Testing of behavioural asymmetries as markers for brain lateralization of emotional states in pet dogs: A critical review.

Domestic dogs (Canis familiaris) hold a unique position in human society, particularly in their role as social companions; as such, it is important to understand their emotional lives. There has been growing interest in studying behavioural biases in dogs as indirect markers (reflecting lateralized brain activity) of their emotional states. In this paper, we not only review the previous literature on emotion-related behavioural lateralization in dogs, but also propose and apply the concept of evidential weight to previous research. This allows us to examine different hypotheses about emotion-related brain asymmetries (i.e., Right-Hemisphere-, Valence-, Approach-Withdrawal-Hypothesis) on the basis of a "likelihood-ist" concept of evidence. We argue that previous studies have not been able to discriminate well between competing hypotheses and tended to focus on confirmation bias than critically assess different hypotheses; as such there is a strong case for more systematic investigation to pull these theories apart. We present the areas for future research and explain their importance for understanding the emotional lives of dogs.