Unfamiliar Pairs Research Articles

Kin recognition for incest avoidance in Damaraland mole-rats, Fukomys damarensis

Across taxa, breeding among close relatives is usually avoided because it incurs fitness costs to offspring. Incest is often averted through the dispersal of either sex from the natal area to breed. In some philopatric species, association among relatives extends into adulthood, and an ability to discriminate kin may be required for individuals to reduce inbreeding risk. Here, we aim to determine the mechanism of kin recognition for incest avoidance in the Damaraland mole-rat Fukomys damarensis , a cooperative breeder characterized by extreme reproductive skew. Pairs of opposite-sex adults were formed in the laboratory and, within pairs, genetic relatedness and degree of familiarity were manipulated through cross-fostering experiments. We found that unfamiliar pairs were more likely to engage in sexual behaviours and bred more successfully than familiar pairs, regardless of their genetic similarity. Females paired with unfamiliar males were also more likely to exhibit reproductive activation, characterized by increased levels of oestradiol and progesterone. This study shows that in Damaraland mole-rats, inbreeding avoidance can be achieved through a discrimination mechanism that relies on association during rearing, and that ovulation is induced by mating. This study advances our understanding of incest avoidance in species with constrained dispersal.

Effects of peer familiarity on Chinese English learners’ L2 learning in collaborative writing

AbstractIn second language education, the pairing of students for interaction, particularly based on peer familiarity, has garnered considerable attention from researchers. Despite this focus, studies examining the impact of peer familiarity on language learning during peer interactions have produced varied results, with limited exploration in the context of collaborative writing tasks. This study seeks to investigate the effects of peer familiarity on Chinese English learners’ language learning in collaborative writing. Two groups of participants were recruited, including five familiar pairs and five unfamiliar pairs. Their interactive dialogues throughout the collaborative writing process were recorded; transcribed; and then analyzed for the number, type, and outcome of language‐related episodes (LREs). Our findings revealed that the familiar pairs exhibited a significantly higher production of LREs and a greater success rate in solving these episodes compared to the unfamiliar pairs. Furthermore, all participants demonstrated a higher retention rate for successfully solved LREs compared to unsolved ones, although no significant difference was found between the two groups in terms of language learning retention. The findings offer pedagogical implications for student grouping in collaborative work.

Experience of a hierarchical relationship between a pair of mice specifically influences their affective empathy toward each other.

Prior experience of social hierarchy is known to modulate emotional contagion, a basic form of affective empathy. However, it is not known whether this behavioral effect occurs through changes in an individual's traits due to their experience of social hierarchy or specific social interrelationships between the individuals. Groups of four mice with an established in-group hierarchy were used to address this in conjunction with a tube test. The rank-1 and rank-4 mice were designated as the dominant or subordinate groups, respectively. The two individuals in between were designated as the intermediate groups, which were then used as the observers in observational fear learning (OFL) experiments, an assay for emotional contagion. The intermediate observers showed greater OFL responses to the dominant demonstrator than the subordinate demonstrators recruited from the same home-cage. When the demonstrators were strangers from different cages, the intermediate observers did not distinguish between dominant and subordinate, displaying the same level of OFL. In a reverse setting in which the intermediate group was used as the demonstrator, the subordinate observers showed higher OFL responses than the dominant observers, and this occurred only when the demonstrators were cagemates of the observers. Furthermore, the bigger the rank difference between a pair, the higher the OFL level that the observer displayed. Altogether, these results demonstrate that the hierarchical interrelationship established between a given pair of animals is critical for expressing emotional contagion between them rather than any potential changes in intrinsic traits due to the experience of dominant/subordinate hierarchy. PRACTITIONER POINTS: Subordinate observer or dominant demonstrator resulted in higher affective empathic response in familiar pairs but not unfamiliar pairs. The relative social rank of the observer with respect to the demonstrator had a negative linear correlation with the affective empathic response of the observer in familiar pairs but not unfamiliar pairs. The effect of social rank on affective empathy is attributed to the prior social hierarchical interrelationship between them and is not due to intrinsic attributes of an individual based on one's dominance rank.

