Where are we in the study of animal emotions?
The study of emotion is rife with debate over issues as fundamental as how to define emotion, and such disputes are particularly common in the nonhuman animal emotion literature. Here, we seek to address some of these issues, especially in terms of how they relate to animal research. Definitional issues are prevalent; clear definitions are often not given of crucial terms, including 'emotion,' and even where provided, such terms may be used inconsistently throughout a single paper. Further disagreement over the structure of emotions, and the nature of conscious experiences involved, leads to consistent differences in authors' criteria for emotions. We concur with those who believe that animals experience emotions and believe that animal emotions should be studied in their own right, not only as they compare to those of humans. We also propose several avenues for future research that we believe will further our understanding of animal emotions. First, the use of multiple measurement methods to assess emotional responses is most likely to provide the information necessary to distinguish between various states and opens the field to more research in harder-to-study species, such as marine mammals. Second, researchers should also endeavor to increase the range of emotions studied, particularly positive ones, in order to move toward a more balanced range of studied states. Finally, we believe that several aspects of personality research would prove beneficial to the study of animal emotions, particularly the distinction between trait and state emotion and the use of the rating method. WIREs Cogn Sci 2016, 7:354-362. doi: 10.1002/wcs.1399 For further resources related to this article, please visit the WIREs website.