Contact calls of common marmosets (Callithrix jacchus): influence of age of caller on antiphonal calling and other vocal responses

Features of animal babbling in the vocal ontogeny of the gray mouse lemur (Microcebus murinus)

In human infants babbling is an important developmental stage of vocal plasticity to acquire maternal language. To investigate parallels in the vocal development of human infants and non-human mammals, seven key features of human babbling were defined, which are up to date only shown in bats and marmosets. This study will explore whether these features can also be found in gray mouse lemurs by investigating how infant vocal streams gradually resemble the structure of the adult trill call, which is not present at birth. Using unsupervised clustering, we distinguished six syllable types, whose sequential order gradually reflected the adult trill. A subset of adult syllable types was produced by several infants, with the syllable production being rhythmic, repetitive, and independent of the social context. The temporal structure of the calling bouts and the tempo-spectral features of syllable types became adult-like at the age of weaning. The age-dependent changes in the acoustic parameters differed between syllable types, suggesting that they cannot solely be explained by physical maturation of the vocal apparatus. Since gray mouse lemurs exhibit five features of animal babbling, they show parallels to the vocal development of human infants, bats, and marmosets.

Social factors drive vocal exchanges in red-capped mangabeys (Cercocebus torquatus)

Of all the calls made by non-human primates, the function of short-distance contact calls has largely remained to be determined. These calls are the most frequent in the repertoire and are most often exchanged between individuals in a non-random way. To our knowledge, no study has ever examined how vocal exchanges are structured in red-capped mangabeys (Cercocebus torquatus), a semi-terrestrial monkey living in the African forest with a complex semi-tolerant/semi-despotic social system. Our goal was to assess the organization of contact call exchanges in this species and their relationship with individual and social factors such as age, affinity, and hierarchy. Therefore, we observed several captive groups of red-capped mangabeys and collected data on vocal behavior, as well as grooming, agonistic behavior, and spatial proximity. We defined a vocal exchange in this species as a series of contact calls made by two or more individuals within a maximum inter-caller interval of 2 s. At the individual level, the higher the individual's hierarchical rank, the less they initiated exchanges. Furthermore, the most socially integrated individuals had a longer average response time than the less integrated ones. At the dyadic level, preferred exchange partners were individuals often observed near one other or individuals most distant in age. Also, the further apart two individuals were in the dominance hierarchy, the shorter the response time. Our results support both the social bonding hypothesis and a modulating key role of the dominance hierarchy on the social use of contact calls, which is in line with the social style of this species.

A prosocial function of head-gaze aversion and head-cocking in common marmosets

Gaze aversion is a behavior adopted by several mammalian and non-mammalian species in response to eye contact, and is usually interpreted as a reaction to a perceived threat. Unlike many other primate species, common marmosets (Callithrix jacchus) are thought to have a high tolerance for direct gaze, barely exhibiting gaze avoidance towards conspecifics and humans. Here we show that this does not hold for marmosets interacting with a familiar experimenter who suddenly establishes eye contact in a playful interaction (peekaboo). Video footage synchronously recorded from the perspective of the marmoset and the experimenter showed that the monkeys consistently alternated between eye contact and head-gaze aversion, and that these responses were often preceded by head-cocking. We hypothesize that this behavioral strategy helps marmosets to temporarily disengage from emotionally overwhelming social stimulation due to sight of another individual's face, in order to prepare for a new round of affiliative face-to-face interactions.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

Contact call acoustic structure is associated with inter-individual distances during antiphonal vocal exchanges in wild red-tailed monkeys (Cercopithecus ascanius schmidti)

