A groundbreaking study has unveiled that horses possess the ability to differentiate between expressions of joy and sadness in human facial movements and tones of voice. Researchers discovered that horses exhibited a greater interest in expressions of happiness compared to sadness, displaying heightened enthusiasm upon hearing cheerful sounds.

Emotions play a pivotal role in human interaction and communication, influencing cross-species communication as well.

Numerous animal species, including orangutans, pigeons, and domesticated animals, have been recognized for their capacity to detect human emotions. Dogs, cats, horses, and even goats have shown the ability to distinguish various human emotional expressions. While prior research predominantly concentrated on emotions such as joy and anger, lesser emphasis has been given to investigating sadness.

An international research team comprising scholars from the University of Turku, the French National Institute for Agriculture, Food, and the Environment (INRAE), and the University of Tours in France closely observed and analyzed equine behavior in response to human faces and corresponding sounds reflecting happiness or sadness. Heart rate measurements of the horses were also recorded during the experiment.

"Sadness is an intriguing emotion, as it is not only negatively charged but also represents a low arousal state. Previous studies have demonstrated that horses respond to high arousal emotions, like anger or joy. However, can they also detect cues of low arousal emotions, like sadness? We wanted to investigate whether horses can associate human expressions of sadness with the corresponding sounds, as they do with joy and anger," explained Plotine Jardat, lead author of the study and a doctoral researcher at the French National Institute for Agriculture, Food, and the Environment, as well as the University of Tours in France.

Horses Confused by Mismatch between Sad Facial Expression and Happy Tone

In the experimental setting, horses were positioned in front of two screens, one displaying a person with a joyful expression and the other with a sad expression. Simultaneously, sounds indicating happiness or sadness were played. The initial response of the horses indicated their ability to associate facial expressions and tones.

Researchers observed that most horses took longer to avert their gaze from the screen displaying an incongruent image (sad face and happy sound) than from the congruent one (matching facial expression and tone). In other words, during the first glance at the images, horses displayed confusion when faced with the mismatch between a sad expression and a happy tone, and vice versa. This suggests that horses can link human faces and tones when they express the same emotional state, whether it's sadness or joy.

"This is intriguing because it would mean that when horses observe our faces and hear our voices, they do not perceive them as separate stimuli, but can integrate them across different sensory modalities. One might imagine that they have a mental box labeled 'human sadness', which includes both the sad facial expression and the sad tone of voice," added Océane Liehrmann, a doctoral researcher from the University of Turku.

The research team has employed a similar setup in several previous experiments to study how animals process images and sounds and their compatibility. In earlier studies on anger and joy, as well as perception tests involving adults and children, horses exhibited a consistent pattern where they looked more at the image that did not match the heard sound. Researchers have inferred that horses engage more with the incongruent image due to their curiosity about the lack of synchrony between the visual and auditory cues.

Horses Showed More Interest in Happy Images and Greater Enthusiasm for Joyful Sounds

Researchers also noted that after the initial gaze, horses focused more on the screen displaying a joyful expression, gazing at it for longer periods and more frequently. Additionally, their heart rates seemed to rise more in response to a cheerful sound compared to a sad one. This suggests that horses had a higher state of arousal when exposed to a joyful sound.

According to the researchers, the observations can be explained by three hypotheses. Firstly, horses might be more drawn to images of joy due to increased motion in those images and more excited about cheerful sounds because of their acoustic attributes like tonal variations. Secondly, horses could associate happy faces with positive experiences and may prefer looking at expressions linked to pleasant memories. Thirdly, the horses might feel more positive when viewing joyful expressions and exhibit greater enthusiasm upon hearing cheerful sounds, a phenomenon known as "emotional contagion." Emotional contagion refers to the observer's emotional state aligning with the perceived individual's emotional state. While this phenomenon has been described in humans and primates, several studies suggest it might also occur between humans and other animals, such as horses. It is often considered the foundation of empathy.

"In summary, our study reveals that horses can distinguish auditory and visual cues of human joy and sadness, as well as associate matching sound expressions with facial expressions. Horses showed a heightened interest and enthusiasm for happy expressions. Those interacting with horses could benefit from conveying joy in such interactions," concluded Jardat.

The researchers believe that further studies are necessary to better comprehend the accuracy of horses' perception of human sadness. In future endeavors, they aim to explore whether horses can differentiate sadness from other negative human emotions or whether human sad expressions influence equine behavior, particularly in human-horse interactions.