Comparing apples to manzanas and oranges to naranjas: A new measure of English-Spanish vocabulary for dual language learners.

The valid assessment of vocabulary development in dual-language-learning infants is critical to developmental science. We developed the Dual Language Learners English-Spanish (DLL-ES) Inventories to measure vocabularies of U.S. English-Spanish DLLs. The inventories provide translation equivalents for all Spanish and English items on Communicative Development Inventory (CDI) short forms; extended inventories based on CDI long forms; and Spanish language-variety options. Item-Response Theory analyses applied to Wordbank and Web-CDI data (n = 2603, 12-18 months; n = 6722, 16-36 months; half female; 1% Asian, 3% Black, 2% Hispanic, 30% White, 64% unknown) showed near-perfect associations between DLL-ES and CDI long-form scores. Interviews with 10 Hispanic mothers of 18- to 24-month-olds (2 White, 1 Black, 7 multi-racial; 6 female) provide a proof of concept for the value of the DLL-ES for assessing the vocabularies of DLLs.

Different patterns of sensitivity differentially affect infant attention span.

We exposed infants to different types of sensitive behavior to examine effects on infants' attention. Results revealed infants changed their patterns of visual attention; infants had longer durations of sustained attention to toys, shorter durations to the social partner, and fewer attention shifts when interacting with a nonvocal social partner than when interacting with a vocal social partner.

From 'ah' to 'bah': social feedback loops for speech sounds at key points of developmental transition.

Social feedback is a driving force for speech development. A recent study provided a key finding to explain how contingent responses influence developmental change: infant speech-related vocalizations are contingent on responses to prior speech-related vocalizations (Warlaumont et al., 2014). However, the study did not distinguish between different speech-related vocalizations, vowel-like (V) and consonant-vowel (CV) vocalizations, which is important because CV vocalizations are a precursor to words. The present study explored parents' responses to infants' vocalizations and infants' subsequent vocal production at a point when vocalizations become more like adult speech. The relative proportion of CVs following contingent responses to CV did not differ between 10- and 12-months-olds; however, there was only a significant contingent relationship between responses to CV and subsequent CV production in 12-month-olds. Results suggest a developmental transition and a social feedback loop for the production of more developmentally advanced sounds when infants are learning their first words.

Motivation Counts: Autonomous But Not Obligated Sharing Promotes Happiness in Preschoolers.

Research has demonstrated that prosocial sharing is emotionally rewarding, which leads to further prosocial actions; such a positive feedback loop suggests a proximal mechanism of human's tendency to act prosocially. However, it leaves open a question as to how the emotional benefits from sharing develop in young children and whether sharing under pressure promotes happiness as well. The current study directly compared 3- and 5-year-old Chinese children's happiness when sharing was autonomous (the recipient did not contribute to getting the reward) with when sharing was obligated (the recipient and the actor jointly earned the reward). We found that children shared more items overall when sharing was obligated than autonomous, demonstrating their conformity to social norms of merit-based sharing. In children who eventually shared with others, 5-year-olds gave out more stickers in the obligated sharing condition than in the autonomous sharing condition, but 3-year-olds shared the same amount between the conditions, suggesting that 5-year-olds adhered to the merit-based sharing norm more strictly than 3-year-olds. Moreover, in the autonomous sharing condition, children displayed greater happiness when they shared with the recipient than when they kept stickers for themselves, suggesting that costly prosocial giving benefited children with positive mood; however, children did not gain happiness when they shared with the recipient in the obligated sharing condition. These findings demonstrate that children's affective benefits depend on the motivation underlying their prosocial behavior, and further imply that normative force and emotional gains may independently drive preschoolers' prosocial behaviors.

The Effect of Social Responsiveness on Infants' Object-Directed Imitation.

Previous research has demonstrated that social interactions underlie the development of object-directed imitation. For example, infants differentially learn object action sequences from a live social partner compared to a social partner over a video monitor; however, what is not well understood is what aspects of social interactions influence social learning. Previous studies have found variable influences of different types of caregiver responsiveness on attention, language, and cognitive development. Therefore, the purpose of this study was to examine how the responsive style of a social partner influenced the learning of object-directed action sequences. Infants interacted with either a sensitive or redirective experimenter before the learning trial. Results revealed infants changed their patterns of engagement; infants interacting with a sensitive experimenter had longer periods of attentional engagement than infants interacting with a redirective experimenter. Furthermore, during the learning trial, the amount of sensitivity during interaction with the social partner predicted learning scores. These findings suggest that infants' attention is influenced by social partners' interactive style during ongoing interaction, which subsequently affects how infants learn from these social partners.