Contact calls allow animals to maintain group cohesion when visibility is restricted. To maximise call detection, animals should produce calls that are audible to closest neighbours or respond to individuals that produce preceding calls (i.e., antiphony). Antiphonal exchanges are more likely to occur between older conspecifics that respond more reliably or close neighbours that are more likely to detect calls when groups are travelling. Because animals should produce calls that are optimised for propagation, call structure should be associated with the distance between individuals calling in antiphonal exchanges. I investigated whether acoustic structures of red-tailed monkey (Cercopithecus ascanius) contact calls (phrased grunts) reflected increased sound propagation as nearest neighbour distances increased, depending on three factors: (1) the occurrence of a preceding grunt, (2) neighbour age-sex class, and (3) group travel speed. I recorded grunts from five habituated monkey groups at Kibale National Park, Uganda. Per grunt, I measured five parameters associated with sound propagation. Grunt mean entropy and frequency related negatively to neighbour distance when the neighbour produced a preceding grunt or when there was no preceding grunt, but not when a more distant individual grunted prior. Neighbour age-sex class and group travel speed did not influence whether grunt structure was associated with neighbour distance, but monkeys produced grunts with higher mean entropy and frequency as groups travelled faster. Variation in grunt mean entropy and frequency was associated with propagation to either nearest neighbours or more distant individuals that produced preceding calls, providing quantitative evidence for antiphonal calling. By calling antiphonally, animals in cohesive groups can spread out to avoid intra-group competition while maintaining contact with other group members. Higher grunt entropy and frequency as groups travel faster may counteract more variable sound attenuation as animals move through acoustically complex (e.g., densely vegetated) environments.

Vocalization associated respiration patterns: thermography-based monitoring and detection of preparation for calling

Vocal emission requires coordination with the respiratory system. Monitoring the increase in laryngeal pressure, which is needed for vocal production, allows detection of transitions from quiet respiration to vocalization-supporting respiration. Characterization of these transitions could be used to identify preparation for vocal emission and to examine the probability of it manifesting into an actual vocal production event. Specifically, overlaying the subject's respiration with conspecific calls can highlight events of call initiation and suppression, as a means of signalling coordination and avoiding jamming. Here, we present a thermal imaging-based methodology for synchronized respiration and vocalization monitoring of free-ranging meerkats. The sensitivity of this methodology is sufficient for detecting transient changes in the subject's respiration associated with the exertion of vocal production. The differences in respiration are apparent not only during the vocal output, but also prior to it, marking the potential time frame of the respiratory preparation for calling. A correlation between conspecific calls with elongation of the focal subject's respiration cycles could be related to fluctuations in attention levels or in the motivation to reply. This framework can be used for examining the capability for enhanced respiration control in animals during modulated and complex vocal sequences, detecting ‘failed’ vocalization attempts and investigating the role of respiration cues in the regulation of vocal interactions.

Summary: A thermography-based methodology for estimating breathing traces in free-ranging meerkats detects changes in respiration associated with the preparation and with the production of vocal signals by combining respiration monitoring with audio recordings.

