Emotional contagion is suggested to facilitate group life by enhancing synchronized responses to the environment. Cooperative breeders are an example of a social system that requires such intricate coordination between individuals. Therefore, we studied emotional contagion in common marmosets by means of a judgement bias test. Demonstrators were exposed to an emotion manipulation (i.e., positive, negative, control), and observers perceived only the demonstrator's behaviour. We predicted that the positive or negative states of the demonstrator would induce matching states in the observer, indicating emotional contagion. All subjects' emotional states were assessed through behaviour and cognition, the latter by means of a judgement bias test. Behavioural results showed a successful emotion manipulation of demonstrators, with manipulation-congruent expressions (i.e., positive calls in the positive condition, and negative calls and pilo-erect tail in the negative condition). Observers showed no manipulation-congruent expressions, but showed more scratching and arousal after the positive manipulation. Concerning the judgement bias test, we predicted that subjects in a positive state should increase their response to ambiguous cues (i.e., optimism bias), and subjects in a negative state should decrease their response (i.e., pessimism bias). This prediction was not supported as neither demonstrators nor observers showed such bias in either manipulation. Yet, demonstrators showed an increased response to the near-positive cue, and additional analyses showed unexpected responses to the reference cues, as well as a researcher identity effect. We discuss all results combined, including recently raised validation concerns of the judgement bias test, and inherent challenges to empirically studying emotional contagion.

Bristol Veterinary School Langford House University of Bristol Bristol UK

Department of Behavioral and Cognitive Biology Faculty of Life Sciences University of Vienna Vienna Austria

Department of Zoology University of South Bohemia Budweiss Czech Republic

Division of Livestock Sciences Department of Sustainable Agricultural Systems University of Natural Resources and Life Sciences Vienna Austria

Evolutionary Cognition Group Department of Anthropology University of Zürich Zürich Switzerland

Social Cognitive and Affective Neuroscience Unit Department of Cognition Emotion and Methods in Psychology Faculty of Psychology University of Vienna Vienna Austria

Zobrazit více v PubMed

Adolphs R, Andler D. Investigating emotions as functional states distinct from feelings. Emot Rev. 2018;10(3):191–201. doi: 10.1177/1754073918765662. PubMed DOI PMC

Adriaense JEC, Koski SE, Huber L, Lamm C. Challenges in the comparative study of empathy and related phenomena in animals. Neurosci Biobehav Rev. 2020;112:62–82. doi: 10.1016/j.neubiorev.2020.01.021. PubMed DOI

Adriaense JEC, Martin JS, Schiestl M, Lamm C, Bugnyar T. Negative emotional contagion and cognitive bias in common ravens (Corvus corax) Proc Natl Acad Sci. 2019;116(23):11547–11552. doi: 10.1073/pnas.1817066116. PubMed DOI PMC

Adriaense JEC, Martin JS, Schiestl M, Lamm C, Bugnyar T (2019b) Reply to Vonk: disentangling emotional contagion from its underlying causes. Proc National Acad Sci 201910556 PubMed PMC

Anderson DJ, Adolphs R. A framework for studying emotions across species. Cell. 2014;157(1):187–200. doi: 10.1016/j.cell.2014.03.003. PubMed DOI PMC

Ash H, Buchanan-Smith HM. The long-term impact of infant rearing background on the affective state of adult common marmosets (Callithrix jacchus) Appl Anim Behav Sci. 2016;174:128–136. doi: 10.1016/j.applanim.2015.10.009. PubMed DOI PMC

Aureli F, van Schaik CP. Post-conflict behaviour in long-tailed macaques (Macaca fascicularis) II Coping with the uncertainty. Ethology. 1991;89(2):101–114. doi: 10.1111/j.1439-0310.1991.tb00297.x. DOI

