.

Infant sleep and development: Concurrent and longitudinal relations during the first 8 months of life.

Sleep is an essential function of human life, underlying both biological and cultural processes. Dramatic changes in sleep occur during infancy, in terms of night awakenings, which tend to diminish over time, and day/night sleep duration, with newborns sleeping up to 16-17 h per day and gradually decreasing to 9-13 h between 6 and 11 months of age. Remarkably, research indicates that changes in infant sleep are in interaction with important acquisitions in other domains of child development. In the present study, we aimed at investigating concurrent and longitudinal relations between sleep and cognitive maturation during infancy, by collecting data on 156 infants at 4 and 8 months of age. Infants' sleep was assessed through the Brief Infant Sleep Questionnaire (BISQ; Sadeh, 2004), whereas cognitive maturation was evaluated using the Developmental Profile™ 3 (Alpern 2007). We also examined infants' language understanding through the short form of the Italian version of the MacArthur-Bates Communicative Development Inventory (MCDI-SF): Words and Gestures (Caselli, Bello, Rinaldi, Stefanini, & Pasqualetti, 2015; Fenson et al., 2000). Finally, information about infants' temperament and maternal practices potentially relevant for sleep quality, such as the use of a pacifier at nighttime, co-sleeping and exclusive breastfeeding, was detected. Results showed that night and day sleep were differently related to infants' development at 4 and 8 months of age, but there were no robust longitudinal relationships.

Online Assessment of Motor, Cognitive, and Communicative Achievements in 4-Month-Old Infants.

Remote methods for data collection allow us to quickly collect large amounts of data, offering several advantages as compared to in-lab administration. We investigated the applicability of an online assessment of motor, cognitive, and communicative development in 4-month-old infants based on several items of the Bayley Scales of Infant Development, 3rd edition (BSID-III). We chose a subset of items which were representative of the typical developmental achievements at 4 months of age and that we could administer online with the help of the infant's caregiver using materials which were easily available at home. Results showed that, in a sample of infants tested live (N = 18), the raw scores of the BSID-III were significantly correlated with the raw scores of a subset of items corresponding to those administered to a sample of infants tested online (N = 53). Moreover, for the "online" participants, the raw scores of the online assessment did not significantly differ from the corresponding scores of the "live" participants. These findings suggest that the online assessment was to some extent comparable to the live administration of the same items, thus representing a viable opportunity to remotely evaluate infant development when in-person assessment is not possible.

The presence of a potential competitor modulates risk preferences in rats.

Although both human and non-human animals, in everyday life, deal with risky decisions in a social environment, few studies investigated how social dimension influences risk preferences (i.e., if consequences on others feeds back over own choice). Here, we assessed whether the presence of a conspecific, acting as a potential competitor for the same food resource, influenced risky decision-making in male rats. Subjects received a series of choices between a safe option (always yielding a small yet optimal reward, solely to itself) and a risky option (yielding a larger but suboptimal reward, one third of times to itself and two third of times delivered to the other half cage); rats were tested twice, both alone and paired with a conspecific, recipient of own-lost food and hence acting as potential competitor. Results showed that focal subjects were more risk-prone when paired with a conspecific than when tested alone. However, rats exhibited also a higher motivational conflict with a competing bystander present than alone: data suggest that the primary drive was to increase "own" food rather than either a competitive or prosocial tendency. Overall, for rats tested in a risky-choice task, a competitive social context increased the salience and attractiveness of larger food outcomes, as observed in humans and great apes. This led to the economically irrational response of selecting the "binge-but-risky" option, notwithstanding uncertainty about the actual recipient of such food.

Searching for a Relationship between Early Breastfeeding and Cognitive Development of Attention and Working Memory Capacity.

Previous research consistently reported that subjects that were exclusively breastfed (eBF) vs. not-exclusively breastfed (neBF) during infancy (0-6 months) showed increased scores of general intelligence measures (e.g., the intelligence quotient). However, the existent literature largely neglected whether breastfeeding also affects specific cognitive processes, such as attention and working memory (WM) capacity. We tested whether eBF vs. neBF subjects showed performance differences in relation to these two core cognitive functions. The Attention Network Test (ANT), to measure alerting, orienting, and conflict, and the Change Colour Task (CCT), to measure visuospatial WM capacity, were administered to 144 participants divided according to age (6-, 10-, and 18-year-old participants) and breastfeeding (eBF or neBF during 0-6 months of life). Importantly, the sub-groups were homogenous in terms of maternal education, a factor potentially affecting the relation between breastfeeding and cognition. While we found increased performance as a function of participants' age in both tasks, we failed to observe effects related to breastfeeding, as evidenced by Bayesian analyses. These findings highlight for the first time that the pattern of nutrition provided during early infancy does not appear to affect the development of attention and WM capacity, at least starting from the age considered in the present study.

