Defining social reward: A systematic review of human and animal studies

Social rewards are strong drivers of behavior and fundamental to well-being, yet there is a lack of consensus regarding what actually defines a reward as “social.” Because a systematic overview of existing social reward operationalizations is currently absent, a review of the literature seems necessary to advance toward a unified framework and to better guide research and theory. To bridge this gap, we preregistered and conducted the first comprehensive systematic review of human and animal experimental studies that used the term “social reward” and charted existing operationalizations, revealing the implicit and explicit definitions used in the field. Stimulus characteristics and measures of social reward were extracted from a total of 384 studies encompassing 42,118 participants and subjects. We provide detailed summaries of these elements, stratified by species (human/animal) and study type (behavioral, brain imaging, pharmacological, and physiological). Two main aspects were found to account for most of the difference in operationalizations: the sensory richness of a stimulus (intimacy) and engagement in social interaction (i.e., the synchronous observation and action between at least two individuals, viz., immediacy). Drawing insights from second-person neuroscience approaches and theoretical models in the field of human–computer interaction, we propose that human and animal research can greatly benefit from considering these properties, as they have important theoretical and practical consequences for human and translational research, with far-reaching implications for neighboring research fields such as those pertaining to social media and the development of artificial intelligence.