Learning with friends and strangers: partner familiarity does not improve collaborative learning performance in younger and older adults

ABSTRACT Collaborative learning with a familiar partner can reduce age-related differences in learning and memory compared to learning alone. This study compares younger and older adults’ learning with familiar and unfamiliar partners to determine whether familiarity is beneficial for collaborative learning. Twenty-four younger adults aged 18–28 years and 24 older adults aged 60–80 years participated in familiar and unfamiliar pairs. Participants were asked to arrange abstract tangram shapes in a specific order on a grid over multiple trials; the directors’ tangram cards were arranged in a specific order on the grid and this order was communicated to the matcher. Older adults initially took longer to complete the task, using more words to correctly arrange the tangrams. Over multiple trials, a learning effect was observed in both groups, although older adults did not perform with similar efficiency to younger adults. Familiarity had no effect on performance. These findings suggest that the familiarity of a partner does not affect learning outcomes in younger or older adults when learning in a social context. Collaborative learning may be beneficial for older adults, even if they do not know their learning partner, which may have implications for adult education and lifelong learning.

Machine Learning Distinguishes Familiar from Unfamiliar Pairs of Subjects Performing an Eye Contact Task: A Systemic Physiology Augmented Functional Near-Infrared Spectroscopy Hyperscanning Study.

Eye contact is an important aspect of human communication and social interactions. Changes in brain and systemic physiological activity associated with interactions between humans can be measured with systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) hyperscanning, enabling inter-brain and inter-body synchronisation to be determined. In a previous study, we found that pairs of subjects that are socially connected show higher brain and body synchrony. To enable a deeper understanding, our aim was to build and automatically detect the best set of features to distinguish between two different groups (familiar and unfamiliar pairs). We defined several features based on the Spearman correlation and wavelet transform coherence (WTC) of biosignals measured on 23 pairs of subjects (13 familiar and 10 unfamiliar pairs) during eye contact for 10 min. Additional custom features that identify the maximum brain-to-body coupling instants between pairs were generated. After testing on combinations of different feature extraction methods, four subsets of features with the strongest discrimination power were taken into account to train a decision tree (DT) machine learning (ML) algorithm. We have obtained 95.65% classification accuracy using a leave-one-out cross-validation. The coupling features which represent the two maximum mean values resulting from the sum of 7 time-dependent WTC signals (oxyhaemoglobin concentration of the right prefrontal region, total haemoglobin concentration of the left and right prefrontal region, heart rate, electrodermal activity on the left and right wrist, and skin temperature on the right wrist) played an essential role in the classification accuracy. Training the DT-ML algorithm with combined brain and systemic physiology data provided higher accuracy than training it only with brain or systemic data alone. The results demonstrate the power of the SPA-fNIRS hyperscanning approach and the potential in applying ML to investigate the strength of social bonds in a wide range of social interaction contexts.

Mate fidelity improves survival and breeding propensity of a long-lived bird.

Evolutionary and behavioural ecologists have long been interested in factors shaping the variation in mating behaviour observed in nature. Although much of the research on this topic has focused on the consequences of mate choice and mate change on annual reproductive success, studies of a potential positive link between mate fidelity and adult demographic rates have been comparatively rare. This is particularly true for long-lived birds with multi-year, socially monogamous pair bonds. We used a 26-year capture-mark-recapture dataset of 3,330 black brent Branta bernicla nigricans to test whether breeding with a familiar mate improved future breeding propensity and survival. We predicted that experienced breeders nesting with a new partner would have rates of survival similar to familiar pairs because long-lived species avoid jeopardizing survival since their lifetime fitness is sensitive to this vital rate. In contrast, we expected that any costs of breeding with a new partner would be paid through skipping the subsequent breeding attempt. We found that unfamiliar pairs had lower subsequent breeding propensity than faithful partners. However, contrary to our expectations, individuals breeding with a new mate also suffered reduced survival. These results add to a small number of studies indicating that a positive relationship between mate retention and adult demographic rates may exist in a diverse array of avian species. Given these results, researchers should consider costs of mate change that extend beyond within-season reproductive success to fully understand the potential adaptive basis for perennial social monogamy. We caution that if mate retention enhances survival prospects, improvements in annual reproductive success with pair-bond length could be a secondary factor favouring perennial social monogamy, particularly in species with slower life-history strategies. Furthermore, some cases where annual reproductive success does not improve with pair-bond duration, yet multi-year pair bonds are common, could be explained by benefits afforded by mate fidelity to adult vital rates.

