Unfamiliar Individuals Research Articles

Multimodal First Impression Analysis with Deep Residual Networks

People form first impressions about the personalities of unfamiliar individuals even after very brief interactions with them. In this study we present and evaluate several models that mimic this automatic social behavior. Specifically, we present several models trained on a large dataset of short YouTube video blog posts for predicting apparent Big Five personality traits of people and whether they seem suitable to be recommended to a job interview. Along with presenting our audiovisual approach and results that won the third place in the ChaLearn First Impressions Challenge, we investigate modeling in different modalities including audio only, visual only, language only, audiovisual, and combination of audiovisual and language. Our results demonstrate that the best performance could be obtained using a fusion of all data modalities. Finally, in order to promote explainability in machine learning and to provide an example for the upcoming ChaLearn challenges, we present a simple approach for explaining the predictions for job interview recommendations.

Brain size does not impact shoaling dynamics in unfamiliar groups of guppies (Poecilia reticulata)

Collective movement is achieved when individuals adopt local rules to interact with their neighbours. How the brain processes information about neighbours’ positions and movements may affect how individuals interact in groups. As brain size can determine such information processing it should impact collective animal movement. Here we investigate whether brain size affects the structure and organisation of newly forming fish shoals by quantifying the collective movement of guppies (Poecilia reticulata) from large- and small-brained selection lines, with known differences in learning and memory. We used automated tracking software to determine shoaling behaviour of single-sex groups of eight or two fish and found no evidence that brain size affected the speed, group size, or spatial and directional organisation of fish shoals. Our results suggest that brain size does not play an important role in how fish interact with each other in these types of moving groups of unfamiliar individuals. Based on these results, we propose that shoal dynamics are likely to be governed by relatively basic cognitive processes that do not differ in these brain size selected lines of guppies.

The effects of familiarity on escape responses in the Trinidadian guppy (Poecilia reticulata).

Predation is the main cause of mortality during early life stages. The ability to avoid and evade potential threats is, therefore, favoured to evolve during the early stages of life. It is also during these early stages that the process of familiarization occurs. It has long been recognized that associating with familiar individuals confers antipredator benefits. Yet gaps in our knowledge remain about how predator evasion is affected by social experience during early stages. In this study, we test the hypothesis that familiarization acquired during early life stages improves escape responses. Using the guppy Poecilia reticulata, we examine the effect of different recent social conditions in the three main components of predator evasion. Using high-speed motion analysis, we compared the number of individuals in each test group that responded to a visual stimulus, their reactive distance and magnitude of their response (maximum speed, maximum acceleration and distance) in groups composed either of familiar or non-familiar individuals. Contrary to the prediction, groups composed of familiar individuals were less responsive than groups of unfamiliar individuals. Reactive distance and magnitude of response were more dependent on individual size rather than on familiarity. Larger individuals reached higher maximum speeds and total distances in their escape response. Our result indicates that familiarity is likely to affect behaviour earlier in a predator-prey interaction, which then affects the behavioural component of the response. Taken together, our study contributes to previous ones by distinguishing which components of an escape response are modulated by familiarity.

Estimation of genetic parameters for lesion scores and growth traits in group-housed pigs.

Pigs housed in groups are remixed with unfamiliar individuals, which can trigger aggressive interactions, potentially compromising animal welfare. Skin lesions are a reliable indicator trait of aggression and are moderately heritable, suggesting that aggression may be reduced through selection. This study estimated genetic parameters of skin lesions of pigs at multiple life stages, explored genetic correlations of skin lesions between age groups and body location, and studied the relationship between skin lesions and production traits of commercial importance. A population of 1,079 Yorkshire pigs was strategically remixed into new groups of familiar and unfamiliar animals at 3 life stages (weaning, grow-finish, and mature gilts). Skin lesions (fresh, bright red cuts) were counted immediately prior to mixing and 24 h and 3 wk after mixing across 3 body regions: anterior, central, and caudal. Weights were recorded prior to each mixing event. Prior to slaughter, backfat thickness and loin muscle area were determined using ultrasound. Univariate analyses were performed to obtain heritability estimates of lesion scores. Bivariate analyses were performed with response variables being skin lesions, weight gain per life stage, backfat thickness, or loin muscle area, depending on the relationship of interest, to obtain correlations. Lesion score heritabilities ranged from 0.10 to 0.40 and were significant ( < 0.05). Heritability was highest for lesions on the anterior region of the body for 24 h and 3 wk after mixing. Lesions to the central and caudal areas showed the highest genetic correlation at each stage of production, whereas those to the anterior and caudal regions had the lowest correlation. The highest genetic correlation was found between the mature gilt and grow-finish stages, whereas the weaning and mature gilt stages had the lowest correlations. Genetic correlations between lesions and production traits were not significantly different from 0 for weight gain and backfat thickness, but loin muscle area was negatively correlated with lesions ( = 1.17 × 10, = 2.30 × 10, and = 6.08 × 10 for anterior, central, and caudal lesions, respectively). These results are promising for the industry because they suggest that pigs selected for reduced lesions will show increased loin muscle area without negative effects on growth. Alternatively, selection for these production traits would not increase lesions.

