Facial expressions in common marmosets (Callithrix jacchus) and their use by conspecifics

From masks to muscles: Mapping facial structure of Nycticebus

Facial musculature in mammals underlies mastication and nonverbal communicative facial displays. Our understanding of primate facial expression comes primarily from haplorrhines (monkeys and apes), while our understanding of strepsirrhine (lemurs and lorises) facial expression remains incomplete. We examined the facial muscles of six specimens from three Nycticebus species (Nycticebus coucang, Nycticebus javanicus, and Nycticebus menagensis) using traditional dissection methodology and novel three-dimensional facial scanning to produce a detailed facial muscle map, and compared these results to another nocturnal strepsirrhine genus, the greater bushbaby (Otolemur spp.). We observed 19 muscles with no differences among Nycticebus specimens. A total of 17 muscles were observed in both Nycticebus and Otolemur, with little difference in attachment and function but some difference in directionality of movement. In the oral region, we note the presence of the depressor anguli oris, which has been reported in other primate species but is absent in Otolemur. The remaining muscle is a previously undescribed constrictor nasalis muscle located on the lateral nasal alar region, likely responsible for constriction of the nares. We propose this newly described muscle may relate to vomeronasal organ functioning and the importance of the use of nasal musculature in olfactory communication. We discuss how this combined methodology enabled imaging of small complex muscles. We further discuss how the facial anatomy of Nycticebus spp. relates to their unique physiology and behavioral ecology.

Facial blushing and feather fluffing are indicators of emotions in domestic fowl (Gallus gallus domesticus)

The study of facial expressions in mammals provided great advances in the identification of their emotions and then in the comprehension of their sentience. So far, this area of research has excluded birds. With a naturalist approach, we analysed facial blushing and feather displays in domestic fowl. Hens were filmed in situations contrasting in emotional valence and arousal level: situations known to indicate calm states (positive valence / low arousal), have rewarding effects (positive valence / high arousal) or induce fear-related behaviour (negative valence / high arousal). Head feather position as well as skin redness of comb, wattles, ear lobes and cheeks varied across these situations. Skin of all four areas was less red in situations with low arousal compared to situations with higher arousal. Furthermore, skin redness of the cheeks and ear lobes also varied depending on the valence of the situation: redness was higher in situations with negative valence compared to situations with positive valence. Feather position also varied with the situations. Feather fluffing was mostly observed in positively valenced situations, except when hens were eating. We conclude that hens have facial displays that reveal their emotions and that blushing is not exclusive to humans. This opens a promising way to explore the emotional lives of birds, which is a critical step when trying to improve poultry welfare.

The neurobiology of vocal communication in marmosets

An increasingly popular animal model for studying the neural basis of social behavior, cognition, and communication is the common marmoset (Callithrix jacchus). Interest in this New World primate across neuroscience is now being driven by their proclivity for prosociality across their repertoire, high volubility, and rapid development, as well as their amenability to naturalistic testing paradigms and freely moving neural recording and imaging technologies. The complement of these characteristics set marmosets up to be a powerful model of the primate social brain in the years to come. Here, we focus on vocal communication because it is the area that has both made the most progress and illustrates the prodigious potential of this species. We review the current state of the field with a focus on the various brain areas and networks involved in vocal perception and production, comparing the findings from marmosets to other animals, including humans.

"The influence of olfactory enrichment on the behavior of two captive New World primates: Black-capped capuchin (Sapajus apella) and common marmoset (Callithrix jacchus)"

