Is this woman screaming from fear or sexual delight?
Mammals often use screams as alarm signals, but humans also scream to communicate a variety of emotions, such as screaming with happiness or pleasure.
Animals typically produce a loud, piercing cry — a scream — as a survival mechanism in response to dangers in their environment. If a predator appears, an aggressive scream might scare-away the threat, for instance, whereas an alarm call can also serve as warning for other potential prey.
One study now claims that humans are more sensitive to screams prompted by less-scary scenarios.
According to research led by psychologists at the University of Zurich in Switzerland, people can distinguish between screams associated with a variety of feelings, not just negative ones like fear, but positive emotions like joy too.
The new study, published in the journal PLoS Biology, involved asking a dozen participants to vocalize several emotions. Another group of 23 participants then had their brains scanned inside a functional Magnetic Resonance Imaging (fMRI) machine while they listened to the screams and rated their emotional quality.
Results from the ratings were not controversial, showing that screams have different psycho-acoustic qualities that can be clustered into distinct types associated with six emotions: pain, fear and anger (alarm screams), and pleasure, sadness and joy (non-alarm screams).
Acoustic spectrograms of six distinct types of screams.
But the neuroimaging results led to a counter-intuitive conclusion: the brain seems to process and perceive alarm calls less efficiently than cries that don't signal danger.
As lead author Sascha Frühholz says, "Listeners responded more quickly and accurately, and with a higher neural sensitivity, to non-alarming and positive scream calls than to alarming screams."
It's important not to over-interpret results from comparing the response to various screams, however. As the methods state: "All participants were healthy humans with no acting experience, training in acting, or history of being professional actors."
The participants were asked to imagine the emotions they would feel in a specific scenario based on short, written instructions: an angry scream was prompted by the words 'You are being attacked by an armed stranger in a dark alley,' for instance, while pleasure came from simply reading 'You are screaming from sexual delight.'
The researchers describe the acted screams as "acoustically similar to natural screams." That doesn't mean they're the same, which presents the possibility that participants had subconsciously detected that they were listening to artificial screams. If they heard an audio recording of a genuine scream of terror from a real situation — such as someone being scared by a spider — it's possible a listener would have been more sensitive to that scream.
A woman scared of a spider.
A scream might also be processed faster if it's produced by a trained actor who makes it sound more realistic. For example, you would expect fake screams of 'sexual delight' from a porn star to be more convincing than those made by some random amateur who's participating in a scientific study.
For the sake of argument, assuming that the human brain does indeed process positive screams more efficiently than negative alarm calls, why would that be?
One explanation is that, compared to other primates, people live in more complex social environments, which forced our species to shift its cognitive priorities.
As Sascha Frühholz adds, "It's highly possible that only humans scream to signal positive emotions like great joy or pleasure. And unlike with alarm calls, positive screams have become increasingly important over time."
That interpretation reflects a common error in evolutionary psychology, which is that observations based on present-day humans represents what happened in the past. Like the idea that beards evolved to absorb punches, it's an attractive after-the-fact explanation with no evidence of evolution — known as a 'just-so' story.
So while the new study reveals that people can distinguish between different emotional screams, better tests would be needed to prove that humans really are more sensitive to an orgasmic scream than a potentially life-saving alarm call.