Baciadonna L, Duepjan S, Briefer EF, Padilla de la Torre M, Nawroth C. Looking on the bright side of livestock emotions—the potential of their transmission to promote positive welfare. Front Veter Sci. 2018;5:218. doi: 10.3389/fvets.2018.00218. PubMed DOI PMC

Bassett L, Buchanan-Smith HM, McKinley J, Smith T. Effects of training on stress-related behavior of the common marmoset (Callithrix jacchus) in relation to coping with routine husbandry procedures. J Appl Anim Welfare Sci. 2003;6:221–233. doi: 10.1207/S15327604JAWS0603_07. PubMed DOI

Bates D, Maechler M, Bolker B, Walker S. Fitting linear mixed-effects models using lme4. J Stat Softw. 2015;67(1):1–48. doi: 10.18637/jss.v067.i01. DOI

Bateson M, Desire S, Gartside SE, Wright GA. Agitated honeybees exhibit pessimistic cognitive biases. Curr Biol. 2011;21(12):1070–1073. doi: 10.1016/j.cub.2011.05.017. PubMed DOI PMC

Bateson M, Nettle D. Development of a cognitive bias methodology for measuring low mood in chimpanzees. PeerJ. 2015;3:e998. doi: 10.7717/peerj.998. PubMed DOI PMC

Berthier JM, Semple S. Observing grooming promotes affiliation in Barbary macaques. Proc Royal Soc B. 2018;285(1893):20181964. doi: 10.1098/rspb.2018.1964. PubMed DOI PMC

Bethell EJ. A “how-to” guide for designing judgment bias studies to assess captive animal welfare. J Appl Anim Welf Sci. 2015;18(sup1):S18–S42. doi: 10.1080/10888705.2015.1075833. PubMed DOI

Bethell EJ, Holmes A, MacLarnon A, Semple S. Cognitive bias in a non-human primate: husbandry procedures influence cognitive indicators of psychological well-being in captive rhesus macaques. Anim Welf. 2012;21(2):185–195. doi: 10.7120/09627286.21.2.185. DOI

Bezerra BM, Souto A. Structure and usage of the vocal repertoire of Callithrix jacchus. Int J Primatol. 2008;29:671–701. doi: 10.1007/s10764-008-9250-0. DOI

Boissy A, et al. Assessment of positive emotions in animals to improve their welfare. Physiol Behav. 2007;92(3):375–397. doi: 10.1016/j.physbeh.2007.02.003. PubMed DOI

Briefer EF. Vocal contagion of emotions in non-human animals. Proc R Soc B. 2018;285(1873):20172783. doi: 10.1098/rspb.2017.2783. PubMed DOI PMC

Briefer EF, Tettamanti F, McElligott AG. Emotions in goats: mapping physiological, behavioural and vocal profiles. Anim Behav. 2015;99:131–143. doi: 10.1016/j.anbehav.2014.11.002. DOI

Brilot BO, Asher L, Bateson M. Stereotyping starlings are more ‘pessimistic’. Anim Cogn. 2010;13(5):721–731. doi: 10.1007/s10071-010-0323-z. PubMed DOI

Brügger RK, Willems EP, Burkart JM (2021) Do marmosets understand others’ conversations? A thermography approach. Sci Adv 7(6): eabc8790 PubMed PMC

Bučková K, Špinka M, Hintze S. Pair housing makes calves more optimistic. Sci Rep. 2019;9(1):1–9. doi: 10.1038/s41598-019-56798-w. PubMed DOI PMC

Burkart JM, Allon O, Amici F, Fichtel C, Finkenwirth C, et al. The evolutionary origin of human hyper-cooperation. Nat Commun. 2014;5(1):1–9. doi: 10.1038/ncomms5747. PubMed DOI

Burkart JM, Fehr E, Efferson C, van Schaik CP. Other-regarding preferences in a non-human primate: Common marmosets provision food altruistically. Proc Natl Acad Sci. 2007;104(50):19762–19766. doi: 10.1073/pnas.0710310104. PubMed DOI PMC