Convergence of physiological responses to pain during face-to-face interaction

Empathy with another’s pain is an important social glue for maintaining interpersonal relationships. In most previous studies investigating the sharing of pain, a signal conveying a painful experience is presented by a target (“sender”) as a stimulus to a participant (“receiver”), and the emotional/physiological responses of the participant are measured. However, this unilateral “sender-receiver” paradigm does not adequately address the possible bidirectional experience of shared pain accruing from interaction. Our aim was therefore to investigate the bidirectional effects of sharing pain in social settings. Thirty-six unfamiliar pairs were simultaneously and repeatedly exposed to the same pain-provoking (thermal) stimuli, either in a face-to-face or a “shielded” condition where a partition prevented the partner’s responses from being fully observed. We recorded the blood volume pulse of each participant to measure the acute sympathetic response while a pair of participants experienced the stimuli simultaneously. The results revealed that participants with weaker reactions elevated their physiological reactivity to the stimulus in accordance with their partner’s reactions in the face-to-face condition. The pair-level physiological similarity was also higher compared to the shielded condition. Such a low-to-high physiological convergence may underlie the collective elevation of pain expressions, which is often observed in interactive settings.

Number of Shoes Tested During a Running Shoe Mass Perception Task May Not Influence Accuracy

Commercially available running shoes differ in terms of their relative masses. It is unclear how well consumers may be able to judge mass differences from wearing alone, though previous studies suggest that perceptual outcomes may be influenced by experimental design factors such as the length of time worn. The purpose of this study was to investigate how the number of shoes used in a testing session impacts wearers' mass perceptual accuracy. Forty-eight young adult males ran for 5 min in 4 pairs of shoes (their own running shoes plus 3 unfamiliar pairs) before being asked whether an unfamiliar running shoe was heavier or lighter than their own, and to indicate perceptions of shoe heaviness (mass), comfort, stability, and temperature using visual analogue scales (VAS). A subset (n=18) was also asked to provide global rank orderings after wearing all 4 pairs of shoes. Participants were 67% accurate in the heavier/lighter task and 64% accurate in the global rank order task. Global rank order scores and VAS heaviness marks were significantly and positively correlated. Mass accuracy scores (n=48) were then compared to a previous study (n=25) performed by the same investigators using the same methods but with 6 pairs of shoes instead of 4. No difference in accuracy scores for either the heavier/lighter comparisons or global rank order scores between the study populations was found, suggesting that the number of test shoes may not influence mass perception accuracy.

Dominance-related contributions to collective territory defence are adjusted according to the threat

Across diverse societies, group members benefit from the cooperative maintenance of a shared territory (a public good). How such public goods are maintained has received extensive interest, yet individual contributions to cooperative territory defence remain poorly understood. Recent theory predicts that, in groups with social hierarchies, privileged individuals will contribute most to competition with rival groups as they benefit most from defence of the territory. Here, we investigated whether dominant individuals contribute more to territory defence in a group-territorial bird in which dominants monopolize within-group reproduction: the white-browed sparrow-weaver, Plocepasser mahali. Using simulated territorial intrusions, we demonstrate that dominants contributed significantly more than subordinates to territory defence. We also found that individual contributions were adjusted according to threat: males of both social classes significantly and similarly increased their contributions to defence in response to a high threat (playback of an unfamiliar pair's duet, rather than that of a neighbouring pair), which was associated with a stronger collective response by the group. Thus, while dominants contributed most as predicted by the asymmetry in benefits, subordinates did increase contributions when they were needed most (in small groups and under greater threat). Contributions by subordinates when needed most also highlights that dominants could still benefit substantially from tolerating the presence of subordinates despite their overall lower contributions. Our results show that public goods can be maintained despite unequal contributions and highlight the potential importance of context-dependent behavioural flexibility in mitigating collective action problems.