Chronic central oxytocin infusion impairs sociability in mandarin voles

Oxytocin (OT) has been reported to increase social contact, however some studies have related OT to reduced social contact, particularly with unfamiliar individuals. The underlying mechanisms of OT on social contact remain unclear. In this study, male mandarin vole (Microtus mandarinus), a socially monogamous rodent, was used as an animal model in which osmotic minipumps were used to intracerebroventricularly administer two dosages of OT or saline for 12 consecutive days. We examined the effect of long-term OT treatment on social behavior, anxiety levels, and levels of oxytocin, vasopressin (AVP) and dopamine (DA) receptors mRNA expression in the nucleus accumbens (NAcc), and medial amygdala (MeA). The data showed that chronic central OT infusion decreased social preference behavior (a reduction of preference for interacting with novel social stimulus relative to a novel object) concomitant to a reduction of OT receptors in the NAcc and MeA. We also found alterations in AVP and DA receptor levels in the NAcc and MeA after treatment with OT. Moreover, chronic central OT treatment did not affect levels of anxiety-related behavior in male voles. In conclusion, these results indicated that chronic OT treatment may differ from the treatment effects predicted in short-term studies, and significant dosage effects were observed.

Social security: social relationship strength and connectedness influence how marmots respond to alarm calls

Individuals vary in the number and types of social relationships they maintain. If beneficial, social relationships may reduce predation risk and thus increase an individual’s sense of security. We tested this hypothesis by studying the responses of female yellow-bellied marmots (Marmota flaviventer) to broadcast alarm calls from unfamiliar individuals. First, we quantified affiliative interactions of animals in the field to calculate a set of social network measures. Because attributes of sociality are often correlated, we used principal component analysis to reduce our social network metrics to two unrelated factors and used the social network measure that accounted for the most variance for each principal component in further analyses. We then quantified the change in time allocated to vigilance and foraging following alarm call playback from baseline levels to the first 30 s and the second 30 s period (i.e., 31–60 s) following playback. We expected that if marmots with strong affiliative relationships felt more secure, they would forage more and allocate less time to vigilance after their immediate vigilance response to the broadcast alarm calls. Using mixed effects models that controlled for variation explained by a number of biologically important covariates and permutation tests to test the significance of social network variables, we found that marmots with a higher incloseness allocated significantly more time to vigilance in both the first and second 30 s after hearing a novel alarm call. Additionally, and while not significant (the observed parameter estimate fell between the 90 and 95% CI), marmots with a higher outstrength increased foraging in the second 30 s after hearing a novel alarm call. If we assume that time allocated to foraging is a measure of security, then marmots with strong affiliative relationships reacted more to an alarm call from a novel individual and seemingly felt more secure than their counterparts. Our results, therefore, suggest that strong social relationships increase perceptions of security and illustrate an effect of social relationships on predation risk assessment. In many species, including humans, there are benefits from maintaining good social relationships. These benefits include better health and greater longevity. We studied yellow-bellied marmots, a ground-dwelling squirrel that is notable because it has variable social relationships. Capitalizing on this social variation, we found that marmots that maintain strong affiliative relationships with other marmots may indeed forage more after hearing an artificially broadcast alarm call than marmots with weaker affiliative relationships. This result suggests that marmots that are more socially connected with others in their group may feel relatively more secure, possibly because they have others that can help them assess risk, and that a benefit of maintaining strong friendly social ties is that it permits animals to forage more. Thus, we suggest a new way that social relationships can be beneficial: they increase perceptions of security and this ultimately may facilitate foraging.