Social pressure drives "conversational rules" in great apes

In the last decade, two hypotheses, one on the evolution of animal vocal communication in general and the other on the origins of human language, have gained ground. The first hypothesis argues that the complexity of communication co-evolved with the complexity of sociality. Species forming larger groups with complex social networks have more elaborate vocal repertoires. The second hypothesis posits that the core of communication is represented not only by what can be expressed by an isolated caller, but also by the way that vocal interactions are structured, language being above all a social act. Primitive forms of conversational rules based on a vocal turn-taking principle are thought to exist in primates. To support and bring together these hypotheses, more comparative studies of socially diverse species at different levels of the primate phylogeny are needed. However, the majority of available studies focus on monkeys, primates that are distant from the human lineage. Great apes represent excellent candidates for such comparative studies because of their phylogenetic proximity to humans and their varied social lives. We propose that studying vocal turn-taking in apes could address several major gaps regarding the social relevance of vocal turn-taking and the evolutionary trajectory of this behaviour among anthropoids. Indeed, how the social structure of a species may influence the vocal interaction patterns observed among group members remains an open question. We gathered data from the literature as well as original unpublished data (where absent in the literature) on four great ape species: chimpanzees Pan troglodytes, bonobos Pan paniscus, western lowland gorillas Gorilla gorilla gorilla and Bornean orang-utans Pongo pygmaeus. We found no clear-cut relationship between classical social complexity metrics (e.g. number of group members, interaction rates) and vocal complexity parameters (e.g. repertoire size, call rates). Nevertheless, the nature of the society (i.e. group composition, diversity and valence of social bonds) and the type of vocal interaction patterns (isolated calling, call overlap, turn-taking-based vocal exchanges) do appear to be related. Isolated calling is the main vocal pattern found in the species with the smallest social networks (orang-utan), while the other species show vocal interactions that are structured according to temporal rules. A high proportion of overlapping vocalisations is found in the most competitive species (chimpanzee), while vocal turn-taking predominates in more tolerant bonobos and gorillas. Also, preferentially interacting individuals and call types used to interact are not randomly distributed. Vocal overlap ('chorusing') and vocal exchange ('conversing') appear as possible social strategies used to advertise/strengthen social bonds. Our analyses highlight that: (i) vocal turn-taking is also observed in non-human great apes, revealing universal rules for conversing that may be deeply rooted in the primate lineage; (ii) vocal interaction patterns match the species' social lifestyle; (iii) although limited to four species here, adopting a targeted comparative approach could help to identify the multiple and subtle factors underlying social and vocal complexity. We believe that vocal interaction patterns form the basis of a promising field of investigation that may ultimately improve our understanding of the socially driven evolution of communication.

Breaking conversational rules matters to captive gorillas: A playback experiment

Across human cultures, conversations are regulated by temporal and social rules. The universality of conversational rules suggests possible biological bases and encourages comparisons with the communicative interactions of nonhuman animals. Unexpectedly, few studies have focused on other great apes despite evidence of proto-conversational rules in monkeys, thus preventing researchers from drawing conclusions on potential evolutionary origins of this behaviour. A previous study showed however that western lowland gorillas engage in soft call interactions that seem temporally- and socially-ruled. Indeed, interactions occurred mainly between individuals close in age who followed a preset response delay, thus preventing call overlap. Here, we experimentally investigated the presence of these rules in a captive gorilla group, using a violation-of-expectation paradigm. Head orientation responses suggest that the respect of response delay matters to subjects, but the importance of the interlocutors' age proximity appeared less clear. The intensity of the response varied with subjects' age in a context-dependent way, supporting a possible role of learning. Our findings support the growing number of studies highlighting the importance of vocal turn-taking in animals and a possible sociogenesis of this ability. The capacity to "converse" might have been a key step in the co-evolution of communication and complex sociality.

Music and Language in Social Interaction: Synchrony, Antiphony, and Functional Origins

Music and language are universal human abilities with many apparent similarities relating to their acoustics, structure, and frequent use in social situations. We might therefore expect them to be understood and processed similarly, and indeed an emerging body of research suggests that this is the case. But the focus has historically been on the individual, looking at the passive listener or the isolated speaker or performer, even though social interaction is the primary site of use for both domains. Nonetheless, an important goal of emerging research is to compare music and language in terms of acoustics and structure, social interaction, and functional origins to develop parallel accounts across the two domains. Indeed, a central aim of both of evolutionary musicology and language evolution research is to understand the adaptive significance or functional origin of human music and language. An influential proposal to emerge in recent years has been referred to as the social bonding hypothesis. Here, within a comparative approach to animal communication systems, I review empirical studies in support of the social bonding hypothesis in humans, non-human primates, songbirds, and various other mammals. In support of this hypothesis, I review six research fields: (i) the functional origins of music; (ii) the functional origins of language; (iii) mechanisms of social synchrony for human social bonding; (iv) language and social bonding in humans; (v) music and social bonding in humans; and (vi) pitch, tone and emotional expression in human speech and music. I conclude that the comparative study of complex vocalizations and behaviors in various extant species can provide important insights into the adaptive function(s) of these traits in these species, as well as offer evidence-based speculations for the existence of "musilanguage" in our primate ancestors, and thus inform our understanding of the biology and evolution of human music and language.