Baby-led weaning in Italy and potential implications for infant development.

Baby-led weaning is an approach to complementary feeding that emphasizes an infant's ability to self-feed rather than being spoon fed, and to eat minimally-processed foods rather than puréed foods. This study aimed to investigate the variability in infant feeding practices and the possible association with developmental milestones in an Italian population. A sample of 1245 mothers of 6-12 month-old infants completed an online survey about complementary feeding and their infant's attainment of developmental milestones. Infants' eating of family food was positively related to self-feeding and to a lower consumption of puréed foods. As in previous studies in the UK and New Zealand, a baby-led weaning style was positively associated with breastfeeding, exposure to complementary foods around six months of age, earlier exposure to both finger and family foods, and higher interest in family food and shared family meals. Infants who were introduced to solid foods using a baby-led weaning approach were more likely to have met important developmental milestones; when controlling for covariates, percentage of family feeding was positively associated with sitting unsupported at an earlier age and a low spoon-feeding style was associated with crawling at an earlier age. These data suggest that baby-led weaning should be defined more comprehensively. Moreover, its potential influence on developmental domains beyond diet and eating behavior warrants future targeted exploration.

An infant-led approach to complementary feeding is positively associated with language development.

The timing and strategy with which parents first introduce their infants to solid foods may be an important predictor of subsequent developmental outcomes. Recent years have seen a decline in the prevalence of traditional parent-led feeding of soft, puréed food and a rise in the prevalence of infant-led complementary feeding. Although there has been some research espousing the benefits of infant-led complementary feeding for improving food fussiness and self-regulation, there has been little exploration of this approach that may impact on other developmental outcomes in children. The current study explores whether aspects of the infant-led approach, specifically the child eating unaided and consuming finger foods and eating with the family, are related to child language outcomes. One hundred thirty one parents of children aged 8-24 months completed questionnaires about their approach to complementary feeding, their current feeding practices, their child's experiences with family foods and child language comprehension/production. The findings suggest that an approach to complementary feeding which promotes infant autonomy in feeding (i.e., eating finger foods rather than puréed foods) and consuming more family foods is related to more advanced child language production and comprehension. Specifically, the prevalence of eating family foods mediated the relationship between eating unaided at the onset of the complementary feeding period and later language outcomes. This study is the first to find a significant relationship between different approaches to introducing solid foods and child language outcomes and these findings highlight the potential for different complementary feeding approaches to influence behaviour beyond mealtimes.

Economic behaviours among non-human primates.

Do we have any valid reasons to affirm that non-human primates display economic behaviour in a sufficiently rich and precise sense of the phrase? To address this question, we have to develop a set of criteria to assess the vast array of experimental studies and field observations on individual cognitive and behavioural competences as well as the collective organization of non-human primates. We review a sample of these studies and assess how they answer to the following four main challenges. (i) Do we see any economic organization or institutions emerge among groups of non-human primates? (ii) Are the cognitive abilities, and often biases, that have been evidenced as underlying typical economic decision-making among humans, also present among non-human primates? (iii) Can we draw positive lessons from performance comparisons among primate species, humans and non-humans but also across non-human primate species, as elicited by canonical game-theoretical experimental paradigms, especially as far as economic cooperation and coordination are concerned? And (iv) in which way should we improve models and paradigms to obtain more ecological data and conclusions? Articles discussed in this paper most often bring about positive answers and promising perspectives to support the existence and prevalence of economic behaviours among non-human primates. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

Are capuchin monkeys (Sapajus spp.) sensitive to lost opportunities? The role of opportunity costs in intertemporal choice.

Principles of economics predict that the costs associated with obtaining rewards can influence choice. When individuals face choices between a smaller, immediate option and a larger, later option, they often experience opportunity costs associated with waiting for delayed rewards because they must forego the opportunity to make other choices. We evaluated how reducing opportunity costs affects delay tolerance in capuchin monkeys. After choosing the larger option, in the High cost condition, subjects had to wait for the delay to expire, whereas in the Low cost different and Low cost same conditions, they could perform a new choice during the delay. To control for the effect of intake rate on choices, the Low cost same condition had the same intake rate ratio as the High cost condition. We found that capuchins attended both to intake rates and to opportunity costs. They chose the larger option more often in the Low cost different and Low cost same conditions than in the High cost condition, and more often in the Low cost different condition than in the Low cost same condition. Understanding how non-human primates represent and use costs in making decisions not only helps to develop theoretical frameworks to explain their choices but also addresses similarities with and differences from human decision-making. These outcomes provide insights into the origins of human economic behaviour. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

Testing the two sides of indirect reciprocity in tufted capuchin monkeys.

