Understanding animal emotions

Understanding other people's emotions plays a fundamental part in our ability to communicate. But does this extend to animals? Can you tell when a crocodile, frog or chicken is in distress? A new study from the Planck Institut in the Netherlands suggests that we all have some ability to sound out stress in other species. Their findings indicate that humans mainly rely on specific tones that indicate agitation, called emotional arousal. Lead author, Piera Fillipi, explained to Izzie Clarke, how it worked…

Piera - The emotional arousal is the level of responsiveness to external stimulation. This might range from very subdued to highly excited. So, for instance, right now you hear my voice, it’s quite relaxed, there are no dangers around me you might infer from my voice. But if I start talking in a more agitated way you might infer that there’s something around me that is disturbing me. And this is something quite clear we can infer from the voice of humans as well as of other animals it turns out.

Izzie - How did you investigate this?

Piera - There were basically two main questions. The first question was simply whether humans are able to recognise levels of emotional intensity or arousal in animal calls or animal vocalisations. If so, we wanted to see whether that is a biologically rooted ability or instinct, so to speak, or whether it’s driven by the cultural background or the language that the given human speaks. Maybe there are some language speakers that are more sensitive to sound motivation than other language speakers.

We included three different groups, so we had native speakers of English, of German, and Mandarin which is tonal language. And it turned out across all of these languages humans perform equally good in recognising the emotional intensity in animal vocalisations. This suggests that this is an ability that is actually biologically universal so it isn’t only the given language that humans speak.

Izzie - To test this, Piera and the team played two calls from a range of animals. One of the sounds displayed a high level of emotional arousal, say when an animal was agitated, and another when it was calmer with a low level of emotional arousal. All the participants had to do was choose which of the two sounds was the agitated signal.

Piera - I found that humans are particularly good in recognising higher level emotional intensity in animal vocalisations. To do so they rely on certain acoustic features in their calls, particularly on the acoustic features that I related to the tone of voice, and this applies across all of the species we included in our study. So tonal voice, the way we modulate our voice, is crucial in expressing emotions and it is crucial in perceiving and recognising the emotional content across all of these species. These species span from little frogs, alligators, up to Barbary Macaques and humans.

Izzie - The reason why we’re able to recognise these signals is still being explored with further research looking into frequencies of these noises, and whether it might even work in reverse. Can animals actually recognise when humans are agitated? And looking to the future, these findings could help improve artificial intelligence...

Piera - This finding can be applied in progressing technology for emotional expression and recognition in something that sounds quite cold, so to speak, which is artificial speech like speech that is synthesized artificially. I think that it would be a good idea to integrate what we know from findings on actual animal vocalisations that are emotional and apply that to emotional expression in synthesized speech.