Equid Emotions and Laterality: Is there a Connection?

Does your horse give "dirty" looks? Rather than trying to read his expression, you might be able get some clues about how your horse really feels about objects by paying attention to which eye he uses to observe them. French behaviorists reported that horses explore and process information about various objects differently, depending on the emotional importance of the item.

According to co-author Martine Hausberger, PhD, director of research at the Centre National de Recherche Scientifique at the University of Rennes in France, "In the past few years, researchers have suggested that a link exists between a lateralized response and emotions in animals."

Brain lateralization refers to the hypothesis that the left and right sides of the brain are responsible for different functions. Previous studies have shown that horses will use their left eye--which is controlled by the right side of the brain--to explore a new object. More "emotional" horses spend a longer period of time with their left eye fixed on an unfamiliar object.

The purpose of this study was to determine whether horses experienced motor laterality (a preference to observe an object from one side or the other) and whether the laterality was related to their emotional response.

The authors observed the reactions of 38 purebred Arabian mares. Mares were confronted with one of three objects:

  • A bucket (associated with feeding--a positive emotional value);
  • A small orange plastic traffic cone (a novel object for a neutral emotional value), and;
  • A white shirt typically worn by veterinarians (negative emotional value).

Researchers found that mares used their right eye more frequently to explore a novel object (the cone) and their left eye to explore the negative object (shirt). For the positive item, the bucket, mares typically used their binocular field for exploration. The mares also took a significantly longer period of time to explore the negative object compared to either the cone or the bucket.

"These data suggest that the left side of the brain (which controls the right eye) is used to explore novel items, but the right side of the brain is important for processing negative emotional responses," said Hausberger. "Also, since the mares used their binocular vision for the bucket, positive emotions may be processed by both sides of the brain."

According to Hausberger, the way horses look at objects might therefore give an indication of the "valence" they give to this object: intriguing (low emotion), fear inducing (and therefore prone to induce a behavioral reaction) or familiar and positive. This would give handlers a way to understand the horse's perception of its world. Horse owners might not be aware of or share these representations, so observing the way horses look at objects could help owners to prevent--or at least understand--their animals' stronger reactions.

Future research will look at the effects of development and training on these lateralized visual responses to objects.

The study, "Laterality and emotions: Visual laterality in the domestic horse (Equus caballus) differs with objects' emotional value," was published in the June 9th, 2008, edition of Physiology and Behavior.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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