Familiarity dominates relatedness in mate selection in ladybirds

AbstractCuticular and volatile hydrocarbons have been known to act as signatures of sex, species, mating partners and relatives in ladybird beetles. Our aim was to see (1) whether chemical proximity to an individual establishes familiarity and whether this modulates behaviour, and (2) whether ladybirds can detect familiarity or relatedness, and if so, which quality they respond to more favourably. The first experiment investigated whether familiarity can be established in Cheilomenes sexmaculata on the basis of perception of volatile profiles, and the second experiment investigated whether familiarity is stronger than relatedness in determining mate preference. Males and females were housed in an arena which permitted only chemical contact, for 1–10 days, to create familiarity. Females were then given a choice of familiar versus unfamiliar males and were found to preferentially mate with unfamiliar males. The preference for unfamiliar males increased with confinement duration. This preference was also evident in mating as well as in reproductive performance: females mated faster with unfamiliar males and males remained in copula for longer duration with novel females, and higher number of eggs was also laid by females that mated with unfamiliar males. In the second experiment, females were given a choice of related unfamiliar and unrelated familiar males and they preferred the latter, indicating that relatives were not preferred even when they were unfamiliar. When choosing between relatives and familiar individuals, the aversion to relatives was stronger than the affinity for unfamiliar individuals. Bias against mating with relatives is probably a function to prevent inbreeding depression.

Familiarity affects collective motion in shoals of guppies ( Poecilia reticulata )

The coordinated and synchronized movement of animals in groups often referred to as collective motion emerges through the interactions between individual animals within the group. Factors which affect these interactions have the potential to shape collective movement. One such factor is familiarity, or the tendency to bias behaviour towards individuals as a result of social recognition. We examined the effect of familiarity on the expression of collective motion in small shoals of female guppies (Poecilia reticulata). Groups comprising familiar individuals were more strongly polarized than groups of unfamiliar individuals, particularly when in novel surroundings. The ability to form more strongly polarized shoals potentially promotes information transfer and enhances the anti-predator benefits of grouping.

How methamphetamine exposure during different neurodevelopmental stages affects social behavior of adult rats?

Social behavior involves complex of different forms of interactions between individuals that is essential for healthy mental and physical development throughout lifespan. Psychostimulants, including methamphetamine (MA), have neurotoxic effect, especially, if they are targeting CNS during its critical periods of development. The present study was aimed on evaluation of changes in social interactions (SI) following scheduled prenatal/neonatal MA treatment in combination with acute application in adulthood. Eight groups of male and eight groups of female rats were tested in adulthood: rats, whose mothers were exposed to MA (5mg/ml/kg) or saline (SA, 1ml/kg) during the first half of gestation (ED 1–11), the second half of gestation (ED 12–22) and neonatal period (PD 1–11). To do this, we compared indirect neonatal applications via the exposed dams with group of rat pups that received MA or SA directly through injections. In adulthood, half animals from each group were injected with MA (1mg/kg), second half with saline 45min prior to the Social Interaction Test. Females and males were observed for social and nonsocial activities of two unfamiliar individuals of the same sex and treatment in a familiar Open field arena. The present study demonstrated that prenatal/neonatal MA exposure leads to decrease the time spent in genital investigation, following and nonsocial activity. Acute dose of MA leads to a decrease in all SI patterns and to an increase in nonsocial activities relative to acute SA. Females were more active than males. Animals exposed to prenatal/neonatal treatment during the second half of gestation (ED 12–22) and throughout lactation period (PD 1–11 indirect/direct) had fewer SI and greater exploratory behavior than animals exposed during the first half of gestation (ED 1–11).

Superb fairy-wrens respond more to alarm calls from mate and kin compared to unrelated individuals

Lay SummaryIndividual discrimination can influence social behaviors. Here, we show that superb fairy-wrens (Malurus cyaneus), a cooperative bird species, have individually distinct mobbing alarm calls and that receivers discriminated between 2 unfamiliar individuals using mobbing alarm calls alone. Superb fairy-wrens also responded differently to playback of calls from their mate and kin versus individuals from another population.

Social relationships enhance the time spent eating and intake of a novel diet in pregnant Hanwoo (Bos taurus coreanae) heifers.