Effects of chronic intranasal oxytocin on behavior and cerebral glucose uptake in juvenile titi monkeys

Intranasal oxytocin (IN OXT) has been proposed as a treatment for autism spectrum disorder (ASD); however, little is known about the effects of long-term exposure. This is the first study in a non-human primate species to examine how developmental exposure to chronic IN OXT affects juvenile’s interactions with family members, social preference for parents versus strangers, anxiety-like behavior, and cerebral glucose metabolism. Titi monkeys are socially monogamous and biparental; their family bonds share important characteristics with human family bonds. Fourteen males and 15 females were treated intranasally with saline (n = 14) or 0.8 IU/kg OXT (n = 15), daily from 12 to 18 months of age. Compared to SAL-treated animals, OXT-treated animals of both sexes spent significantly more time grooming other family members (F1 = 8.97, p = 0.006). Overall, OXT-treated subjects were more social (F1 = 8.35, p = 0.005) during preference tests. OXT-treated females displayed an enhanced preference for their parents (t = 2.265, p = 0.026). OXT-treated males had a blunted preference for their parents and an increase in the time spent near unfamiliar pairs (F1 = 10.89, p = 0.001). During anxiety tests, OXT-treated males refused to complete the task more often than SAL-treated males and had longer latencies (p < 0.0001). Neuroimaging studies revealed that OXT-treated animals had higher glucose uptake across the social salience network as a whole after one month of treatment (F1,9 = 1.07, p = 0.042). Our results suggest moderate prosocial effects of chronic IN OXT, that did not depend on anxiolytic properties. We also found important sex differences that should be considered in a translational context.

Coping with strangers: how familiarity and active interactions shape group coordination in Corydoras aeneus.

Social groups composed of familiar individuals exhibit better coordination than unfamiliar groups; however, the ways familiarity contributes to coordination are poorly understood. Prior social experience probably allows individuals to learn the tendencies of familiar group-mates and respond accordingly. Without prior experience, individuals would benefit from strategies for enhancing coordination with unfamiliar others. We used a social catfish, Corydoras aeneus, that uses discrete, observable tactile interactions to assess whether active interactions could facilitate coordination, and how their role might be mediated by familiarity. We describe this previously understudied physical interaction, ‘nudges’, and show it to be associated with group coordination and cohesion. Furthermore, we investigated nudging and coordination in familiar/unfamiliar pairs. In all pairs, we found that nudging rates were higher during coordinated movements than when fish were together but not coordinating. We observed no familiarity-based difference in coordination or cohesion. Instead, unfamiliar pairs exhibited significantly higher nudging rates, suggesting that unfamiliar pairs may be able to compensate for unfamiliarity through increased nudging. By contrast, familiar individuals coordinated with comparatively little nudging. Second, we analysed nudging and cohesion within triplets of two familiar and one unfamiliar individual (where familiar individuals had a choice of partner). Although all individuals nudged at similar rates, the unfamiliar group-mate was less cohesive than its familiar group-mates and spent more time alone. Unfamiliar individuals that nudged their group-mates more frequently exhibited higher cohesion, indicating that nudging may facilitate cohesion for the unfamiliar group-mate. Overall, our results suggest that nudges can mitigate unfamiliarity, but that their usage is reduced in the case of familiar individuals, implying a cost is associated with the behaviour.

Familiarity and sex modulate size-dependent following behaviour in the Mediterranean killifish.

