Lateralized behaviour in dogs during positive anticipation

Recent research has used behavioural asymmetries in dogs as an indirect measure of their emotional states from inferred asymmetries in brain activity. Different hypotheses predict differences in behaviour based on emotional salience (right-hemisphere hypothesis), valence (valence hypothesis) or motivation (approach–withdrawal hypothesis). As testing different hypotheses requires having a measure of the consistency of a lateralized response across stimuli of similar emotional significance, we investigated dogs' responses to two emotionally positive and approach-motivating stimuli (food and toy) presented within an apparatus in which dogs could see the positive stimulus (anticipatory phase) before being given access to it. Moreover, to assess the degree to which expressions of lateralized behaviour are similar across different functional responses to an emotionally competent stimulus (and, thus, to explore the generalizability of different hypotheses), biases were analysed both at the level of sensory processing (i.e. lateralized eye use) as well as ‘postprocessing’ motor action (i.e. lateralized tail-wagging behaviour) during stimulus inspection. Overall, dogs showed a right-eye/left-hemisphere dominance when inspecting the food, but no population level bias for the toy; although they displayed consistent individual level biases. This difference cannot be explained by simply referring to the stimuli with regards to their general emotional salience (right-hemisphere hypothesis), valence (valence hypothesis), or general motivational tendencies (approach–withdrawal hypothesis). In relation to tail wagging, laterality patterns for both stimuli involved considerable inter-/intraindividual variability, with no common directional bias at a population level. Expressions of lateralized activity can therefore vary between sensory perceptual and expressive motor processes. These results suggest that emotion-related behavioural/brain lateralization reflects a complex phenomenon that probably involves processes modulated by multiple factors. The contribution of laterality patterns to informing assessments of animals' emotions might be more limited than generally assumed.