The objective of this study was to evaluate the effects of social relationships on the feed intake, eating behavior, and growth, upon exposure to a novel diet, in Hanwoo (Bos taurus coreanae) heifers during pregnancy. Twenty-four pregnant Hanwoo heifers, averaging 438 ± 27.8 kg in weight, 21 months in age, and 194 ± 8.5 days in pregnancy, were involved in a two-month (eight weeks) experiment. The heifers were randomly assigned to either the single housing group (SG; one individual per pen, n = 12), or the paired housing group (PG; two individuals per pen, n = 12). All pens were of the same size (5 × 5 m) and provided with one feed bin, which automatically recorded the individual feed intake and eating behavior. As the experiment began, the diet of the heifers was switched from a total mixed ration (TMR; 250 g/kg ryegrass straw and 750 g/kg concentrate mix) to a forage-only diet (mixed hay cubes composed of 500 g/kg alfalfa, 250 g/kg timothy, and 250 g/kg blue grass hay). The heifers were fed ad libitum twice a day. The individual feed intake and eating behavior were recorded daily throughout the experiment, and body weights (BWs) were measured every four weeks before the morning feeding. PG animals visited the feed bin 22% less often than SG. PG, however, stayed 39% longer in the feed bin and consumed 40% more feed per visit, compared with SG. Consequently, PG heifers spent 23% more time in eating and had 16% more daily dry matter intake than SG during the experiment. Average daily gain during the experimental period tended to be greater in PG than in SG. When pregnant Hanwoo heifers encountered a novel diet, social relationships (i.e., presence of a pen-mate) enhanced their time spent eating and feed intake. Social interactions, even with an unfamiliar individual, may be helpful for pregnant Hanwoo heifers cope with a diet challenge compared to solitary situation.

Investigating the cognitive structure of stereotypes: Generic beliefs about groups predict social judgments better than statistical beliefs.

Stereotypes are typically defined as beliefs about groups, but this definition is underspecified. Beliefs about groups can be generic or statistical. Generic beliefs attribute features to entire groups (e.g., men are strong), whereas statistical beliefs encode the perceived prevalence of features (e.g., how common it is for men to be strong). In the present research, we sought to determine which beliefs-generic or statistical-are more central to the cognitive structure of stereotypes. Specifically, we tested whether generic or statistical beliefs are more influential in people's social judgments, on the assumption that greater functional importance indicates greater centrality in stereotype structure. Relative to statistical beliefs, generic beliefs about social groups were significantly stronger predictors of expectations (Studies 1-3) and explanations (Study 4) for unfamiliar individuals' traits. In addition, consistent with prior evidence that generic beliefs are cognitively simpler than statistical beliefs, generic beliefs were particularly predictive of social judgments for participants with more intuitive (vs. analytic) cognitive styles and for participants higher (vs. lower) in authoritarianism, who tend to view outgroups in simplistic, all-or-none terms. The present studies suggest that generic beliefs about groups are more central than statistical beliefs to the cognitive structure of stereotypes. (PsycINFO Database Record

The Utility of Multiple Synthesized Views in the Recognition of Unfamiliar Faces

ABSTRACTThe ability to recognize an unfamiliar individual on the basis of prior exposure to a photograph is notoriously poor and prone to errors, but recognition accuracy is improved when multiple photographs are available. In applied situations, when only limited real images are available (e.g., from a mugshot or CCTV image), the generation of new images might provide a technological prosthesis for otherwise fallible human recognition. We report two experiments examining the effects of providing computer-generated additional views of a target face. In Experiment 1, provision of computer-generated views supported better target face recognition than exposure to the target image alone and equivalent performance to that for exposure of multiple photograph views. Experiment 2 replicated the advantage of providing generated views, but also indicated an advantage for multiple viewings of the single target photograph. These results strengthen the claim that identifying a target face can be improved by providing multiple synthesized views based on a single target image. In addition, our results suggest that the degree of advantage provided by synthesized views may be affected by the quality of synthesized material.

Can common cuckoos discriminate between neighbours and strangers by their calls?

Common cuckoos, Cuculus canorus, are brood parasites: they lay their eggs in the nests of other bird species, and let these hosts incubate their eggs and feed and rear the nestlings. Although cuckoos do not show parental care, they demonstrate complex social interactions, including territorial behaviours and male–male aggression. Cuckoos have a well-known and simple two-phrase call (‘cu’ and ‘coo’), uttered by males during their breeding season. Previous studies suggested that the ‘cu-coo’ call of males is individually unique, potentially allowing discrimination between different classes of males. Using playback experiments in a dense population of radiotagged cuckoos, we tested whether neighbouring males are tolerated more than unfamiliar intruders: the classic ‘dear enemy’ phenomenon. Focal birds responded more aggressively to the calls of unfamiliar simulated intruders (strangers) than to the calls of conspecifics with whom they shared territorial boundaries (familiar neighbours). Cuckoos responded quickly, within, on average, less than half a minute; they often approached the loudspeaker to within 5–10 m, even from up to 80 m away, and used their ‘cu-coo’ calls in response. Our results showed that cuckoos used their simple call for the discrimination of familiar versus unfamiliar individuals, and did so specifically to defend their own territories. In turn, cuckoos showed tolerance to nearby conspecifics, for example neighbours with overlapping territories, and did not respond to control playbacks. Finally, as typically more than one cuckoo was interested in the playbacks, this study confirmed the opportunity for brood-parasitic birds to socialize during the breeding season.