Living in a group offers the chance to follow the choices and the behaviours of other individuals. Following a group mate might confer fitness advantages if the group mate knows about resources such as food or shelters. Shoaling fish often follow larger group mates which, in most species, are generally older and therefore more experienced. Yet, the effect of individuals' characteristics other than size on following behaviour remains to be understood. For example, familiar fish and female shoals have been reported as more cohesive, which might be due to a differential tendency to follow in relation to familiarity and sex. Here, we investigated whether size, familiarity, sex, and the interaction between these factors affect fish following behaviour. We observed pairs of differently sized Mediterranean killifish, Aphanius fasciatus, exploring a new environment, and we recorded whether the rear fish followed the front fish when the latter changed swimming direction. In female and male pairs, and in unfamiliar pairs, smaller fish were more likely to follow the directional change of the larger fish than vice versa. In mixed-sex pairs and in familiar pairs, however, size did not affect following behaviour and larger fish followed as much as smaller fish did. Our results revealed that killifish's following decisions are determined by the size of the individuals, their level of familiarity, and their sex. These characteristics may have a notable impact on the behaviour of fish groups in nature.

Opportunities for female choice in the bed bug Cimex lectularius

AbstractBed bugs are cited as exemplars of sexual conflict because mating can only occur via traumatic insemination. However, past antagonistic coevolution between the sexes does not necessarily preclude current female choice. Here, we investigate opportunities for precopulatory female choice in bed bugs. We examined whether females seek out mating opportunities when they gain the most benefit: when females are virgin and/or have recently fed. But, we found that female mating and feeding status had little effect on female attraction to males and male odor. To determine whether females approach male harborages (home crevices) to seek matings in nature, we investigated where matings occurred among unfamiliar pairs of bed bugs. We found that, despite female attraction to male odor, matings were most likely to take place in the female's harborage rather than the male's harborage. We also examined the effect of feeding on male and female ability to mate. Whereas previous research reported that engorgement impaired female ability to refuse matings, we found that male feeding status had a larger effect on the success of mating encounters than female feeding status. Fed males had poor mating success, suggesting that males may be faced with a trade‐off between mating and feeding.

American lobsters, Homarus americanus, use vision for initial opponent evaluation and subsequent memory

Many animals, including crustaceans, engage in dominance fights and thus the risk of damage. This makes opponent assessment a critical component of social information gathering. American lobsters, Homarus americanus (H. Milne-Edwards, 1837), are well known for surprisingly complex social behavior. Males fight for dominance, and winners are preferred by females. Fighting success is correlated with body and claw size. To avoid injury, opponents assess each other before and during a fight. The loser later recognizes the winner based on urine odor and retreats early from subsequent fights. Most research has explored recognition in the context of chemical ecology. Here, we describe four experiments testing the largely unexplored visual communication of male lobsters. Two experiments address evaluation within unfamiliar pairs. The first shows that the visual image of a lobster's own reflection in a mirror enhances attacks on an unfamiliar conspecific odor plume. The second shows that increasing differences in crusher claw size between opponents cause gradually decreasing fight duration; this negative correlation is maintained when either vision or olfaction is blocked. Blocking either sense caused similar increases in fight duration. Two additional experiments tested visual memory of opponents. Blindfolding the loser of a first fight abolished the decrease in second-fight duration seen in control fights, similar to previous results based on blocking olfaction. Finally, painting the face (carapace around the eyes and rostrum) of the winner in a second fight did not prevent recognition by the loser. Together, these results demonstrate that vision makes contributions to lobster communication, specifically opponent evaluation.