Optimal features for auditory categorization

Humans and vocal animals use vocalizations to communicate with members of their species. A necessary function of auditory perception is to generalize across the high variability inherent in vocalization production and classify them into behaviorally distinct categories ('words' or 'call types'). Here, we demonstrate that detecting mid-level features in calls achieves production-invariant classification. Starting from randomly chosen marmoset call features, we use a greedy search algorithm to determine the most informative and least redundant features necessary for call classification. High classification performance is achieved using only 10-20 features per call type. Predictions of tuning properties of putative feature-selective neurons accurately match some observed auditory cortical responses. This feature-based approach also succeeds for call categorization in other species, and for other complex classification tasks such as caller identification. Our results suggest that high-level neural representations of sounds are based on task-dependent features optimized for specific computational goals.

Social bonding drives vocal exchanges in Bonobos

The origin of human speech is still a hotly debated topic in science. Evidence of socially-guided acoustic flexibility and proto-conversational rules has been found in several monkey species, but is lacking in social and cooperative great apes. Here we investigated spontaneous vocal interactions within a peaceful context in captive bonobos to reveal that vocal interactions obey temporally and social rules. Dyadic vocal interactions were characterized by call overlap avoidance and short inter-call intervals. Bonobos preferentially responded to conspecifics with whom they maintained close bonds. We also found that vocal sharing rate (production rate of shared acoustic variants within each given dyad) was mostly explained by the age difference of callers, as other individual characteristics (sex, kinship) and social parameters (affinity in spatial proximity and in vocal interactions) were not. Our results show that great apes spontaneously display primitive conversation rules guided by social bonds. The demonstration that such coordinated vocal interactions are shared between monkeys, apes and humans fills a significant gap in our knowledge of vocal communication within the primate phylogeny and highlights the universal feature of social influence in vocal interactions.

Classification of producer characteristics in primate long calls using neural networks

Primate long calls are high-amplitude vocalizations that can be critical in maintaining intragroup contact and intergroup spacing, and can encode abundant information about a call's producer, such as age, sex, and individual identity. Long calls of the wild emperor (Saguinus imperator) and saddleback (Leontocebus weddelli) tamarins were tested for these identity signals using artificial neural networks, machine-learning models that reduce subjectivity in vocalization classification. To assess whether modelling could be streamlined by using only factors which were responsible for the majority of variation within networks, each series of networks was re-trained after implementing two methods of feature selection. First, networks were trained and run using only the subset of variables whose weights accounted for ≥50% of each original network's variation, as identified by the networks themselves. In the second, only variables implemented by decision trees in predicting outcomes were used. Networks predicted dependent variables above chance (≥58.7% for sex, ≥69.2 for age class, and ≥38.8% for seven to eight individuals), but classification accuracy was not markedly improved by feature selection. Findings are discussed with regard to implications for future studies on identity signaling in vocalizations and streamlining of data analysis.

Food Calls in Common Marmosets, Callithrix jacchus, and Evidence That One Is Functionally Referential

We studied three calls of common marmosets, Callithrix jacchus, elicited in the context of food. Call A, but not B or C, had been described previously as a food call. We presented insects (live mealworms or crickets) and fruit (banana or blueberries) and used playbacks of calls. We found that Call C was produced only in response to seeing insects, and not fruit; it consistently signaled the availability of insects (includes mealworms), and more so when this food could be seen but not consumed. Playback of Call C caused the marmosets to stop feeding on a less preferred food (banana) and, instead, go to inspect a location where mealworms had been found previously, providing evidence that it has referential meaning. No such immediate response was elicited on hearing Call A or background noise. Call A differed from C in that it was produced more frequently when the marmosets were consuming the food than when they could only see it, and call A showed no specificity between insects and fruit. Call B was emitted less frequently than the A or C calls and, by the marmosets that were tested alone, most often to crickets. An audience effect occurred, in that all three calls were emitted more often when the marmosets were tested alone than when in pairs. Recognition of the functional significance of marmoset calls can lead to improved husbandry of marmosets in captivity.