Caregivers provide more labeling responses to infants' pointing than to infants' object-directed vocalizations.

Existing studies have observed a robust relationship between infants' pointing gestures and language outcomes. By contrast, infants' overall vocal production is not related to language outcomes. One possible explanation for the association between pointing and language is that pointing gestures, as compared to vocalizations, may elicit more verbal responses from social partners that are facilitative for language learning. To test this, we observed forty-seven infants aged 1;0 during free play with their mothers and fathers separately to compare parents' verbal responses to infants' pointing gestures and object-directed vocalizations. Results showed that, compared to object-directed vocalizations, infants' pointing elicited more verbal responses from parents, particularly object labels. Moreover, mothers were more likely than fathers to provide labels. These results may help explain why pointing is associated with indices of language acquisition, but the production of vocalizations is not.

Socially guided attention influences infants' communicative behavior.

For effective prelinguistic communication, infants must be able to direct their attention, vocalizations, and nonverbal gestures in social interactions. The purpose of our study was to examine how different styles of caregiver responses influenced infant attentional and communicative behavior in social interactions, based on prior studies that have shown influences of responsiveness on attention, language and cognitive outcomes. Infants were exposed to redirective and sensitive behavior systematically using an ABA design to examine real-time changes in infants' behavior as a function of caregiver responses. During the two baseline "A" periods, caregivers were instructed to play as they would at home. During the social response "B" period, caregivers were instructed to respond sensitively to infants' behavior on one visit and redirectively on the other visit. Results demonstrated that when caregivers behaved redirectively, infants shifted their attention more frequently and decreased the duration of their visual attention. Caregiver responses also resulted in changes in vocal and gesture production. Infants decreased their production of caregiver-directed vocalizations, gestures, and gesture-vocal combinations during in the redirective condition. Results suggest that caregiver sensitive responding to infants' attentional focus may be one influence on infants' attentional and prelinguistic communicative behavior.

Male dominance and reproductive success in wild white-faced capuchins (Cebus capucinus) at Lomas Barbudal, Costa Rica.

Theory and a growing body of empirical evidence suggest that higher ranking males experience reproductive advantages in group-living mammals. White-faced capuchins (Cebus capucinus) exhibit an interesting social system for investigating the relationship between dominance and reproductive success (RS) because they live in multimale multifemale social groups, in which the alpha males can have extraordinarily long tenures (i.e. they coreside with daughters of reproductive age). Genetic paternity was determined from fecal samples for 120 infants born into three social groups of wild C. capucinus at Lomas Barbudal Biological Reserve, Costa Rica. Alpha males produced far more offspring than expected by chance, and significantly high Nonac's B indices (a measure of deviation from a random distribution of RS among potentially breeding individuals) were a feature of six out of eight male tenures. The likelihood of the alpha male siring a particular offspring was predicted by the kin relationship between the mother and the alpha male, as well as the total number of males and females in the group. The almost complete lack of father-daughter inbreeding [Muniz et al., 2006] constitutes an impediment to alpha male reproductive monopolization in this population, particularly toward the end of long alpha male tenures.

Constructing culture in cowbirds (Molothrus ater).

In past work, the authors produced divergent patterns of courtship and communication in juvenile male cowbirds (Molothrus ater) by providing them with different social experiences during their 1st year. Here the authors determined whether these different social patterns could be transmitted to new generations of juvenile males. In Experiment 1, the authors exposed groups of juveniles to adult males who differed in the amount of male-male competition they produced. In Experiment 2, they gave groups of juveniles either social access to adult males or only visual and acoustic access to those males. In both experiments, juvenile males developed patterns of courtship and competition similar to those expressed by the adult males with whom they had social contact. The juveniles never had the opportunity to observe some of the adults' behaviors that they came to replicate. This suggests that the role of the adults was to establish the social structure in the groups, modifying juveniles' early social interactions. Juveniles were then "cultured" within these different learning environments, constructing social behavior similar to the adult males' behavior in their 1st year.

Responses of white-faced capuchins (Cebus capucinus) to naturalistic and experimentally presented food-associated calls.

In the context of foraging, many animal species produce specific calls that attract others. Researchers hypothesize that these vocalizations function to inform others about food; however, few studies have investigated whether food-associated calls alone are sufficient to cause individuals to respond as if they have been informed about food. Playback experiments on white-faced capuchins (Cebus capucinus) investigated whether listeners could infer the presence of food merely by hearing food-associated calls. Recipients looked significantly longer toward the call source and approached the speaker more often after hearing food-associated calls, as compared with control calls. Because these responses are not indicative of feeding, it is unclear whether listeners associated the calls with food. Nonetheless, these responses, specific to food-associated calls, may increase individuals' chances of finding food.