House sparrows\u2019 (Passer domesticus) behaviour in a novel environment is modulated by social context and familiarity in a sex-specific manner

BackgroundExploratory behaviour is one of the best-investigated behavioural traits. However, little is known about how differences in familiarity, i.e. in the knowledge and previous experience with a companion can influence the exploration of a novel environment. However, to our knowledge, such a critical feature of the social environment has never been the target of a study relating it to exploratory behaviour in birds. Here we examined if familiarity with a conspecific could affect behavioural responses of individuals confronted with a novel environment. We recorded the latency to land on the ground, latency to feed, time spent feeding and number of sectors visited of 48 female and 48 male house sparrows (Passer domesticus) in an indoor aviary in three contexts: alone (individual context), with an unfamiliar and with a familiar same-sex companion.ResultsHouse sparrows landed sooner on the ground when in the familiar context than when in the individual context. Birds in unfamiliar pairs followed each other less than familiar birds, but this difference diminished with time spent exploring. Moreover, males and females differed in their behavioural responses in the unfamiliar context. Females with a familiar companion landed sooner than when they were paired with an unfamiliar conspecific, whereas only the presence of a companion but not familiarity reduced males latency to land on the ground. Finally, when considering the unfamiliar context males had shorter latencies to forage and thus spent more time eating than females.ConclusionsThe presence or absence of a companion and its familiarity with the focal individual influenced differently the behavioural responses of male and female house sparrows in a novel environment. As house sparrows are strongly sociable, the influence of the social environment is likely to be of paramount importance to understand the selective pressures acting on them, particularly in recently colonized areas with ephemeral food sources. Our results shed light on the complex influence that the social environment has on the behavioural responses of a cosmopolitan bird.

Sex composition modulates the effects of familiarity in new environment

In many social species, when an individual is associated with familiar conspecifics, it displays an array of behaviours that may confer benefits (e.g., increased boldness and faster habituation to novel environments). In fish, these effects of familiarity have been studied using individuals of only one sex or juveniles. Since shoals often vary regarding sex composition and males and females show different social behaviours, we hypothesised that social familiarity’s effects vary with group sex composition. We tested this hypothesis by comparing the exploratory behaviour of groups of two females, two males, and one male and one female Mediterranean killifish, Aphanius fasciatus, which were either familiar or unfamiliar. Pairs of familiar females were bolder than pairs of unfamiliar females, whereas males showed the opposite trend. Pairs of familiar females also showed faster habituation to the novel environment and, at the beginning of the test, were more cohesive compared to pairs of unfamiliar females. Pairs of familiar mixed-sex fish habituated faster to the novel environment than unfamiliar pairs. Pairs of familiar males did not show any beneficial effect of familiarity relative to pairs of unfamiliar males. Hence, the effects of social familiarity on exploratory behaviour, and likely the associated benefits, appear to depend on the sex composition of the pair in the Mediterranean killifish.

The modulatory effect of semantic familiarity on the audiovisual integration of face-name pairs.

To recognize individuals, the brain often integrates audiovisual information from familiar or unfamiliar faces, voices, and auditory names. To date, the effects of the semantic familiarity of stimuli on audiovisual integration remain unknown. In this functional magnetic resonance imaging (fMRI) study, we used familiar/unfamiliar facial images, auditory names, and audiovisual face-name pairs as stimuli to determine the influence of semantic familiarity on audiovisual integration. First, we performed a general linear model analysis using fMRI data and found that audiovisual integration occurred for familiar congruent and unfamiliar face-name pairs but not for familiar incongruent pairs. Second, we decoded the familiarity categories of the stimuli (familiar vs. unfamiliar) from the fMRI data and calculated the reproducibility indices of the brain patterns that corresponded to familiar and unfamiliar stimuli. The decoding accuracy rate was significantly higher for familiar congruent versus unfamiliar face-name pairs (83.2%) than for familiar versus unfamiliar faces (63.9%) and for familiar versus unfamiliar names (60.4%). This increase in decoding accuracy was not observed for familiar incongruent versus unfamiliar pairs. Furthermore, compared with the brain patterns associated with facial images or auditory names, the reproducibility index was significantly improved for the brain patterns of familiar congruent face-name pairs but not those of familiar incongruent or unfamiliar pairs. Our results indicate the modulatory effect that semantic familiarity has on audiovisual integration. Specifically, neural representations were enhanced for familiar congruent face-name pairs compared with visual-only faces and auditory-only names, whereas this enhancement effect was not observed for familiar incongruent or unfamiliar pairs. Hum Brain Mapp 37:4333-4348, 2016. © 2016 Wiley Periodicals, Inc.