Environmental enrichment is an animal husbandry principle that seeks to provide the stimuli necessary for the optimal physiological and psychological well-being of animals. Due to primates having highly developed visual systems, there have been limited attempts to quantify the benefit of olfactory enrichment on captive primate populations. We aim to investigate how a range of odors may influence the behaviors of two captive New World primate species that have varying reliance on olfactory pathways, black-capped capuchin (Sapajus apella) and common marmoset (Callithrix jacchus), at the National Zoo and Aquarium, Canberra, Australia. We presented three odors (rosemary oil, Salvia rosmarinus, banana essence and white-tailed deer urine, Odocoileus virginianus) four different times to the two species following a 12-week randomized schedule. Using instantaneous scan sampling we collected behavioral and direct cloth interaction (DCI) data on 40 days. We then calculated activity budgets. Results show both species significantly respond to different olfactory conditions. S. apella responded to banana by decreasing inactivity (df = 4, F = 6.600, p = .007), and increasing DCI frequencies (df = 3, F = 116.196, p < .0001) whereas C. jacchus was influenced by rosemary and deer urine-also reducing inactivity levels (df= 4, F = 15.938, p < .0001), but not changing DCI frequencies. We also tested habituation however it is not significant for either species over the course of the study. This comparative investigation is one of the first of its kind and uncovers the possibility for olfactory stimulus to be successfully used as a type of beneficial environmental enrichment for captive primates, supporting the constructive and ongoing development of enrichment programs at captive facilities.

CalliFACS: The common marmoset Facial Action Coding System

Facial expressions are subtle cues, central for communication and conveying emotions in mammals. Traditionally, facial expressions have been classified as a whole (e.g. happy, angry, bared-teeth), due to automatic face processing in the human brain, i.e., humans categorise emotions globally, but are not aware of subtle or isolated cues such as an eyebrow raise. Moreover, the same facial configuration (e.g. lip corners pulled backwards exposing teeth) can convey widely different information depending on the species (e.g. humans: happiness; chimpanzees: fear). The Facial Action Coding System (FACS) is considered the gold standard for investigating human facial behaviour and avoids subjective interpretations of meaning by objectively measuring independent movements linked to facial muscles, called Action Units (AUs). Following a similar methodology, we developed the CalliFACS for the common marmoset. First, we determined the facial muscular plan of the common marmoset by examining dissections from the literature. Second, we recorded common marmosets in a variety of contexts (e.g. grooming, feeding, play, human interaction, veterinary procedures), and selected clips from online databases (e.g. YouTube) to identify their facial movements. Individual facial movements were classified according to appearance changes produced by the corresponding underlying musculature. A diverse repertoire of 33 facial movements was identified in the common marmoset (15 Action Units, 15 Action Descriptors and 3 Ear Action Descriptors). Although we observed a reduced range of facial movement when compared to the HumanFACS, the common marmoset's range of facial movements was larger than predicted according to their socio-ecology and facial morphology, which indicates their importance for social interactions. CalliFACS is a scientific tool to measure facial movements, and thus, allows us to better understand the common marmoset's expressions and communication. As common marmosets have become increasingly popular laboratory animal models, from neuroscience to cognition, CalliFACS can be used as an important tool to evaluate their welfare, particularly in captivity.

Modelling behaviors relevant to brain disorders in the nonhuman primate: Are we there yet?

Recent years have seen a profound resurgence of activity with nonhuman primates (NHPs) to model human brain disorders. From marmosets to macaques, the study of NHP species offers a unique window into the function of primate-specific neural circuits that are impossible to examine in other models. Examining how these circuits manifest into the complex behaviors of primates, such as advanced cognitive and social functions, has provided enormous insights to date into the mechanisms underlying symptoms of numerous neurological and neuropsychiatric illnesses. With the recent optimization of modern techniques to manipulate and measure neural activity in vivo, such as optogenetics and calcium imaging, NHP research is more well-equipped than ever to probe the neural mechanisms underlying pathological behavior. However, methods for behavioral experimentation and analysis in NHPs have noticeably failed to keep pace with these advances. As behavior ultimately lies at the junction between preclinical findings and its translation to clinical outcomes for brain disorders, approaches to improve the integrity, reproducibility, and translatability of behavioral experiments in NHPs requires critical evaluation. In this review, we provide a unifying account of existing brain disorder models using NHPs, and provide insights into the present and emerging contributions of behavioral studies to the field.

