Many vertebrate animals communicate effectively using sounds that convey their state of emotional arousal and valence (whether they are experiencing positive or negative emotions). If you have ever heard a pig scream, you will know that this sound is extremely efficient at expressing emotional distress. Is it possible that humans can understand the emotional content of sounds made by different species? Darwin himself described similarities between how humans and other animals express emotions, which leads to the possibility that there is a universal system of expressing emotional content within mammalian groups.
In a new study by researchers led by the University of Copenhagen, participants listened to sounds made by several different ungulate species and answered questions about what they perceived the emotional state of the animal to be. Although previous research has shown that humans can detect the level of emotional arousal (bodily activation), there is very little research on whether humans can interpret the valence of another mammal’s calls.
For the investigation, more than a thousand people from 48 different countries listened to the vocalizations made by individuals from six mammal species. The sounds of goats, cattle, Asian wild horses (Przewalski’s horses), domesticated horses, pigs and wild boars were played to participants online. This marks the first time that so many different animal sounds have been tested on humans, both in terms of arousal (i.e., stress/excitement).
The participants successfully identified the arousal states of the ungulate calls in 49 to 54 percent of cases. They were also able to identify the correct valence of the call, but there was a much larger variation in this variable between species (33–68 percent correct). These results were greater than would have been expected if the participants had simply made random guesses about the arousal state and valence associated with the animal’s call, indicating that humans are able, at least to some extent, to understand the emotional expressions of other mammals.
The researchers recorded the calls of test animals in various states of arousal, as assessed by the animal’s heart rate and body movement behavior. Each animal’s valence was also noted at the time that the call was made. For example, animals making calls while expecting to receive food were in a positive emotional state, whereas those experiencing food frustration made calls while in a negative emotional state. The emotional valence was also verified using behavioral indicators described in the research literature.
“Our results show that, based on its sounds, we humans can determine whether or not an animal is stressed (or excited), and whether it is expressing positive or negative emotions. This applies across a number of different mammals. We can also see that our ability to interpret the sounds depends on several factors, such as age, close knowledge of animals and, not least, how empathetic we are towards other people,” said study co-author Elodie Briefer.
Participants also gave details of their age, gender, occupation and level of education. They were asked whether they worked with animals of any sort and, just before completing the online process, were required to take an empathy test to assess the extent to which they understand and share the emotions of other humans.
The results, published in the journal Royal Society Open Science, showed that people who do well on human empathy tests are also measurably better at decoding the emotional sounds of animals. In addition, the ability to understand the emotional content of animal vocalizations is most developed in people who are between 20 and 29 years old, and in people who regularly work with animals. Thus, the results suggest that an intimate knowledge of animals generally promotes the understanding of animals’ emotional lives.
“It was really surprising for me and very interesting that those who performed well in a recognized test to assess people’s empathic level – towards other people, mind you – were also significantly better at understanding the emotional lives of animals,” said Briefer.
“We could have used other tests that measure how a person relates to animals, but to make it simpler, we stuck to this particular empathy test, which was translated and validated for the eight languages in the study. It is a recognized test, but it measures empathy towards other people. Nevertheless, we see a clear correlation with the ability to interpret animal sounds.”
“This is good news for animal welfare. For example, farmers who want to ensure that their pigs are thriving are well-equipped to capture that. Today, animal welfare is defined by the emotional life of animals. Therefore, new knowledge provided by this study is important for both basic and applied research. On the one hand, it increases the understanding of animal emotions, and it opens opportunities to improve that understanding.”
According to Briefer, the knowledge contributed by the study shows the path to concrete ways to work on improving animal welfare through an understanding of their emotional lives.
“For example, the development of an app where AI supports those who work with animals offers promising perspectives. But it is also important to note that there is nothing to prevent someone from beginning to improve their own skills now if they interact with animals on a daily basis,” Briefer points out.
“When students try the test in class, they obtain an average of 50 percent of correct answers on the first try. After we talk about the sounds and knowledge that we have about animal vocalizations, they improve. On their second attempts, they typically get above 70 percent correct. It is natural to explore this potential in future studies. I definitely think that it’s possible to practice and improve this ability for the vast majority of people,” said Briefer.
The researchers conclude that their results support the idea of a common emotional system between mammals, which may have been preserved throughout evolutionary history. They found that participants were able to recognize high and low arousal states in particular, but could also discern whether animals were experiencing positive or negative emotions at the time they made the vocalization.
According to Briefer, this may be because we in the mammalian family share common traits when it comes to how we express the intensity of our emotions (i.e., arousal), and these have been conserved throughout evolution. In contrast, the expression of emotional valence is more difficult to interpret and may not have been as highly conserved across species.
“Roughly speaking, higher-frequency sounds (in addition to other features) are often a sign of higher arousal, and lower-frequency sounds a sign of lower. If a subject uses the same standard to interpret animal sounds that he or she would use to understand a human, then it is often correct. We express arousal more similarly than valence because it is linked to stress pathways, which are evolutionarily well preserved in mammals.”
The researchers say that domestication may have played a role in the ability of humans to recognize and empathize with the emotions of animals. Their results show that humans are better able to recognize the emotional expressions of domesticated species than of wild species. However, they do acknowledge that more research is needed to test whether humans can perceive subtle differences in animal calls conveying information about emotional arousal and valence.
By Alison Bosman, Earth.com Staff Writer
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.