We addressed two different aspects of indirect reciprocity in tufted capuchin monkeys (Sapajus spp.) studying two common cooperative behaviours, grooming and food sharing. In an observational study, we tested whether capuchin monkeys were more likely to groom an individual that had just groomed a group mate than an individual that had not groomed anybody. In an experimental study, we tested whether capuchin monkeys were more likely to share their food with a partner when in the presence of a bystander (or of an image of the eyes of a conspecific) than when alone with their partner. In the observational study, we found an increase in the likelihood of receiving grooming after giving grooming, but this effect seemed to depend on social facilitation rather than on indirect reciprocity, as we found a similar effect after receiving (rather than giving) grooming. In the experimental study, the presence of a bystander or of an image of eyes did not affect the amount of food transferred to a group mate. Overall, these results suggest capuchin monkeys do not engage in indirect reciprocity.

Contextual factors modulate risk preferences in adult humans.

Humans have generally been considered risk averse for gains. Yet, growing evidence shows that risk preferences may change across reward currencies and depend on the type of tasks used to measure them. Here, we examined how context affects human risk preferences to shed light on the psychological mechanisms underlying human decision-making under risk. Participants were presented with a descriptive risky choice task involving repeated choices between real options and they were provided with trial-by-trial feedback. We manipulated the type of reward and, for the first time, the format of the choice stimuli. Options were either 2D computer-based images or concrete 3D objects, and participants received food or money as reward. First, we found that participants were more risk-seeking for food compared to money, suggesting that people treat money differently from consumable rewards. Second, we found that people were more risk-seeking when they made choices between concrete 3D objects than between 2D computer-based images. Our results strengthened the evidence that human choice patterns may change depending on the context and, for the first time, showed that the format of the choice stimuli does affect risk preferences, an important consideration for future research.

Are the roots of human economic systems shared with non-human primates?

We review and analyze evidence for an evolutionary rooting of human economic behaviors and organization in non-human primates. Rather than focusing on the direct application of economic models that a priori account for animal decision behavior, we adopt an inductive definition of economic behavior in terms of the contribution of individual cognitive capacities to the provision of resources within an exchange structure. We spell out to what extent non-human primates' individual and strategic decision behaviors are shared with humans. We focus on the ability to trade, through barter or token-mediated exchanges, as a landmark of an economic system among members of the same species. It is an open question why only humans have reached a high level of economic sophistication. While primates have many of the necessary cognitive abilities (symbolic and computational) in isolation, one plausible issue we identify is the limits in exerting cognitive control to combine several sources of information. The difference between human and non-human primates' economies might well then be in degree rather than kind.

Evolutionary origins of money categorization and exchange: an experimental investigation in tufted capuchin monkeys (Sapajus spp.).

Money is a cultural artefact with a central role in human society. Here, we investigated whether some features of money may be traced back to the exchange habits of nonhuman animals, capitalizing on their ability to flexibly use tokens in different domains. In Experiment 1, we evaluated whether capuchins can recognize token validity. Six subjects were required to exchange with the experimenter valid/familiar tokens, valid/unfamiliar tokens, invalid tokens, and no-value items. They first exchanged a similar number of valid/familiar and valid/unfamiliar tokens, followed by exchanges of invalid tokens and no-value items. Thus, as humans, capuchins readily recognized token validity, regardless of familiarity. In Experiment 2, we further evaluated the flexibility of the token-food association by assessing whether capuchins could engage in reverse food-token exchanges. Subjects spontaneously performed chains of exchanges, in which a food item was exchanged for a token, and then the token was exchanged for another food. However, performance was better as the advantage gained from the exchange increased. Overall, capuchins recognized token validity and successfully engaged in chains of reverse and direct exchanges. This suggests that-although nonhuman animals are far from having fully-fledged monetary systems-for capuchins tokens share at least some features with human money.

Polymorphism of the 3'-UTR of the dopamine transporter gene (DAT) in New World monkeys.

