The role of the eyes in animal-human emotional communication

Emotional communication is crucial in social groups in order for individuals to signal their intentions and motivations. Previous research on interspecific emotional communication has primarily concentrated on documenting animals’ abilities to recognise human emotion. However, the ways in which animals signal about their emotions to humans has largely been overlooked. Such insights could have important implications for animal welfare assessments, particularly in relation to how positive emotions are communicated (providing an indicator of good welfare). For domestic animals, interspecific emotional communication could be highly adaptive to facilitate the human-animal relationship. Indeed, research on domestic animals has revealed advanced socio-cognitive abilities in the context of human-animal communicative behaviour (e.g. social cue use, individual recognition, and the attribution of attention to others), suggesting that domestic animals are an appropriate study species in which to explore interspecific emotional communication. This thesis investigates the role of a potential universal signal of positive emotions, narrowing of the eye aperture, in animal-human interactions. Articles I, II and III systematically examined slow blinking in domestic cats, a behaviour that had previously been anecdotally observed during interactions between humans and cats. Slow blinking involves a series of eye movements (half blinking, eye narrowing and eye closure) that act to narrow the eye aperture. These three articles specifically explore the role of slow blinking in emotional communication, including how both cats and humans perceive slow blinking as well as investigating underlying cognitive aspects of this behaviour in cats. Article IV then tested whether similar eye narrowing movements were present in other domestic species, namely dogs and horses, during a non-communicative positive human-animal interaction. Evidence was found that cats actively engage in human-initiated slow blink interactions and perceive these interactions as positive. In addition, shelter cats who produce salient responses to slow blinking are rehomed faster, indicating that humans have a preference for cats who slow blink. Furthermore, cats who present a lateral bias in paw use, which is linked to owners’ perceptions of their cats as being more affectionate, friendly, confident, obedient, active and less aggressive, responded more to slow blinking and had greater behavioural synchrony during cat-human slow blink interactions. Finally, eye narrowing movements in non-communicative contexts revealed varied results depending on the species, which may reflect the extent to which these species were aroused by the grooming stimulus used. These findings contribute to our understanding of positive emotions in domestic animals and the potential universality of emotional expressions, and have implications for assessing animals’ wellbeing, as well as stimulating further research in the area of animal emotion.