Taking turns: bridging the gap between human and animal communication

Language, humans' most distinctive trait, still remains a 'mystery' for evolutionary theory. It is underpinned by a universal infrastructure-cooperative turn-taking-which has been suggested as an ancient mechanism bridging the existing gap between the articulate human species and their inarticulate primate cousins. However, we know remarkably little about turn-taking systems of non-human animals, and methodological confounds have often prevented meaningful cross-species comparisons. Thus, the extent to which cooperative turn-taking is uniquely human or represents a homologous and/or analogous trait is currently unknown. The present paper draws attention to this promising research avenue by providing an overview of the state of the art of turn-taking in four animal taxa-birds, mammals, insects and anurans. It concludes with a new comparative framework to spur more research into this research domain and to test which elements of the human turn-taking system are shared across species and taxa.

Individual identity and affective valence in marmoset calls: in vivo brain imaging with vocal sound playback

As with humans, vocal communication is an important social tool for nonhuman primates. Common marmosets (Callithrix jacchus) often produce whistle-like 'phee' calls when they are visually separated from conspecifics. The neural processes specific to phee call perception, however, are largely unknown, despite the possibility that these processes involve social information. Here, we examined behavioral and whole-brain mapping evidence regarding the detection of individual conspecific phee calls using an audio playback procedure. Phee calls evoked sound exploratory responses when the caller changed, indicating that marmosets can discriminate between caller identities. Positron emission tomography with [18F] fluorodeoxyglucose revealed that perception of phee calls from a single subject was associated with activity in the dorsolateral prefrontal, medial prefrontal, orbitofrontal cortices, and the amygdala. These findings suggest that these regions are implicated in cognitive and affective processing of salient social information. However, phee calls from multiple subjects induced brain activation in only some of these regions, such as the dorsolateral prefrontal cortex. We also found distinctive brain deactivation and functional connectivity associated with phee call perception depending on the caller change. According to changes in pupillary size, phee calls from a single subject induced a higher arousal level compared with those from multiple subjects. These results suggest that marmoset phee calls convey information about individual identity and affective valence depending on the consistency or variability of the caller. Based on the flexible perception of the call based on individual recognition, humans and marmosets may share some neural mechanisms underlying conspecific vocal perception.

Of Men and Mice: Modeling the Fragile X Syndrome

The Fragile X Syndrome (FXS) is one of the most common forms of inherited intellectual disability in all human societies. Caused by the transcriptional silencing of a single gene, the fragile x mental retardation gene FMR1, FXS is characterized by a variety of symptoms, which range from mental disabilities to autism and epilepsy. More than 20 years ago, a first animal model was described, the Fmr1 knock-out mouse. Several other models have been developed since then, including conditional knock-out mice, knock-out rats, a zebrafish and a drosophila model. Using these model systems, various targets for potential pharmaceutical treatments have been identified and many treatments have been shown to be efficient in preclinical studies. However, all attempts to turn these findings into a therapy for patients have failed thus far. In this review, I will discuss underlying difficulties and address potential alternatives for our future research.

Audience affects decision-making in a marmoset communication network

An audience can have a profound effect on the dynamics of communicative interactions. As a result, non-human primates often adjust their social decision-making strategies depending on the audience composition at a given time. Here we sought to test how the unique vocal behaviour of multiple audience members affected decisions to communicate. To address this issue, we developed a novel experimental paradigm in which common marmosets directly interacted with multiple 'virtual monkeys' (VMs), each of whom represented an individual marmoset with distinct vocal behaviour. This active social signalling paradigm provided subjects an opportunity to interact with and learn about the behaviour of each VM in the network and apply this knowledge in subsequent communicative decisions. We found that subjects' propensity to interact with particular VMs was determined by the behaviour of each VM in the audience and suggests that marmoset social decision-making strategies are highly adaptive to nuances of the immediate communication network.