Violent coalitionary attacks and intraspecific killing in wild white-faced capuchin monkeys ( Cebus capucinus).

During 12 years of observation, we have observed three confirmed and two inferred lethal coalitionary attacks on adult male white-faced capuchins ( Cebus capucinus) by members of two habituated social groups at Lomas Barbudal Biological Reserve, Costa Rica. In one case, an alpha male was badly wounded and evicted from his group, and when later found by his former groupmates he was attacked by several of them and died less than 24 h later. In two other cases, lone extra-group males were mobbed by adult and immature males of a bisexual group. One victim's abdomen was torn open and he died less than 24 h later. A second victim was quite badly bitten but may have escaped. The fourth and fifth cases resulted from intergroup encounters. One victim lost the use of both arms but may have survived, whereas the other died of unknown causes within an hour of the attack. The observed death rate from coalitionary aggression at our site is approximately the same as that reported for eastern chimpanzees. Because at least three of the five observed incidents involved large coalitions attacking lone victims, they support the general hypothesis that imbalances of power contribute to intraspecific killing in primates. However, the occurrence of lethal coalitional attacks in a species lacking fission-fusion social organization poses a challenge to the more specific version of the imbalance-of-power hypothesis proposed by Manson and Wrangham in 1991 to explain chimpanzee and human intergroup aggression.

Contexts and behavioral correlates of trill vocalizations in wild white-faced capuchin monkeys (Cebus capucinus).

Primate vocalizations that appear to occur independently of specific contexts typically are considered to be contact calls. However, results from several recent studies indicate that these calls function to facilitate social interactions. White-faced capuchin monkeys (Cebus capucinus) emit a high-frequency vocalization, termed a "trill," in social interactions and during travel. In this study, immatures emitted most trills, but adult females also trilled; by contrast, adult males rarely trilled. Infants emitted the majority of trills, and they trilled at significantly higher rates than adult females. Infants trilled most when approaching other individuals. Furthermore, infants emitted proportionately more trills than other age classes when approaching other individuals. I therefore focused on the detailed context and immediate behavioral correlates of trilling by infants. Infants that trilled when approaching others tended to interact affiliatively with them subsequently (i.e., climbing on, touching, receiving grooming, and performing food inspection) more than infants that did not trill when approaching. Therefore, infant trilling may have had an immediate effect on the recipient's behavior.

Cross-site differences in foraging behavior of white-faced capuchins (Cebus capucinus).

Researchers have identified a variety of cross-site differences in the foraging behavior of free-ranging great apes, most notably among chimpanzees (Pan troglodytes) and more recently orangutans (Pongo pygmaeus), that are not due to obvious genetic or ecological differences. These differences are often referred to as "traditions." What is not known is whether this high level of interpopulation variation in behavior is limited to hominoids. In this study, we use long-term data from three Costa Rican field sites that are geographically close and similar ecologically to identify potential foraging traditions in white-faced capuchins (Cebus capucinus). Foraging traditions are predicted in Cebus because of many behavioral and morphological convergences between this genus and the great apes. The processing techniques used for the same food species were compared across sites, and all differences found were classified as present, habitual, or customary. Proximity data were also analyzed to determine if social learning mechanisms could explain variation in foraging behavior. Of the 61 foods compared, we found that 20 of them are processed differently by capuchins across sites. The differences involve pound, rub, tap, "fulcrum," "leaf-wrap," and "army ant following." For most of the differences with enough data to analyze, the average proximity score of the "matched" dyads (two individuals within a group who shared a "different" processing technique) was statistically higher than the average proximity score of the remaining "unmatched" dyads.

Number of males in primate groups: Comparative tests of competing hypotheses.

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternatively, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size. © 1996 Wiley-Liss, Inc.

Dialects in wild chimpanzees?

Chimpanzees emit a loud, species-typical long distance call known as the pant hoot. Geographic variation between the pant hoots of chimpanzees living in two neighboring populations, the Mahale Mountains and Gombe Stream National Parks, Tanzania, was examined. Analysis of six acoustic features revealed subtle differences in the way chimpanzees from the two populations called. Individuals from the Mahale study site uttered one section of their pant hoots at a faster rate and with shorter elements than animals from Gombe Stream. In addition, individuals at Mahale delivered broader-band, higher pitched "climax" elements than males from Gombe. While genetic factors, anatomical differences, variations in the use of calls at the two sites, and changes in calling over time may account for the variability between populations, we suggest the additional possibility that differences in pant hooting may be due to learning. © 1992 Wiley-Liss, Inc.