Burkart JM, Hrdy SB, van Schaik CP. Cooperative breeding and human cognitive evolution. Evolution Anthropol. 2009;18(5):175–186. doi: 10.1002/evan.20222. DOI

Burkart JM, van Schaik CP. Cognitive consequences of cooperative breeding in primates? Anim Cogn. 2010;13(1):1–19. doi: 10.1007/s10071-009-0263-7. PubMed DOI

Burkett JP, Andari E, Johnson ZV, Curry DC, de Waal FB, Young LJ. Oxytocin-dependent consolation behaviour in rodents. Science. 2016;351(6271):375–378. doi: 10.1126/science.aac4785. PubMed DOI PMC

Cilia J, Piper DC. Marmoset conspecific confrontation: an ethologically-based model of anxiety. Pharmacol Biochem Behav. 1997;58(1):85–91. doi: 10.1016/S0091-3057(96)00376-0. PubMed DOI

Clay Z, de Waal FB (2015) Sex and strife: post-conflict sexual contacts in bonobos. In Bonobo Cognition and Behaviour (pp. 67–88). Brill

Clore GL (2018) Emotions: Causes and Consequences. In: Fox AS, Lapate RC, Shackman AJ, Davidson RJ (Eds.) (2018) The nature of emotion: fundamental questions. Oxford University Press

de Waal FB. Putting the altruism back into altruism: The evolution of em- pathy. Annu Rev Psychol. 2008;59:279–300. doi: 10.1146/annurev.psych.59.103006.093625. PubMed DOI

De Waal FB. What is an animal emotion? Ann N Y Acad Sci. 2011;1224(1):191–206. doi: 10.1111/j.1749-6632.2010.05912.x. PubMed DOI

Decety J. The neural pathways, development and functions of empathy. Curr Opin Behav Sci. 2015;3:1–6. doi: 10.1016/j.cobeha.2014.12.001. DOI

Dezecache G, Jacob P, Grezes J. Emotional contagion: its scope and limits. Trends Cogn Sci. 2015;19(6):297–299. doi: 10.1016/j.tics.2015.03.011. PubMed DOI

Digby LJ, Barreto CE. Social organization in a wild population of Callithrix jacchus. Folia Primatol. 1993;61(3):123–134. doi: 10.1159/000156739. PubMed DOI

Douglas C, Bateson M, Walsh C, Bédué A, Edwards SA. Environmental enrichment induces optimistic cognitive biases in pigs. Appl Anim Behav Sci. 2012;139(1–2):65–73. doi: 10.1016/j.applanim.2012.02.018. DOI

Edgar JL, Nicol CJ, Clark CCA, Paul ES. Measuring empathic responses in animals. Appl Anim Behav Sci. 2012;138(3–4):182–193. doi: 10.1016/j.applanim.2012.02.006. DOI

Epple G. Comparative studies on vocalization in marmoset monkeys (Hapalidae) Folia Primatol. 1968;8(1):1–40. doi: 10.1159/000155129. PubMed DOI

Epple G. Quantitative studies on scent marking in the marmosets (Callithrix jacchus) Folia Primatol. 1970;13:48–62. doi: 10.1159/000155308. PubMed DOI

Erb WM, Porter LM. Mother's little helpers: What we know (and don't know) about cooperative infant care in callitrichines. Evolution Anthropol. 2017;26(1):25–37. doi: 10.1002/evan.21516. PubMed DOI

Ermatinger FA, Brügger RK, Burkart JM. The use of infrared thermography to investigate emotions in common marmosets. Physiol Behav. 2019;211:112672. doi: 10.1016/j.physbeh.2019.112672. PubMed DOI

Eysenck MW, Mogg K, May J, Richards A, Mathews A. Bias in interpretation of ambiguous sentences related to threat in anxiety. J Abnorm Psychol. 1991;100:144–150. doi: 10.1037/0021-843X.100.2.144. PubMed DOI