Call rates of mothers change with maternal experience and with infant characteristics in free-ranging gray-cheeked mangabeys

Studies have shown that becoming a mother triggers important social changes within females, according to both social experience and infant characteristics, showing different maternal concerns. But how this impacts call usage has been far less studied. Based on 6 months of observations of five free-ranging groups of gray-cheeked mangabeys, we investigated variations in the production of three call types (contact, excitement, and alarm calls) in 29 females of different ages, dominance ranks, and infant rearing experiences: 15 females with infants of different ages and sexes, and 14 females without infants. We found that in females with infants-both maternal and infant characteristics influenced call production in a call type-dependent way. Females produced contact calls at a higher rate during the first month of infant age and after weaning when infants start to move away. Mothers of daughters produced more contact calls than mothers of sons. More excitement calls were recorded for first-time and young mothers and for females with young infants, while alarm call rates were not influenced by any of these factors. Increased mother-infant spatial separation enhanced only contact and excitement call rates. Finally, we found that females with infants vocalized much more than females without infants. Our results contribute to the current debate about the social factors responsible for the flexibility of call usage in nonhuman primates and open new lines for research on mothering behavior in forest-dwelling species. Am. J. Primatol. 78:983-991, 2016. © 2016 Wiley Periodicals, Inc.

Marmosets: A Neuroscientific Model of Human Social Behavior

The common marmoset (Callithrix jacchus) has garnered interest recently as a powerful model for the future of neuroscience research. Much of this excitement has centered on the species' reproductive biology and compatibility with gene editing techniques, which together have provided a path for transgenic marmosets to contribute to the study of disease as well as basic brain mechanisms. In step with technical advances is the need to establish experimental paradigms that optimally tap into the marmosets' behavioral and cognitive capacities. While conditioned task performance of a marmoset can compare unfavorably with rhesus monkey performance on conventional testing paradigms, marmosets' social behavior and cognition are more similar to that of humans. For example, marmosets are among only a handful of primates that, like humans, routinely pair bond and care cooperatively for their young. They are also notably pro-social and exhibit social cognitive abilities, such as imitation, that are rare outside of the Apes. In this Primer, we describe key facets of marmoset natural social behavior and demonstrate that emerging behavioral paradigms are well suited to isolate components of marmoset cognition that are highly relevant to humans. These approaches generally embrace natural behavior, which has been rare in conventional primate testing, and thus allow for a new consideration of neural mechanisms underlying primate social cognition and signaling. We anticipate that through parallel technical and paradigmatic advances, marmosets will become an essential model of human social behavior, including its dysfunction in neuropsychiatric disorders.

Social coordination in animal vocal interactions. Is there any evidence of turn-taking? The starling as an animal model

Turn-taking in conversation appears to be a common feature in various human cultures and this universality raises questions about its biological basis and evolutionary trajectory. Functional convergence is a widespread phenomenon in evolution, revealing sometimes striking functional similarities between very distant species even though the mechanisms involved may be different. Studies on mammals (including non-human primates) and bird species with different levels of social coordination reveal that temporal and structural regularities in vocal interactions may depend on the species' social structure. Here we test the hypothesis that turn-taking and associated rules of conversations may be an adaptive response to the requirements of social life, by testing the applicability of turn-taking rules to an animal model, the European starling. Birdsong has for many decades been considered as one of the best models of human language and starling songs have been well described in terms of vocal production and perception. Starlings do have vocal interactions where alternating patterns predominate. Observational and experimental data on vocal interactions reveal that (1) there are indeed clear temporal and structural regularities, (2) the temporal and structural patterning is influenced by the immediate social context, the general social situation, the individual history, and the internal state of the emitter. Comparison of phylogenetically close species of Sturnids reveals that the alternating pattern of vocal interactions varies greatly according to the species' social structure, suggesting that interactional regularities may have evolved together with social systems. These findings lead to solid bases of discussion on the evolution of communication rules in relation to social evolution. They will be discussed also in terms of processes, at the light of recent neurobiological findings.