Perception of emotional valence in horse whinnies

BackgroundNon-human animals often produce different types of vocalisations in negative and positive contexts (i.e. different valence), similar to humans, in which crying is associated with negative emotions and laughter is associated with positive ones. However, some types of vocalisations (e.g. contact calls, human speech) can be produced in both negative and positive contexts, and changes in valence are only accompanied by slight structural differences. Although such acoustically graded signals associated with opposite valence have been highlighted in some species, it is not known if conspecifics discriminate them, and if contagion of emotional valence occurs as a result. We tested whether domestic horses perceive, and are affected by, the emotional valence of whinnies produced by both familiar and unfamiliar conspecifics. We measured physiological and behavioural reactions to whinnies recorded during emotionally negative (social separation) and positive (social reunion) situations.ResultsWe show that horses perceive acoustic cues to both valence and familiarity present in whinnies. They reacted differently (respiration rate, head movements, height of the head and latency to respond) to separation and reunion whinnies when produced by familiar, but not unfamiliar individuals. They were also more emotionally aroused (shorter inter-pulse intervals and higher locomotion) when hearing unfamiliar compared to familiar whinnies. In addition, the acoustic parameters of separation and reunion whinnies affected the physiology and behaviour of conspecifics in a continuous way. However, we did not find clear evidence for contagion of emotional valence.ConclusionsHorses are thus able to perceive changes linked to emotional valence within a given vocalisation type, similar to perception of affective prosody in humans. Whinnies produced in either separation or reunion situations seem to constitute acoustically graded variants with distinct functions, enabling horses to increase their apparent vocal repertoire size.

The effects of contextual familiarity on alcohol expectancies.

Social familiarity has been widely studied by researchers across a range of psychological disciplines, with level of familiarity in social context being indicated as a powerful factor influencing affective and motivational states. The degree of familiarity among drinking companions has further been linked to patterns of alcohol use, with regular drinking in unfamiliar social settings being associated with heavy consumption and drinking in highly familiar settings being indicated as a potentially protective factor. But social familiarity has received relatively little attention in relation to the psychological and cognitive processes supporting alcohol consumption. Here, in 2 studies, we explore the effects of social familiarity as it relates to alcohol expectancies-psychological processes believed to serve as among the most proximal determinants of alcohol consumption. In Study 1, we use a between-subjects design to explore the effects of familiarity in a sample of 400 undergraduates (40% male), producing evidence that individuals believe that alcohol consumption will be associated with significantly greater social enhancement and tension reduction when it is consumed in the company of unfamiliar versus familiar individuals. In Study 2 (N = 107; 41% male), we replicate these effects using a within-subject design and reveal effects of familiarity that are large in magnitude. Results of these studies provide initial evidence for familiarity among drinking companions as a factor driving beliefs surrounding alcohol's effects, and indicate familiarity as a potentially promising line of inquiry for future research exploring determinants of drinking. (PsycINFO Database Record

Social spatial cognition in rat tetrads: how they select their partners and their gathering places.

Spatial organization is an extensively studied field, in which most of the research has been on how the physical environment is perceived and conceived. There is a consensus that physical attributes such as environment geometry and landmarks are key factors in shaping spatial cognition. Nevertheless, the numerous studies of spatial behavior have usually been carried out on individuals, thereby overlooking the possible impact of the social environment. In the present study, rats were exposed to an unfamiliar open-field, first alone and then in tetrads of unfamiliar individuals, in order to monitor and analyze when and how their individual spatial behavior converged to a group spatial behavior. We found that the unfamiliar rats spent most of their time in companionship, first with preferred partners and ultimately as a quartet. Specifically, group formation was dynamic and gradual, with the rats first forming duos, then trios, and ultimately a quartet. Trios and quartets mostly huddled in the same specific corner that became a shared home base, from which they took solo or duo roundtrips to the arena. The present study unveils how, by means of gradual interactions among self, place, and conspecifics, four unfamiliar rats organized together their social spatial behavior.