Preference and discrimination of facial expressions of humans, rats, and mice by C57 mice

Social animals likely recognize emotional expressions in other animals. Recent studies suggest that mice can visually perceive emotional expressions of other mice. In the first experiment, we measured the preference of mice for two different facial expressions (a normal facial expression and an expression of negative emotion such as pain) of rats, mice, and humans. Results revealed that mice showed a slight preference for the normal expression over the face expressing pain in the case of rats, but no preference in the case of others. In the second experiment, we trained mice to discriminate between the two facial expressions in an operant chamber with a touch screen. They could discriminate facial expressions of mice and rats, but they did not show discrimination of human facial expressions. Principal component analysis of the images of stimuli reveals negative correlation between pixel-based dissimilarity of training stimuli and the number of sessions to criterion. The mice showed generalization to novel images of the mouse faces with and without pain but did not maintain their discriminative behavior when new rat faces were shown. These results suggest that mice display category discrimination of conspecific facial expressions but not of other species.

Ketamine disrupts gaze patterns during face viewing in the common marmoset

Faces are stimuli of critical importance for primates. The common marmoset (Callithrix jacchus) is a promising model for investigations of face processing, as this species possesses oculomotor and face-processing networks resembling those of macaques and humans. Face processing is often disrupted in neuropsychiatric conditions such as schizophrenia (SZ), and thus, it is important to recapitulate underlying circuitry dysfunction preclinically. The N-methyl-d-aspartate (NMDA) noncompetitive antagonist ketamine has been used extensively to model the cognitive symptoms of SZ. Here, we investigated the effects of a subanesthetic dose of ketamine on oculomotor behavior in marmosets during face viewing. Four marmosets received systemic ketamine or saline injections while viewing phase-scrambled or intact videos of conspecifics' faces. To evaluate effects of ketamine on scan paths during face viewing, we identified regions of interest in each face video and classified locations of saccade onsets and landing positions within these areas. A preference for the snout over eye regions was observed following ketamine administration. In addition, regions in which saccades landed could be significantly predicted by saccade onset region in the saline but not the ketamine condition. Effects on saccade control were limited to an increase in saccade peak velocity in all conditions and a reduction in saccade amplitudes during viewing of scrambled videos. Thus, ketamine induced a significant disruption of scan paths during viewing of conspecific faces but limited effects on saccade motor control. These findings support the use of ketamine in marmosets for investigating changes in neural circuits underlying social cognition in neuropsychiatric disorders.NEW & NOTEWORTHY Face processing, an important social cognitive ability, is impaired in neuropsychiatric conditions such as schizophrenia. The highly social common marmoset model presents an opportunity to investigate these impairments. We administered subanesthetic doses of ketamine to marmosets to model the cognitive symptoms of schizophrenia. We observed a disruption of scan paths during viewing of conspecifics' faces. These findings support the use of ketamine in marmosets as a model for investigating social cognition in neuropsychiatric disorders.

Emotion recognition in nonhuman primates: How experimental research can contribute to a better understanding of underlying mechanisms

Recognising conspecifics' emotional expressions is important for nonhuman primates to navigate their physical and social environment. We address two possible mechanisms underlying emotion recognition: emotional contagion, the automatic matching of the observer's emotions to the emotional state of the observed individual, and cognitive empathy, the ability to understand the meaning and cause of emotional expressions while maintaining a distinction between own and others' emotions. We review experimental research in nonhuman primates to gain insight into the evolution of emotion recognition. Importantly, we focus on how emotional contagion and cognitive empathy can be studied experimentally. Evidence for aspects of cognitive empathy in different nonhuman primate lineages suggests that a wider range of primates than commonly assumed can infer emotional meaning from emotional expressions. Possibly, analogous rather than homologous evolution underlies emotion recognition. However, conclusions regarding its exact evolutionary course require more research in different modalities and species.

Advancing Autism Research From Mice to Marmosets: Behavioral Development of Offspring Following Prenatal Maternal Immune Activation

