科学美国人60秒:Screams Heard Round the Animal World

What does panic sound like? <<clip of Homer Simpson scream>> Like that, for sure. But also like this <<pig sound>>. And this <<chickadee sound>>. But maybe you already knew that. Because a new study shows that humans are actually good at identifying vocalizations that are emotionally intense…even when those outcries come from other species. The findings are communicated in the Proceedings of the Royal Society B.

[Piera Filippi et al., Humans recognize emotional arousal in vocalizations across all classes of terrestrial vertebrates: evidence for acoustic universals]

It was Charles Darwin who first mused about the evolution of emotional expression. 

As he wrote in the Descent of Man: 

"All the air-breathing Vertebrata necessarily possess an apparatus for inhaling and expelling air.... When the primeval members of this class were strongly excited and their muscles violently contracted, purposeless sounds would almost certainly have been produced."

Now, if producing those seemingly purposeless noises turned out to be beneficial…by warning others of predators, summoning protection, or enticing a mate…the behavior would persist and, over time, become selected for.

Of course, for that to happen, the meanings behind those utterances would have to be clearly understood. To explore this question, researchers asked 75 volunteers to listen to vocalizations produced by nine different species, from black-capped chickadees to American alligators. The recordings included sounds made by animals when they were relatively relaxed…like this hourglass tree frog <<clip low arousal>>…or in some way excited…say, reacting to an aggressor or competing for a mate, like this hourglass tree frog <<clip high arousal>>. 

The listeners were then asked to identify which of the paired recordings from each species represented a sound of distress or “emotional arousal.”

The result?

“We found that, yes, humans recognize higher levels of emotional intensity in species which span across all of these classes.”

Piera Filippi of the University of Aix-Marseille in France and the Max Planck Institute for Psycholinguistics in the Netherlands, who led the study.

“Interestingly, we did not find any effect of language background on the human’s accuracy.”

Participants who spoke English, German or Mandarin all did equally well at pointing out which chirps, squeals, and hoots were emotionally charged. They were also able to tell when actors speaking in Tamil, a language none of them had ever heard before, sounded upset.

“The finding thus suggests that humans’ ability to recognize higher levels of emotional intensity in animal vocalizations is biologically universal.”

The listeners seem to be tuning in on the higher frequency of alarm calls, the researchers say. These shifts in pitch are perhaps clearest in the vocalization of infants, such as the piglet <<pig sound high arousal>> used in this study. That suggests that we may be hardwired to recognize babies in distress. 

We’re not necessarily horse whisperers…but it seems we all feel for that little piggy when it goes <<pig sound>> to make its emotions known.

—Karen Hopkin