Elsa Addessi

Specific Social Influences On the Acceptance of Novel Foods In 2–5-Year-Old Children

Social influences have been shown to be very important to overcome food neophobia in young children. However, there is no experimental evidence about whether social influences on food acceptance are specific, that is if models eating the same food as the child are more effective in promoting food acceptance than models eating a different food. We assessed childrens behavior towards novel foods when an adult model (a) was not eating (Presence condition), (b) was eating a food of a Different color (Different color condition), and (c) was eating a food of the Same color (Same color condition). We tested 27 children (ages 2- to 5-years-old) recruited from The Pennsylvania State University day-care facilities. Results show that children accepted and ate their novel food more in the Same color condition than in the Different color and in the Presence conditions. Therefore, in young children food acceptance is promoted by specific social influences. These data indicate that children are more likely to eat new food if others are eating the same type of food than when others are merely present or eating another kind of food.

The Evolution of Self-Control

Significance Although scientists have identified surprising cognitive flexibility in animals and potentially unique features of human psychology, we know less about the selective forces that favor cognitive evolution, or the proximate biological mechanisms underlying this process. We tested 36 species in two problem-solving tasks measuring self-control and evaluated the leading hypotheses regarding how and why cognition evolves. Across species, differences in absolute (not relative) brain volume best predicted performance on these tasks. Within primates, dietary breadth also predicted cognitive performance, whereas social group size did not. These results suggest that increases in absolute brain size provided the biological foundation for evolutionary increases in self-control, and implicate species differences in feeding ecology as a potential selective pressure favoring these skills. Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.

Do capuchin monkeys, Cebus apella, know what conspecifics do and do not see?

Capuchin monkeys were tested in five experiments in which two individuals competed over food. When given a choice between retrieving a piece of food that was visible or hidden from the dominant, subordinate animals preferred to retrieve hidden food. This preference is consistent with the hypotheses that either (1) the subordinate knew what the dominant could and could not see or (2) the subordinate was monitoring the behaviour of the dominant and avoiding the piece of food that it approached. To test between these alternatives, we released subordinates with a slight head start forcing them to make their choice (between a piece of food hidden or visible to the dominant) before the dominant entered the area. Unlike chimpanzees, Pan troglodytes, subordinates that were given a head start did not preferentially approach hidden pieces of food first. Therefore, our experiments provide little support for the hypothesis that capuchin monkeys are sensitive to what another individual does or does not see. We compare our results with those obtained with chimpanzees in the same paradigm and discuss the evolution of primate social cognition.

Does inequity aversion depend on a frustration effect? A test with capuchin monkeys (Cebus apella)

Brosnan and de Waal (Nature 425:297–299, 2003) reported that if a witness monkey saw a model monkey receive a high-value food, the witness was more inclined to reject a previously acceptable, but low-value food. Later work demonstrated that this alleged inequity aversion might be due to frustration induced by switching subjects from their role as models receiving a high-value food to the role of witnesses receiving a low-value food. In the present study, pairs of female capuchins exchanged a token for either a high- or a low-value food without switching their model–witness roles. Witnesses could exchange a token for a low-value food after an adjacent model had exchanged a token for the same food (Equity Condition) or for a high-value food (Inequity Condition). Failure- and latency-to-exchange measures showed that witnesses were unaffected by the food type offered to models (no inequity aversion). Moreover, models were unaffected by their history of food type offered (no frustration). These results join earlier work suggesting that alleged inequity effects depend on frustration-induction procedures. Furthermore, inequity effects sometimes fail to emerge because frustration induction in nonhuman primates is labile.

Food and token quantity discrimination in capuchin monkeys (Cebus apella)

Quantity discrimination is adaptive in a variety of ecological contexts and different taxa discriminate stimuli differing in numerousness, both in the wild and in laboratory settings. Quantity discrimination between object arrays has been suggested to be more demanding than between food arrays but, to our knowledge, the same paradigm has never been used to directly compare them. We investigated to what extent capuchin monkeys’ relative numerousness judgments (RNJs) with food and token are alike. Tokens are inherently non-valuable objects that acquire an associative value upon exchange with the experimenter. Our aims were (1) to assess capuchins’ RNJs with food (Experiment 1) and with tokens (Experiment 2) by presenting all the possible pair-wise choices between one to five items, and (2) to evaluate on which of the two proposed non-verbal mechanisms underlying quantity discrimination (analogue magnitude and object file system) capuchins relied upon. In both conditions capuchins reliably selected the larger amount of items, although their performance was higher with food than with tokens. The influence of the ratio between arrays on performance indicates that capuchins relied on the same system for numerical representation, namely analogue magnitude, regardless of the type of stimuli (food or tokens) and across both the small and large number ranges.

Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance

Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.

Social facilitation of eating novel food in tufted capuchin monkeys (Cebus apella): input provided by group members and responses affected in the observer.

Abstract. Learning about food palatability from watching what conspecifics eat might be one of the advantages of group living. A previous study investigated whether group members’ presence or eating activity account for social facilitation of eating of foods never previously tasted. Capuchins encountered novel colored foods when (1) alone (Alone condition) or (2) with group members visible in the nearby cage (Group-present condition) or (3) with group members present and eating a familiar food that had not been colored (Group+food condition). Social facilitation of eating occurred when group members were eating, despite the difference in color between the familiar food eaten by them and the novel food presented to the experimental subject. To clarify what subjects learnt from group members when social facilitation occurred, we further analyze here the data from the previous study. The number of visual exposures to the colored novel food (as a group member) correlated with increased consumption of that novel food when encountered later (as experimental subject). In contrast, the number of times that an individual fed on the familiar food (as a group member) did not decrease its consumption of novel food (as experimental subject). Therefore, capuchins (1) habituated to the colors of the novel foods, and (2) did not take into account that seeing group members eating a food does not provide information about the palatability of a differently colored food. Since social facilitation of eating occurs when foods do not match in color, at least in capuchins, social facilitation of eating should not be considered as a way of learning about a safe diet, but rather as a way of overcoming neophobia.

Delay Choice Versus Delay Maintenance: Different Measures of Delayed Gratification in Capuchin Monkeys (Cebus apella)

Delaying gratification involves 2 components: (1) delay choice (selecting a delayed reward over an immediate one) and (2) delay maintenance (sustaining the decision to delay gratification even if the immediate reward is available during the delay). Two tasks most commonly have explored these components in primates: the intertemporal choice task and the accumulation task. It is unclear whether these tasks provide equivalent measures of delay of gratification. Here, we compared the performance on the intertemporal choice task and the accumulation task of capuchin monkeys (Cebus apella) belonging to 2 study populations. We found only limited evidence of a significant correlation in performance. Consequently, in contrast to what is often assumed, our data provide only partial support for the hypothesis that these tasks provide equivalent measures of delay of gratification.

Social Facilitation of Eating Familiar Food in Tufted Capuchins (Cebus apella): Does it Involve Behavioral Coordination?

Social facilitation of eating familiar foods might serve to synchronize eating activities within groups. We aimed to assess whether capuchins (Cebus apella) are prompted to eat when observing other conspecifics eating a familiar food. Subjects were 8 male captive-born tufted capuchins. One pair of capuchins acted as demonstrators for the other 6 observer subjects. In the Experimental condition, the demonstrator pair was given fresh chow in addition to having access to the leftover food and ate continuously. In the Control condition, the demonstrator pair had access to food leftover from the morning feed and ate very little. The initiation of feeding by the demonstrator pair prompted the initiation of feeding behavior in the observers, and the latter ate significantly more of their leftovers in the Experimental than in the Control condition. The tempo ofthe social facilitation of eating familiar foods in capuchins supportisomorphic coordination, a process that occurs when one individual’s activity focuses the attention of another individual to the same activity, thereby increasing behavioral similarity in a group.

Preferences towards novel foods in Cebus apella: the role of nutrients and social influences

Information on the process of preference acquisition towards novel foods in nonhuman primates is lacking. This study aims to assess (1) whether nutrient and energy contents affect preferences towards novel foods encountered repeatedly by individuals when alone, (2) whether these preferences change after additional encounters with the novel foods, and (3) if the change is sensitive to social influences. We presented seven novel foods to 26 socially housed tufted capuchins. In Phase 1, each subject was presented individually with the 21 possible binary combinations of the seven novel foods. Afterwards, during treatment, 13 subjects received the novel foods ad libitum with their group members (social condition) and 13 subjects received the foods individually (individual condition); subjects assigned to the individual and social conditions had shown similar food preferences in Phase 1. Finally, in Phase 2, each subject was presented again with 21 binary choices between each of the novel foods. In Phases 1 and 2, the number of times each food was chosen differed among foods. In Phase 1, food preference correlated positively with glucose and fructose and negatively with total fiber content. In Phase 2, irrespective of social or individual prior experience in the treatment condition, food preference changed and became correlated with total energy content. Our results broaden the findings already available for familiar foods by demonstrating that individual experience based on the feedback obtained from novel foods guides the establishment of preferences towards them. Moreover, individual experience is sufficient to determine food preferences similar to those individuals may acquire when together with group members eating the same foods.