Finkenwirth C, van Schaik C, Ziegler TE, Burkart JM. Strongly bonded family members in common marmosets show synchronized fluctuations in oxytocin. Physiol Behav. 2015;151:246–251. doi: 10.1016/j.physbeh.2015.07.034. PubMed DOI PMC

Gordon DJ, Rogers LJ. Cognitive bias, hand preference and welfare of common marmosets. Behav Brain Res. 2015;287:100–108. doi: 10.1016/j.bbr.2015.03.037. PubMed DOI

Gygax L. The A to Z of statistics for testing cognitive judgement bias. Anim Behav. 2014;95:59–69. doi: 10.1016/j.anbehav.2014.06.013. DOI

Harding EJ, Paul ES, Mendl M. Animal behaviour: cognitive bias and affective state. Nature. 2004;427(6972):312. doi: 10.1038/427312a. PubMed DOI

Harrison ML, Tardif SD. Species differences in response to intruders in Callithrix jacchus and Saguinus oedipus. Int J Primatol. 1988;10:343–362. doi: 10.1007/BF02737421. DOI

Hatfield E, Cacioppo JT, Rapson RL. Emotional Contagion. Cambridge: Cambridge University Press; 1994.

Hintze S, Melotti L, Colosio S, Bailoo JD, Boada-Saña M, Würbel H, Murphy E. A cross-species judgement bias task: integrating active trial initiation into a spatial Go/No-go task. Sci Rep. 2018;8(1):1–13. doi: 10.1038/s41598-018-23459-3. PubMed DOI PMC

Iigaya K, Jolivald A, Jitkrittum W, Gilchrist ID, Dayan P, Paul E, Mendl M. Cognitive bias in ambiguity judgements: using computational models to dissect the effects of mild mood manipulation in humans. PLoS ONE. 2016;11(11):e0165840. doi: 10.1371/journal.pone.0165840. PubMed DOI PMC

Isern-Mas C, Gomila A. Making sense of emotional contagion. Humana Mente J Philos Stud. 2019;12(35):71–100.

Kato Y, Gokan H, Oh-Nishi A, et al. Vocalizations associated with anxiety and fear in the common marmoset (Callithrix jacchus) Behav Brain Res. 2014;275:43–52. doi: 10.1016/j.bbr.2014.08.047. PubMed DOI

Košťál Ľ, Skalná Z, Pichová K (2020) Use of cognitive bias as a welfare tool in poultry. J Animal Sci PubMed PMC

Kramer KL. Cooperative breeding and its significance to the demographic success of humans. Annu Rev Anthropol. 2010;39:417–436. doi: 10.1146/annurev.anthro.012809.105054. DOI

Lagisz M, Zidar J, Nakagawa S et al (2020) Optimism, pessimism and judgement bias in animals: a systematic review and meta-analysis. Neurosci Biobehav Rev PubMed

Lakin JL, Chartrand TL. Using nonconscious behavioural mimicry to create affiliation and rapport. Psychol Sci. 2003;14(4):334–339. doi: 10.1111/1467-9280.14481. PubMed DOI

Lalot M, Ung D, Péron F, d’Ettorre P, Bovet D. You know what? I’m happy. Cognitive bias is not related to personality but is induced by pair-housing in canaries (Serinus canaria) Behav Proc. 2017;134:70–77. doi: 10.1016/j.beproc.2016.09.012. PubMed DOI

Lazaro-Perea C. Intergroup interactions in wild common marmosets (Callithrix jacchus): Territorial defence and assessment of neighbours. Anim Behav. 2001;62:11–12. doi: 10.1006/anbe.2000.1726. DOI

Lazaro-Perea C, Snowdon CT, de Fátima Arruda M. Scent-marking behavior in wild groups of common marmosets (Callithrix jacchus) Behav Ecol Sociobiol. 1999;46(5):313–324. doi: 10.1007/s002650050625. DOI