The evolution of speech: vision, rhythm, cooperation

A full account of human speech evolution must consider its multisensory, rhythmic, and cooperative characteristics. Humans, apes, and monkeys recognize the correspondence between vocalizations and their associated facial postures, and gain behavioral benefits from them. Some monkey vocalizations even have a speech-like acoustic rhythmicity but lack the concomitant rhythmic facial motion that speech exhibits. We review data showing that rhythmic facial expressions such as lip-smacking may have been linked to vocal output to produce an ancestral form of rhythmic audiovisual speech. Finally, we argue that human vocal cooperation (turn-taking) may have arisen through a combination of volubility and prosociality, and provide comparative evidence from one species to support this hypothesis.

Convergent evolution of vocal cooperation without convergent evolution of brain size

One pragmatic underlying successful vocal communication is the ability to take turns. Taking turns - a form of cooperation - facilitates the transmission of signals by reducing the amount of their overlap. This allows vocalizations to be better heard. Until recently, non-human primates were not thought of as particularly cooperative, especially in the vocal domain. We recently demonstrated that common marmosets (Callithrix jacchus), a small New World primate species, take turns when they exchange vocalizations with both related and unrelated conspecifics. As the common marmoset is distantly related to humans (and there is no documented evidence that Old World primates exhibit vocal turn taking), we argue that this ability arose as an instance of convergent evolution, and is part of a suite of prosocial behavioral tendencies. Such behaviors seem to be, at least in part, the outcome of the cooperative breeding strategy adopted by both humans and marmosets. Importantly, this suite of shared behaviors occurs without correspondence in encephalization. Marmoset vocal turn taking demonstrates that a large brain size and complex cognitive machinery is not needed for vocal cooperation to occur. Consistent with this idea, the temporal structure of marmoset vocal exchanges can be described in terms of coupled oscillator dynamics, similar to quantitative descriptions of human conversations. We propose a simple neural circuit mechanism that may account for these dynamics and, at its core, involves vocalization-induced reductions of arousal. Such a mechanism may underlie the evolution of vocal turn taking in both marmoset monkeys and humans.

Coupled oscillator dynamics of vocal turn-taking in monkeys

Cooperation is central to human communication. The foundation of cooperative verbal communication is taking turns to speak. Given the universality of turn-taking, it is natural to ask how it evolved. We used marmoset monkeys to explore whether another primate species exhibits cooperative vocal communication by taking turns. Marmosets share with humans a cooperative breeding strategy and volubility. Cooperative care behaviors are thought to scaffold prosocial cognitive processes. Moreover, marmosets and other callitrichid primates are very vocal and readily exchange vocalizations with conspecifics. By measuring the natural statistics of marmoset vocal exchanges, we observed that they take turns in extended sequences and show that this vocal turn-taking has as its foundation dynamics characteristic of coupled oscillators--one that is similar to the dynamics proposed for human conversational turn-taking. As marmoset monkeys are on a different branch of the evolutionary tree that led to humans, our data demonstrate convergent evolution of vocal cooperation. Perhaps more importantly, our data offer a plausible alternative scenario to "gestural origin" hypotheses for how human cooperative vocal communication could have evolved.

How Twitter Is Studied in the Medical Professions: A Classification of Twitter Papers Indexed in PubMed

Background

Since their inception, Twitter and related microblogging systems have provided a rich source of information for researchers and have attracted interest in their affordances and use. Since 2009 PubMed has included 123 journal articles on medicine and Twitter, but no overview exists as to how the field uses Twitter in research.

Objective

This paper aims to identify published work relating to Twitter within the fields indexed by PubMed, and then to classify it. This classification will provide a framework in which future researchers will be able to position their work, and to provide an understanding of the current reach of research using Twitter in medical disciplines.

