Edited by Frans B. M. de Waal, Emory University, Atlanta, GA, and approved April 19, 2019 (received for review October 3, 2018)
To successfully and efficiently live in social groups, we need information about each other’s emotions. Emotional contagion has been suggested to facilitate such information transmission, yet it remains difficult to measure this in animals. Previous research has often focused on overt behavior but lacked additional methods for investigating emotional valence. This study provides a solution by integrating data on behavior and responses to a cognitive bias test, which is designed to infer a subject’s underlying emotional state. We demonstrate that after witnessing a conspecific in a negative state, ravens perform in a negatively biased manner on a judgment task. Our findings thus suggest negative emotional contagion in ravens, and in turn advance our understanding of the evolution of empathy.
Emotional contagion is described as an emotional state matching between subjects, and has been suggested to facilitate communication and coordination in complex social groups. Empirical studies typically focus on the measurement of behavioral contagion and emotional arousal, yet, while highly important, such an approach often disregards an additional evaluation of the underlying emotional valence. Here, we studied emotional contagion in ravens by applying a judgment bias paradigm to assess emotional valence. We experimentally manipulated positive and negative affective states in demonstrator ravens, to which they responded with increased attention and interest in the positive condition, as well as increased redirected behavior and a left-eye lateralization in the negative condition. During this emotion manipulation, another raven observed the demonstrator’s behavior, and we used a bias paradigm to assess the emotional valence of the observer to determine whether emotional contagion had occurred. Observers showed a pessimism bias toward the presented ambiguous stimuli after perceiving demonstrators in a negative state, indicating emotional state matching based on the demonstrators’ behavioral cues and confirming our prediction of negative emotional contagion. We did not find any judgment bias in the positive condition. This result critically expands upon observational studies of contagious play in ravens, providing experimental evidence that emotional contagion is present not only in mammalian but also in avian species. Importantly, this finding also acts as a stepping stone toward understanding the evolution of empathy, as this essential social skill may have emerged across these taxa in response to similar socioecological challenges.
Author contributions: J.E.C.A. and T.B. designed research; J.E.C.A. and M.S. performed research; J.S.M. analyzed data; and J.E.C.A., J.S.M., C.L., and T.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1817066116/-/DCSupplemental.
Published under the PNAS license.