Genetic polymorphism in the 3'-untranslated region (3'-UTR) of the dopamine transporter (DAT) gene has been reported in both human and nonhuman primates, and the variable number of tandem repeats (VNTR) polymorphism has been related to several neurological and psychiatric disorders. As New World primates have been employed as models in biomedical research in these fields, in the present study we assessed genetic variation in the DAT gene in 25 robust capuchin monkeys (Sapajus spp.) and 39 common marmosets (Callithrix jacchus). Using enzymatic amplification followed by sequencing of amplified fragments, a VNTR polymorphism in the 3'-UTR region of the DAT gene was identified in both robust capuchins and common marmosets. The polymorphic tandem repeat of 40-bp basic units is similar to the human VNTR consensus sequence, with size variants composed of 9, 10, and 11 units in marmosets and 8, 9, 13, and 17 basic units in capuchins. We found behavioral evidence that carrying the 10-repeat DAT allele promotes flexible choice and maximization of foraging in marmosets tested in an operant choice paradigm. Moreover, in an intertemporal choice task, capuchins with longer repeat variants show less self-controlled choices than capuchins with at least one short repeat variant. Future research should focus on the relationship between these DAT polymorphisms, dopamine reuptake via the dopamine transporter, and behavioral and cognitive variation across New World monkey individuals.

Self-control depletion in tufted capuchin monkeys (Sapajus spp.): does delay of gratification rely on a limited resource?

Self-control failure has enormous personal and societal consequences. One of the most debated models explaining why self-control breaks down is the Strength Model, according to which self-control depends on a limited resource. Either previous acts of self-control or taking part in highly demanding cognitive tasks have been shown to reduce self-control, possibly due to a reduction in blood glucose levels. However, several studies yielded negative findings, and recent meta-analyses questioned the robustness of the depletion effect in humans. We investigated, for the first time, whether the Strength Model applies to a non-human primate species, the tufted capuchin monkey. We tested five capuchins in a self-control task (the Accumulation task) in which food items were accumulated within individual's reach for as long as the subject refrained from taking them. We evaluated whether capuchins' performance decreases: (i) when tested before receiving their daily meal rather than after consuming it (Energy Depletion Experiment), and (ii) after being tested in two tasks with different levels of cognitive complexity (Cognitive Depletion Experiment). We also tested, in both experiments, how implementing self-control in each trial of the Accumulation task affected this capacity within each session and/or across consecutive sessions. Repeated acts of self-control in each trial of the Accumulation task progressively reduced this capacity within each session, as predicted by the Strength Model. However, neither experiencing a reduction in energy level nor taking part in a highly demanding cognitive task decreased performance in the subsequent Accumulation task. Thus, whereas capuchins seem to be vulnerable to within-session depletion effects, to other extents our findings are in line with the growing body of studies that failed to find a depletion effect in humans. Methodological issues potentially affecting the lack of depletion effects in capuchins are discussed.

False belief understanding and "cool" inhibitory control in 3-and 4-years-old Italian children.

During preschool years, major developments occur in both executive function and theory of mind (ToM), and several studies have demonstrated a correlation between these processes. Research on the development of inhibitory control (IC) has distinguished between more cognitive, "cool" aspects of self-control, measured by conflict tasks, that require inhibiting an habitual response to generate an arbitrary one, and "hot," affective aspects, such as affective decision making, measured by delay tasks, that require inhibition of a prepotent response. The aim of this study was to investigate the relations between 3- and 4-year-olds' performance on a task measuring false belief understanding, the most widely used index of ToM in preschoolers, and three tasks measuring cognitive versus affective aspects of IC. To this end, we tested 101 Italian preschool children in four tasks: (a) the Unexpected Content False Belief task, (b) the Conflict task (a simplified version of the Day-Night Stroop task), (c) the Delay task, and (d) the Delay Choice task. Children's receptive vocabulary was assessed by the Peabody Picture Vocabulary test. Children's performance in the False Belief task was significantly related only to performance in the Conflict task, controlling for vocabulary and age. Importantly, children's performance in the Conflict task did not significantly correlate with their performance in the Delay task or in the Delay Choice task, suggesting that these tasks measure different components of IC. The dissociation between the Conflict and the Delay tasks may indicate that monitoring and regulating a cool process (as flexible categorization) may involve different abilities than monitoring and regulating a hot process (not touching an available and highly attractive stimulus or choosing between a smaller immediate option and a larger delayed one). Moreover, our findings support the view that "cool" aspects of IC and ToM are interrelated, extending to an Italian sample of children previous findings on an association between self-control and ToM.