Our most recognizable screams are the most joyful

Imagine that you’re sitting in a park on a summer day, and a toddler shrieks with joy as the sounds of an ice cream truck come down the street. Then, a few minutes later, the kid screams again, this time in rage: he’s just dropped the cone on the pavement. Which scream do you think will grab your attention faster?

Counterintuitively, it appears that it’s the happy scream, at least according to new research published in the journal PLOS Biology on Tuesday.

In our primate relatives, screams are used largely to signal threats: to warn of a predator, or summon allies to a territorial battle. Those screams need to get a response from their audience, and they need to get it fast. So researchers expected humans to be most attuned to “alarm screams.” Instead, the humans in the study appeared to process screams of joy faster, both in their conscious actions and in the activity of their brain.

To test how humans react, researchers first needed to develop a “taxonomy of screams.” They brought in 12 volunteers, and asked them to scream as they would in six different situations: fear, anger, pain, joy, sadness, and pleasure. Another group rated those screams on their alarm level, or “how urgently one needs to respond.” As the researchers expected, screams from situations of anger, fear, and pain all rated as more alarming.

[Related: Why you’re powerless to ignore a crying baby]

Then, they played different screams back-to-back for different volunteers, and asked them to identify the emotion behind the noise. What they found was surprising: people were much faster to recognize a scream of joy than fear or pain. That pattern held even when volunteers only needed to distinguish between alarm and non-alarm screams.

So they ran another experiment, hoping to see how people processed the different screams at a neurological level. This time, they asked people simply to guess the gender of a screamer—a question used as a misdirection, so that they could monitor a person’s brain waves as they paid close attention to the noise.

The results seemed to bolster the previous findings: across many auditory brain regions, “a lower, not a higher, alarm level of screams is able to elicit more activity,” the authors write.

That may be because screams of joy play a larger role in human society, and our attention has evolved accordingly, the authors write. But there are also explanations that could have less to do with innate biology, and more to do with our day-to-day experience. Other neuroscience research suggests that the human brain becomes better at processing and interpreting a stimulus—like a happy scream—as it encounters it repeatedly and places it in context. It’s possible that a group of university volunteers has more experience with screams of joy than those of fear.

And, of course, the communication between the screamer and listener could be in-part cultural. Screamers made noise based on how they expected to react in a situation, which could be shaped by a movie like Psycho, or the ubiquitous “Wilhelm scream.” The resulting noises weren’t exactly authentic. After all, in reality, our reactions rarely line up with clear emotional stereotypes.