MacDougall-Shackleton SA, Bonier F, Romero LM, Moore IT (2019) Glucocorticoids and “stress” are not synonymous. Integrat Organ Biol 1(1): obz017 PubMed PMC

MacLeod AK, Byrne A. Anxiety, depression, and the anticipation of future po- sitive and negative experiences. J Abnorm Psychol. 1996;105:286–289. doi: 10.1037/0021-843X.105.2.286. PubMed DOI

Maestripieri D, Schino G, Aureli F, Troisi A. A modest proposal: displacement activities as an indicator of emotions in primates. Anim Behav. 1992;44(5):967–979. doi: 10.1016/S0003-3472(05)80592-5. DOI

Manciocco A, Chiarotti F, Vitale A. Effects of positive interaction with caretakers on the behaviour of socially housed common marmosets (Callithrix jacchus) Appl Anim Behav Sci. 2009;120(1–2):100–107. doi: 10.1016/j.applanim.2009.05.007. DOI

Martin JS, Koski SE, Bugnyar T, Jaeggi AV, Massen JJM. Prosociality, social tolerance and partner choice facilitate mutually beneficial cooperation in common marmosets, Callithrix jacchus. Anim Behav. 2021;173:115–136. doi: 10.1016/j.anbehav.2020.12.016. DOI

Martin JS, Massen JJ, Šlipogor V, Bugnyar T, Jaeggi AV, Koski SE. The EGA+ GNM framework: An integrative approach to modelling behavioural syndromes. Methods Ecol Evol. 2019;10(2):245–257. doi: 10.1111/2041-210X.13100. DOI

Massen JJ, Behrens F, Martin JS, Stocker M, Brosnan SF (2019) A comparative approach to affect and cooperation. Neurosci Biobehav Rev 370–387 PubMed

Massen JJ, Gallup AC. Why contagious yawning does not (yet) equate to empathy. Neurosci Biobehav Rev. 2017;80:573–585. doi: 10.1016/j.neubiorev.2017.07.006. PubMed DOI

Massen JJ, Šlipogor V, Gallup AC. An Observational investigation of behavioral contagion in common marmosets (Callithrix jacchus): indications for contagious scent-marking. Front Psychol. 2016;7:1190. doi: 10.3389/fpsyg.2016.01190. PubMed DOI PMC

Mathews A, MacLeod C. Cognitive approaches to emotion and emotional dis- orders. Annu Rev Psychol. 1994;45(1):25–50. doi: 10.1146/annurev.ps.45.020194.000325. PubMed DOI

McGuire MC, Vonk J. Gorillas (Gorilla gorilla gorilla) fail to learn abstract cues of differential outcomes in a novel cognitive bias test. Animal Behavior Cogn. 2018;5(1):103–117. doi: 10.26451/abc.05.01.08.2018. DOI

McGuire MC, Vonk J, Fuller G, Allard S. Using an ambiguous cue paradigm to assess cognitive bias in gorillas (Gorilla gorilla gorilla) during a forage manipulation. Anim Behav Cogn. 2017;4:70–83.

McIntosh DN. Spontaneous facial mimicry, liking and emotional contagion. Polish Psycholog Bull. 2006;37(1):31.

Mendl M, Burman OH, Parker RM, Paul ES. Cognitive bias as an indicator of animal emotion and welfare: Emerging evidence and underlying mechanisms. Appl Anim Behav Sci. 2009;118(3–4):161–181. doi: 10.1016/j.applanim.2009.02.023. DOI

Mendl M, Burman OH, Paul ES. An integrative and functional framework for the study of animal emotion and mood. Proc R Soc B. 2010;277(1696):2895–2904. doi: 10.1098/rspb.2010.0303. PubMed DOI PMC