Methods

Papers on Twitter and related topics were identified and reviewed. The papers were then qualitatively classified based on the paper’s title and abstract to determine their focus. The work that was Twitter focused was studied in detail to determine what data, if any, it was based on, and from this a categorization of the data set size used in the studies was developed. Using open coded content analysis additional important categories were also identified, relating to the primary methodology, domain, and aspect.

Results

As of 2012, PubMed comprises more than 21 million citations from biomedical literature, and from these a corpus of 134 potentially Twitter related papers were identified, eleven of which were subsequently found not to be relevant. There were no papers prior to 2009 relating to microblogging, a term first used in 2006. Of the remaining 123 papers which mentioned Twitter, thirty were focused on Twitter (the others referring to it tangentially). The early Twitter focused papers introduced the topic and highlighted the potential, not carrying out any form of data analysis. The majority of published papers used analytic techniques to sort through thousands, if not millions, of individual tweets, often depending on automated tools to do so. Our analysis demonstrates that researchers are starting to use knowledge discovery methods and data mining techniques to understand vast quantities of tweets: the study of Twitter is becoming quantitative research.

Conclusions

This work is to the best of our knowledge the first overview study of medical related research based on Twitter and related microblogging. We have used 5 dimensions to categorize published medical related research on Twitter. This classification provides a framework within which researchers studying development and use of Twitter within medical related research, and those undertaking comparative studies of research, relating to Twitter in the area of medicine and beyond, can position and ground their work.

Influence of different light intensities on the daily grooming distribution of common marmosets Callithrix jacchus

The daily distribution of autogrooming was evaluated in adult marmosets submitted to different illumination intensities in the light phase of the light-dark cycle. Autogrooming and locomotor activity were monitored and the faecal cortisol level assessed as a stress indicator. The distribution of autogrooming showed two distinct tendencies: when the light intensity varied from 500 to 200 lux, a slight increase in frequency and duration was observed, while a significant decrease in both variables occurred at 10 lux. Varying light intensities did not inhibit rhythm synchronization. The daily profile of autogrooming was mainly unimodal with an acrophase in the first half of the light phase. Faecal cortisol levels tended to increase in animals submitted to 100 and 10 lux, but these results are not conclusive. We suggest keeping captive marmosets in light intensities of at least 200 lux in the light phase, allowing animals to maintain autogrooming levels in order to reduce the discomfort caused by captivity and isolation.

The communicative content of the common marmoset phee call during antiphonal calling

Vocalizations are a dominant means of communication for numerous species, including nonhuman primates. These acoustic signals are encoded with a rich array of information available to signal receivers that can be used to guide species-typical behaviors. In this study, we examined the communicative content of common marmoset phee calls, the species-typical long distance contact call, during antiphonal calling. This call type has a relatively stereotyped acoustic structure, consisting of a series of long tonal pulses. Analyses revealed that calls could be reliably classified based on the individual identity and social group of the caller. Our analyses did not, however, correctly classify phee calls recorded under different social contexts, although differences were evident along individual acoustic parameters. Further tests of antiphonal calling interactions showed that spontaneously produced phee calls differ from antiphonal phee calls in their peak and end frequency, which may be functionally significant. Overall, this study shows that the marmoset phee call has a rich communicative content encoded in its acoustic structure available to conspecifics during antiphonal calling exchanges.

Attention to elders' voice in non-human primates

The observed respect and attention to elders' speech in traditional cultures appears to have a 'universal' component which questions its possible biological bases. Animals present differential attention to the vocalizations of other individuals according to their characteristics but little is known about the potential propensity to pay more attention to vocalizations of elders. On the basis of several hundreds of vocal exchanges recorded, here we show that aged female Campbell's monkeys (Cercopithecus campbelli), despite being significantly less 'loquacious' than their younger adult counterparts, elicit many more responses when calling. These findings show that attention to elders' vocal production appears in non-human primates, leading to new lines of questioning on human culture and language evolution.