Tackling challenges in the study of animal emotions: a review.

The study of animal emotion can be the source of much confusion and lack of clarity. Researchers may talk past each other when discussing their work, and communication with stakeholders can result in misunderstandings about what is actually being studied and what has been found out. Here, we identify some key challenges in studying animal emotion and offer ways forward for tackling them. We begin by considering the uses of, and debates about, terminology and definitions, offering a prescriptive, reinforcement-based definition that can facilitate empirical research. Highlighting difficulties encountered when transposing human constructs of "affect", "emotion", and "mood" to non-humans, we identify three pathways that may help in this endeavour - translation of: emotion concepts (theory-focused); emotion correlates (subject-focused), and emotion contexts (event-focused). For emotion concepts, we consider the arguments for discrete and dimensional views of animal affect, and the temporal distinction between short-term emotions and longer-term moods. We then discuss how translation of emotion correlates and contexts can be used to identify affective states in animals; an essential prerequisite for the validation of animal emotion indicators, including facial and vocal behaviours, which we use as examples. We conclude by considering the elusive, subjective component of animal emotion.