Sensory Laterality Horses are one-sided, in that they usually prefer to use one eye, ear or nostril over the other under particular circumstances. Science attributes this sensory laterality to the processing of different types of information in one or other of the two brain hemispheres. Generally, horses prefer using the left eye to observe novel objects and humans, and this preference is more marked in emotional situations and when confronted with unknown persons. Therefore, the horse’s visual laterality provides a good means of assessing whether horses are making emotional or rational decisions during training or in human-horse interactions. A preference for the left eye may indicate that a horse will prefer a certain eye when making either emotional or rational decisions. A particularly strong laterality can indicate that a horse cannot deal with certain training situations or is emotionally affected by a particular human or the training situation itself.
Visual Laterality in the Domestic Horse (Equus Caballus) in Passive and Active Interaction with Humans
Most horses have a side on which they are easier to handle, and a direction they favour when working on a circle, and recent studies have suggested a correlation between emotion and visual laterality when horses observe inanimate objects. We investigated whether laterality also varies in association with people. We gave horses the choice of entering a chute to left or right, with and without the passive presence of a person unknown to them. The left eye was preferred for scanning under both conditions, but significantly more so when a person was present. Traditionally, riders handle horses from the left, so we repeated the experiment with horses specifically trained on both sides. Again, there was a consistent preference for left eye scanning in the presence of a person, whether known to the horses or not. We also examined horses interacting with a person, using both traditionally and bilaterally trained horses. Both groups showed left eye preference for viewing the person, with no significant effect of training. For those horses tested under both passive and interactive conditions, the left eye was preferred significantly more during interaction. We suggest that most horses prefer to use their left eye for assessment and evaluation, and that there is an emotional aspect to the choice which may be positive or negative, depending on the circumstances. We believe these results have important implications both for welfare and efficient training: emotional laterality effects need to be taken into account in development of training methods.
Monocular learning and visual acuity in domstic horses (Equus caballus)
For this new study we are covering one of the horse’s eyes with a mask produced by the company SAM, Sattlerei Ansorge, Munich. We are studying the monocular learning abilities and visual acuity of horses when discriminating striped patterns on a digital picture frame (provided by the company 2direct) and we are measuring a possible stress response by analysing the cortisol in each horse’s saliva.
We expect the results to show that horses with either left or right eye covered 1) may differ in their learning abilities and learning speed, 2) may experience stress, which could affect the learning capacity, or 3) may show their laterality is caused by differences in the visual acuity of each eye.