Understanding the mechanism(s) by which maternal immune activation (MIA) during gestation may disrupt neurodevelopment and increase the susceptibility for disorders such as autism spectrum disorder (ASD) or schizophrenia is a critical step in the development of better treatments and preventive measures. A large body of literature has investigated the pathophysiology of MIA in rodents. However, a translatability gap plagues pre-clinical research of complex behavioral/developmental diseases and those diseases requiring clinical diagnosis, such as ASD. While ideal for their genetic flexibility, vast reagent toolkit, and practicality, rodent models often lack important elements of ethological validity. Hence, our study aimed to develop and characterize the prenatal MIA model in marmosets. Here, we adapted the well-characterized murine maternal immune activation model. Pregnant dams were administered 5 mg/kg poly-L-lysine stabilized polyinosinic-polycytidylic acid (Poly ICLC) subcutaneously three times during gestation (gestational day 63, 65, and 67). Dams were allowed to deliver naturally with no further experimental treatments. After parturition, offspring were screened for general health and vigor, and individual assessment of communication development and social behavior was measured during neonatal or adolescent periods. Similar to rodent models, offspring subjected to MIA exhibited a disruption in patterns of communication during early development. Assessment of social behavior in a marmoset-modified 3-chamber test at 3 and 9 months of age revealed alterations in social behavior that, in some instances, was sex-dependent. Together, our data indicate that marmosets are an excellent non-human primate model for investigating the neurodevelopmental and behavioral consequences of exposure to prenatal challenges, like MIA. Additional studies are necessary to more completely characterize the effect of prenatal inflammation on marmoset development and explore therapeutic intervention strategies that may be applicable in a clinical setting.

Of Great Apes and Magpies: Initiations into Animal Behaviour

Simple Summary

Animal encounters have been favourite subjects for a long time and it would scarcely be novel to report such stories for their own sake, even though the ones told here are dramatic enough to stand on their own. The questions addressed in this paper are twofold. The first question is: What influence may particular and dramatic animal encounters have on the human observer and how dependent is such a response on previously held attitudes? This paper provides three cases studies of extraordinary moments that changed the lives of the human participants and turned them into advocates of the species they had encountered. The next question asked is how we can be respectful of animals without anthropomorphising them and study them in ways that help us understand their abilities and their needs rather than impose questions that mean much to the human researcher but could be irrelevant to the species? The examples given here compare and contrast species that are especially close to us (great apes) with studies of those that are distant from us in their evolution (birds) and show how different attitudes change the questions that can be asked by scientists, demonstrably leading to new and even stunning results.

Abstract

This paper presents three case studies of exceptional human encounters with animals. These particular examples were selected because they enabled analysis of the underlying reasons that led the human participants to respond in new ways to their animal counterparts. The question asked here is whether sudden insights into the needs and abilities of an animal arises purely from an anthropocentric position as empathy because of genetic closeness (e.g., chimpanzees) or is something else and whether new insights can be applied to other phylogenetic orders not close to us, e.g., birds, and change research questions and implicit prejudices and stereotypes. Particularly in avian species, phylogenetically distant from humans, the prejudices (anthroprocentric position) and the belief in human uniqueness (human exceptionalism) might be greater than in the reactions to primates. Interestingly, in studies of great apes, contradictory opinions and controversies about cognitive abilities, especially when compared with humans, tend to be pronounced. Species appropriateness in test designs are desirable present and future goals but here it is suggested how different experiences can also lead to different questions that explode the myth of human uniqueness and then arrive at entirely different and new results in cognitive and affective abilities of the species under investigation.

Face selective patches in marmoset frontal cortex

In humans and macaque monkeys, socially relevant face processing is accomplished via a distributed functional network that includes specialized patches in frontal cortex. It is unclear whether a similar network exists in New World primates, who diverged ~35 million years from Old World primates. The common marmoset is a New World primate species ideally placed to address this question given their complex social repertoire. Here, we demonstrate the existence of a putative high-level face processing network in marmosets. Like Old World primates, marmosets show differential activation in anterior cingulate and lateral prefrontal cortices while they view socially relevant videos of marmoset faces. We corroborate the locations of these frontal regions by demonstrating functional and structural connectivity between these regions and temporal lobe face patches. Given the evolutionary separation between macaques and marmosets, our results suggest this frontal network specialized for social face processing predates the separation between Platyrrhini and Catarrhini.

In Old World primates, socially relevant face processing is accomplished via a distributed functional network including specialized patches in the frontal cortex. Here, the authors demonstrate a similar network in frontal cortex of New World marmoset monkeys, suggesting inheritance from a common ancestor.