The effect of propensity to trust and familiarity on perceptions of trustworthiness over time

Research on trust has burgeoned in the last two decades. Despite the growing interest in trust, little is known about the differences in trust between familiar and unfamiliar interactions. The current empirical study explored propensity to trust as predictors of trustworthiness over time in familiar and unfamiliar dyads. Utilizing latent growth modeling we found propensity to trust was related to initial perceptions of trustworthiness in unfamiliar pairs but not in familiar pairs. In addition, familiarity was related to initial perceptions of trustworthiness, but familiarity only influenced the change in integrity. However, there were significant differences in change variances between familiar and unfamiliar pairs. Implications of the findings are also discussed.

Exploring Synchronicity in the Heart Rates of Familiar and Unfamiliar Pairs of Horses and Humans Undertaking an In-Hand Task

ABSTRACTPhysiological responses that occur in horses and humans during their interactions, on the ground and during ridden work, have been investigated in a number of studies with some conflicting results. These suggest that in some situations emotional state may be transferred from humans to horses and that there is the potential for the heart rates of horse–human pairs to become synchronized during ridden work. Here we explore the effect of familiarity on the physiological responses of horse–human pairs completing a task in-hand, using heart rate as an indicator for emotional state. We investigated differences in heart rate response between familiar and unfamiliar pairings and the possibility of heart rate synchronization within each pair. Complete sets of horse and human heart rate data were available for 17 horses. We found a significant order affect, with higher horse heart rates seen the first time around the course regardless of whether a familiar or unfamiliar handler was leading (Wilcoxon test: Z=–2.67, p<0.05). However, despite this, the horses’ mean heart rates for each course were significantly higher with the unfamiliar handler than with the familiar handler (Wilcoxon test: Z=–4.46, p<0.001). In contrast, human heart rates were higher when paired with a familiar horse compared with an unfamiliar horse (Mann-Whitney U test: Z=–5.08, p<0.001). Significant correlations between horse and human heart rates were seen in three familiar pairings and two unfamiliar pairings. Our findings indicate that the relationship between horse and human heart rates during interactions is not straightforward or consistent between horses and humans, and is likely to depend on a number of factors such as experience of the test situation. Although the lower heart rates seen in horses being led by their familiar handler suggest that they are more relaxed with someone they know, this could not be said for the human partner.

Bodystorming: effects of collaboration and familiarity on improvising contemporary dance.

In contemporary dance, cognitive events are not necessarily restricted "to the skin or skull of an individual" (Hutchins in Int Encycl Soc Behav Sci 2068-2072, 2001) but distributed across dancers during collaborative improvisation. There is some experimental evidence of greater output when people perform problem-solving tasks alone. However, when a task is challenging and paired participants are familiar with each other, pairwise and emergent outcomes are more plentiful than solo outcomes. We investigate these factors in the context of dance with the broad hypothesis that innovation is enhanced when dancers improvise together compared with when they improvise alone. Dancers (N = 10) in a professional company improvised for 2 min alone and then with another dancer. Dancer familiarity (familiar, unfamiliar) and task (expressive, non-expressive) were crossed (within-subjects). The improvisations were video-recorded over 2 h in the dancers' usual improvisation space. After each improvisation, the dancers: stated the number of movement ideas expressed and rated task ease, satisfaction, interest, novelty, originality and clarity. In both tasks, there was a tendency for self-report of a greater number of movement ideas expressed in familiar and unfamiliar pairs than alone. Ratings of task ease, satisfaction, interest, clarity, etc. were slightly higher in the unfamiliar pair condition. In the non-expressive task, ratings of the task were higher in pairs (M = 3.02, SD 0.82) than in the solo (M = 2.67, SD 0.96) condition. Distributed creativity, relational cognition and social facilitation are used to interpret the results.