Meyza KZ, Bartal IBA, Monfils MH, Panksepp JB, Knapska E. The roots of empathy: through the lens of rodent models. Neurosci Biobehav Rev. 2017;76:216–234. doi: 10.1016/j.neubiorev.2016.10.028. PubMed DOI PMC

Miss FM, Burkart JM. Corepresentation during joint action in marmoset monkeys (Callithrix jacchus) Psychol Sci. 2018;29(6):984–995. doi: 10.1177/0956797618772046. PubMed DOI

Nakahashi W, Ohtsuki H. Evolution of emotional contagion in group-living animals. J Theor Biol. 2018;440:12–20. doi: 10.1016/j.jtbi.2017.12.015. PubMed DOI

Neal SJ, Caine NG. Scratching under positive and negative arousal in common marmosets (Callithrix jacchus). American journal of primatology, 78(2), 216–226. Neurosci Biobehav Rev. 2016;80:573–585. PubMed

Neville V, Nakagawa S, Zidar J, et al. Pharmacological manipulations of judgement bias: a systematic review and meta-analysis. Neurosci Biobehav Rev. 2020;108:269–286. doi: 10.1016/j.neubiorev.2019.11.008. PubMed DOI PMC

Nygren TE, Isen AM, Taylor PJ, Dulin J. The influence of positive affect on the decision rule in risky situations. Org Behav Hum Decis Proc. 1996;66:59–72. doi: 10.1006/obhd.1996.0038. DOI

Paul ES, Harding EJ, Mendl M. Measuring emotional processes in animals: The utility of a cognitive approach. Neurosci Biobehav Rev. 2005;29(3):469–491. doi: 10.1016/j.neubiorev.2005.01.002. PubMed DOI

Perdue BM. Mechanisms underlying cognitive bias in nonhuman primates. Animal Behavior Cogn. 2017;4(1):105–118. doi: 10.12966/abc.08.02.2017. DOI

Pessoa L (2013) The cognitive-emotional brain: From interactions to integration. MIT press

Péter A (2017) Solomon Coder (version beta 17.03.22): A simple and free solution for behavior coding. Available online at: https://solomon.andraspeter.com/

Pomerantz O, Terkel J, Suomi SJ, Paukner A. Stereotypic head twirls, but not pacing, are related to a ‘pessimistic’-like judgment bias among captive tufted capuchins (Cebus apella) Anim Cogn. 2012;15(4):689–698. doi: 10.1007/s10071-012-0497-7. PubMed DOI PMC

Preston SD, de Waal FBM. Empathy: its ultimate and proximate bases. Behav Brain Sci. 2002;25:1–72. doi: 10.1017/S0140525X02000018. PubMed DOI

R Core Team (2019/13) R: A language and environment for statistical computing (R Foundation for Statistical Computing, Vienna, Austria

Reimert I, Fong S, Rodenburg TB, Bolhuis JE. Emotional states and emotional contagion in pigs after exposure to a positive and negative treatment. Appl Anim Behav Sci. 2017;193:37–42. doi: 10.1016/j.applanim.2017.03.009. DOI

Roelofs S, Boleij H, Nordquist RE, van der Staay FJ. Making decisions under ambiguity: judgment bias tasks for assessing emotional state in animals. Front Behav Neurosci. 2016;10:119. doi: 10.3389/fnbeh.2016.00119. PubMed DOI PMC

Russell JA. A circumplex model of affect. J Pers Soc Psychol. 1980;39(6):1161. doi: 10.1037/h0077714. DOI

Russell YI, Phelps S. How do you measure pleasure? A discussion about intrinsic costs and benefits in primate allogrooming. Biol Philos. 2013;28(6):1005–1020. doi: 10.1007/s10539-013-9372-4. DOI

Rygula R, Pluta H, Popik P. Laughing rats are optimistic. PLoS ONE. 2012;7(12):e51959. doi: 10.1371/journal.pone.0051959. PubMed DOI PMC

