Visual laterality in the domestic horse (Equus caballus) differs with objects’ emotional value
Résumé
Lateralization of emotions has received great attention in the last decades, both in humans and
animals, but little interest has been given to side bias in perceptual processing. Here, we
investigated the influence of the emotional valence of stimuli on visual and olfactory
explorations by horses, a large mammalian species with two large monocular visual fields and
almost complete decussation of optic fibres. We confronted 38 Arab mares to three objects
with either a positive, negative or neutral emotional valence (novel object). The results
revealed a gradient of exploration of the 3 objects according to their emotional value and a
clear asymmetry in visual exploration. When exploring the novel object, mares used
preferentially their right eyes, while they showed a slight tendency to use their left eyes for
the negative object. No asymmetry was evidenced for the object with the positive valence.
Our data confirm the role of the left hemisphere in assessing novelty in horses like in many
vertebrate species and the possible role of the right hemisphere in processing negative
emotional responses. Our findings also suggest the importance of both hemispheres in the
processing positive emotions. This study is, to our knowledge, the first to demonstrate clearly
that the emotional valence of a stimulus induces a specific visual lateralization pattern.