The development of communication in alarm contexts in wild chimpanzees

ABSTRACT

Animals have evolved a range of communicative behaviours in the presence of danger. Although the mechanisms and functions of some of these behaviours have been relatively well researched, comparatively little is known about their ontogeny, including how animals learn to inform social partners about impending danger. In adult chimpanzees, behaviours in response to dangers involve several channels, particularly alarm calls and simultaneous gaze alternations with nearby recipients. Gaze alternations may allow inexperienced individuals to learn from more experienced ones by assessing their reactions to unfamiliar objects or events, but they may also provide the basis for more advanced social referencing. Here, we were interested in the development of these two common behaviours, alarm calling and gaze alternations, in wild chimpanzees (Pan troglodytes schweinfurthii) confronted with a threat. Using a cross-sectional design, we investigated those in 8 infant and 8 juveniles by experimentally exposing them to an unfamiliar but potentially dangerous object, a large, remotely controlled, moving spider model. For alarm calling, we found a positive relation with age, starting at around 28 months, although alarm calls were not consistently emitted until after 80 months. For gaze alternations, we found no age effect, with some of the youngest infants already showing the behaviour. Although its function remains unclear in infant and juvenile chimpanzees, gaze alternations emerge early in chimpanzee development. Alarm calling may require more advanced developmental stages, such as greater perceptual abilities, categorical capacities or more sophisticated social cognition, i.e. an understanding that danger is a collective experience that requires communication.

SIGNIFICANCE STATEMENT

Alarm calling and other anti-predatory behaviours have been the topic of much research but their ontogenies are still poorly described and understood. Recent studies on the behaviour of wild chimpanzees in threatening contexts have suggested sophisticated social cognitive abilities in adults. How do these behaviours develop in ontogeny? We addressed this question using a field experiment with 8 infants and 8 juveniles exposed to a novel and potentially threatening object in their natural habitat. We found that gaze alternations are present in some of the youngest individuals, potentially revealing early social awareness in chimpanzees. Age did not have an effect on the presence of gaze alternation. We also found that alarm calling was more common in older individuals, suggesting that call production and context of usage must be learnt. We discuss our results in light of developmental theories of social cognition and the role of social learning in the primate lineage.

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.

The common marmoset: An overview of its natural history, ecology and behavior

Callithrix jacchus are small-bodied Neotropical primates popularly known as common marmosets. They are endemic to Northeast Brazil and occur in contrasting environments such as the humid Atlantic Forest and the dry scrub forest of the Caatinga. Common marmosets live in social groups, usually containing only one breeding pair. These primates have a parental care system in which individuals help by providing assistance to the infants even when they are not related to them. Free-ranging groups use relatively small home ranges (0.5-5 hectares) and have an omnivorous diet. Because of the shape of their teeth, they actively gouge tree bark to extract and consume exudates. When foraging for live prey, they adjust their strategy according to the type of prey. The successful use of appropriate hunting strategies depends not only on age but also on prey type and seems to be mediated by learning and experience. Indeed, common marmosets have shown unexpected cognitive abilities, such as true imitation. All these aspects seem to have contributed to the ecological success of this species. Callithrix jacchus has been widely studied, especially in captivity; even so, a number of questions remain to be answered about its biology, ecology, and behavior, both in captivity and the wild. A richer understanding of marmosets' natural behavior and ecology can have a significant impact on shaping ongoing and future neuroscience research. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 244-262, 2017.

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.

How good is this food? A study on dogs' emotional responses to a potentially pleasant event using infrared thermography