Saito Y, Yuki S, Seki Y, Kagawa H, Okanoya K. Cognitive bias in rats evoked by ultrasonic vocalizations suggests emotional contagion. Behav Proc. 2016;132:5–11. doi: 10.1016/j.beproc.2016.08.005. PubMed DOI

Schaffner C, Aureli F. Relationship assessment through emotional mediation. Behaviour. 2002;139(2):393–420. doi: 10.1163/156853902760102726. DOI

Schiel N, Souto A. The common marmoset: An overview of its natural history, ecology and behavior. Devel Neurobio. 2017;77:244–262. doi: 10.1002/dneu.22458. PubMed DOI

Schino G, Aureli F. Reciprocal altruism in primates: partner choice, cognition, and emotions. Adv Study Behav. 2009;39:45–69. doi: 10.1016/S0065-3454(09)39002-6. DOI

Schino G, Massimei R, Pinzaglia M, Addessi E. Grooming, social rank and ‘optimism’in tufted capuchin monkeys: a study of judgement bias. Anim Behav. 2016;119:11–16. doi: 10.1016/j.anbehav.2016.06.017. DOI

Schubiger MN, Wüstholz FL, Wunder A, Burkart JM. High emotional reactivity toward an experimenter affects participation, but not performance, in cognitive tests with common marmosets (Callithrix jacchus) Anim Cogn. 2015;18(3):701–712. doi: 10.1007/s10071-015-0837-5. PubMed DOI

Semple S, Harrison C, Lehmann J. Grooming and Anxiety in B arbary Macaques. Ethology. 2013;119(9):779–785. doi: 10.1111/eth.12119. DOI

Šlipogor V, Gunhold-de Oliveira T, Tadić Z, Massen JJM, Bugnyar T. Consistent inter-individual differences in common marmosets (Callithrix jacchus) in Boldness-Shyness, Stress-Activity and Exploration-Avoidance. Am J Primatol. 2016;78:961–973. doi: 10.1002/ajp.22566. PubMed DOI PMC

Šlipogor V, Massen JJ, Schiel N, Souto A, Bugnyar T (2021) Temporal consistency and ecological validity of personality structure in common marmosets (Callithrix jacchus): A unifying field and laboratory approach. Am J Primatol e23229. PubMed PMC

Symonds MR, Moussalli A. A brief guide to model selection, multimodel inference and model averaging in behavioural ecology using Akaike’s information criterion. Behav Ecol Sociobiol. 2011;65(1):13–21. doi: 10.1007/s00265-010-1037-6. DOI

Tardif SD, Richter CB. Competition for a desired food in family groups of the common marmoset (Callithrix jacchus) and the cotton-top tamarin (Saguinus oedipus) Lab Anim Sci. 1981;31(1):52. PubMed

Troisi A. Displacement activities as a behavioral measure of stress in nonhuman primates and human subjects. Stress. 2002;5(1):47–54. doi: 10.1080/102538902900012378. PubMed DOI

Troisi A, Schino G, D'Antoni M, Pandolfi N, Aureli F, D'Amato FR. Scratching as a behavioral index of anxiety in macaque mothers. Behav Neural Biol. 1991;56(3):307–313. doi: 10.1016/0163-1047(91)90469-7. PubMed DOI

Ueno M, Yamada K, Nakamichi M. Emotional states after grooming interactions in Japanese macaques (Macaca fuscata) J Comp Psychol. 2015;129(4):394. doi: 10.1037/a0039688. PubMed DOI

Watson CF, Caldwell CA. Neighbor effects in marmosets: social contagion of agonism and affiliation in captive Callithrix jacchus. Am J Primatol. 2010;72(6):549–558. doi: 10.1002/ajp.20805. PubMed DOI

Yamamoto S, Takimoto A. Empathy and fairness: Psychological mechanisms for eliciting and maintaining prosociality and cooperation in primates. Social Justice Res. 2012;25(3):233–255. doi: 10.1007/s11211-012-0160-0. DOI