Territorial olive frogs display lower aggression towards neighbours than strangers based on individual vocal signatures

Some territorial animals display a form of social recognition in which they direct low levels of aggression towards established neighbours, but maintain greater readiness to respond aggressively towards unfamiliar individuals. In many taxa, such as songbirds, this so-called ‘dear enemy’ effect involves discrimination between neighbours and strangers based on individually distinctive vocal signatures. Although most anuran amphibians (frogs and toads) are highly vocal, and many are also territorial, we know very little about neighbour–stranger discrimination in this group. In the present study of the olive frog, Babina adenopleura (Ranidae), we show that the vocal signals of males are individually distinct, and that territory holders use this information to direct lower levels of aggression towards their nearby neighbours. Analyses of individual variation in advertisement calls revealed many individually distinctive spectral and temporal acoustic properties, with spectral properties contributing most towards statistical discrimination among individuals. In a field playback experiment that simulated territorial intrusions, territorial males had higher thresholds for producing aggressive calls in response to the advertisement calls of their nearby neighbours compared with those of strangers. A simple model based on sound attenuation due to spherical spreading estimated that males responded aggressively to strangers at distances that were approximately twice as far away as for neighbours and that were similar to intermale distances recorded in the field. Together, results from this study indicate that territorial male olive frogs develop vocally mediated dear enemy relationships with their nearby neighbours. These results highlight the potential for convergence in social recognition systems across diverse taxa.

Macaques attend to scratching in others

Self-directed behaviours in primates as a response to increasing psychological or physiological stress are a well-studied phenomenon. There is some evidence that these behaviours can be contagious when observed by conspecifics, but the adaptive function of this process is unclear. The ability to perceive stress in others and respond to it could be an important part of sustaining cohesiveness in social primates, but spontaneously acquiring stress-related behaviours (and potentially emotional states) from all group mates via contagion could be maladaptive. To investigate this, a group of captive Barbary macaques, Macaca sylvanus, were presented with videos of conspecifics engaging in self-directed behaviour (scratching) and neutral behaviour. Behavioural responses as a result of exposure to the stimuli were compared (1) between familiar and unfamiliar individuals, and (2) within familiar individuals to consider the modulating effects of social relationships. Our results did not show contagious scratching in this species. However, there were differences in how individuals attended to the scratching stimuli. Subjects were more attentive to scratching videos than to neutral videos and familiar than unfamiliar individuals. Within the familiar individuals, subjects were more attentive to those to whom they were weakly bonded. We suggest that increased attention to scratching behaviours may be adaptive in order to monitor and avoid stressed group mates, whose subsequent behaviour may be unpredictable and aggressive. Monitoring group mates who are not allies may also be adaptive as they may pose the biggest risk. These findings will help increase our understanding of subtle cues that can be communicative in primates, and also the evolutionary steps towards understanding others.

Capuchins recognize familiar faces

Although growing neural evidence suggests that human and nonhuman primates share a similar face-processing mechanism, evidence from behavioural research has been mixed. If primates share a similar face-processing system, one would expect to observe similar behavioural effects in both human and nonhuman primates. A particularly robust effect observed in humans is the familiarity effect; humans are better able to recognize familiar as opposed to unfamiliar individuals. Here, we used a matching-to-sample paradigm to examine capuchin monkeys' ability to discriminate conspecific faces across three degrees of familiarity: individuals living in one's own social group (‘in-group’), individuals living in one's neighbouring group (‘out-group’) and completely unfamiliar individuals (‘unfamiliar’). We hypothesized that if capuchins utilize their knowledge of familiar individuals to help them discriminate photos of conspecific faces, then performance on the recognition task would increase with the familiarity of the individual. Capuchins were better able to individuate familiar in-group members and familiar out-group members compared to unfamiliar individuals, suggesting that familiarity affects capuchins' ability to discriminate conspecific faces, as it does that of humans and apes. However, there was no significant difference between in-group members and out-group members, suggesting that the concept of ‘familiarity’ may extend to individuals living in neighbouring groups that one interacts with regularly. This would be a fitness advantage for social species, like capuchins, which compete with neighbouring groups over access to food and mates. It may be an advantage for males in particular as they emigrate to neighbouring groups when they reach maturity.