Understanding how animals express positive emotions is becoming an interesting and promising area of research in the study of animal emotions and affective experiences. In the present study, we used infrared thermography in combination with behavioral measures, heart rate (HR) and heart rate variability (HRV), to investigate dogs' emotional responses to a potentially pleasant event: receiving palatable food from the owner. Nineteen adult pet dogs, 8 females and 11 males, were tested and their eye temperature, HR, HRV and behavior were recorded during a 30-minutestestconsisting of three 10-minute consecutive phases: Baseline (Phase 1), positive stimulation through the administration of palatable treats (Feeding, Phase 2) and Post-feeding condition following the positive stimulation (Phase 3). Dogs' eye temperature and mean HR significantly increased during the positive stimulation phase compared with both Baseline and Post-feeding phases. During the positive stimulation with food (Phase 2), dogs engaged in behaviors indicating a positive emotional state and a high arousal, being focused on food treats and increasing tail wagging. However, there was no evidence of an increase in HRV during Phase 2 compared to the Phase 1, with SDNN significantly increasing only in Phase 3, after the positive stimulation occurred. Overall results point out that IRT may be a useful tool in assessing emotional states in dogs in terms of arousal but fails to discriminate emotional valence, whose interpretation cannot disregard behavioral indexes.

Social Use of Facial Expressions in Hylobatids

Non-human primates use various communicative means in interactions with others. While primate gestures are commonly considered to be intentionally and flexibly used signals, facial expressions are often referred to as inflexible, automatic expressions of affective internal states. To explore whether and how non-human primates use facial expressions in specific communicative interactions, we studied five species of small apes (gibbons) by employing a newly established Facial Action Coding System for hylobatid species (GibbonFACS). We found that, despite individuals often being in close proximity to each other, in social (as opposed to non-social contexts) the duration of facial expressions was significantly longer when gibbons were facing another individual compared to non-facing situations. Social contexts included grooming, agonistic interactions and play, whereas non-social contexts included resting and self-grooming. Additionally, gibbons used facial expressions while facing another individual more often in social contexts than non-social contexts where facial expressions were produced regardless of the attentional state of the partner. Also, facial expressions were more likely ‘responded to’ by the partner’s facial expressions when facing another individual than non-facing. Taken together, our results indicate that gibbons use their facial expressions differentially depending on the social context and are able to use them in a directed way in communicative interactions with other conspecifics.

The marmoset monkey as a model for visual neuroscience

The common marmoset (Callithrix jacchus) has been valuable as a primate model in biomedical research. Interest in this species has grown recently, in part due to the successful demonstration of transgenic marmosets. Here we examine the prospects of the marmoset model for visual neuroscience research, adopting a comparative framework to place the marmoset within a broader evolutionary context. The marmoset's small brain bears most of the organizational features of other primates, and its smooth surface offers practical advantages over the macaque for areal mapping, laminar electrode penetration, and two-photon and optical imaging. Behaviorally, marmosets are more limited at performing regimented psychophysical tasks, but do readily accept the head restraint that is necessary for accurate eye tracking and neurophysiology, and can perform simple discriminations. Their natural gaze behavior closely resembles that of other primates, with a tendency to focus on objects of social interest including faces. Their immaturity at birth and routine twinning also makes them ideal for the study of postnatal visual development. These experimental factors, together with the theoretical advantages inherent in comparing anatomy, physiology, and behavior across related species, make the marmoset an excellent model for visual neuroscience.

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.

Active vision in marmosets: a model system for visual neuroscience

The common marmoset (Callithrix jacchus), a small-bodied New World primate, offers several advantages to complement vision research in larger primates. Studies in the anesthetized marmoset have detailed the anatomy and physiology of their visual system (Rosa et al., 2009) while studies of auditory and vocal processing have established their utility for awake and behaving neurophysiological investigations (Lu et al., 2001a,b; Eliades and Wang, 2008a,b; Osmanski and Wang, 2011; Remington et al., 2012). However, a critical unknown is whether marmosets can perform visual tasks under head restraint. This has been essential for studies in macaques, enabling both accurate eye tracking and head stabilization for neurophysiology. In one set of experiments we compared the free viewing behavior of head-fixed marmosets to that of macaques, and found that their saccadic behavior is comparable across a number of saccade metrics and that saccades target similar regions of interest including faces. In a second set of experiments we applied behavioral conditioning techniques to determine whether the marmoset could control fixation for liquid reward. Two marmosets could fixate a central point and ignore peripheral flashing stimuli, as needed for receptive field mapping. Both marmosets also performed an orientation discrimination task, exhibiting a saturating psychometric function with reliable performance and shorter reaction times for easier discriminations. These data suggest that the marmoset is a viable model for studies of active vision and its underlying neural mechanisms.