There’s something powerful about the sound of a scream. Whether it pierces the silence of an empty building or rings out through a crowded room, it forces you to stop what you’re doing and take note. It turns out there’s a scientific explanation for that. Our brains are hardwired to recognize the sound of a human scream as a distress signal so that we can respond accordingly. We talked to neuroscientist Luc Arnal about what particular sounds make a scream a scream and how he studies the brain circuits that interpret them.
Shane Hanlon: Hi, Vicky.
Vicky Thompson: Hi, Shane.
Shane Hanlon: What’s the scariest sound you can think of, or I guess what, I’m just trying to think of, I’ve been watching a lot of horror movies lately. There are a lot of screams in horror.
Vicky Thompson: Sure.
Shane Hanlon: Let’s go with that. So, when you hear a scream, or what do you think of or what do you feel, or do you have any memorable screaming moments?
Vicky Thompson: Screaming moments? So I haven’t done it in a long time, so I can’t promise that it’s still really great, and I can’t do it right now because I’m actually in the office. But I have a really amazing scary scream. How do I know?
Shane Hanlon: Yeah, what’s your, I need data, Vicky.
Vicky Thompson: Oh, shoot. Okay. Well you can call my mom, but also …
Shane Hanlon: Okay. Done.
Vicky Thompson: I have just always, anyway. So one Halloween when I was in high school, I guess, early high school, my dad picked me up from wherever I was and we spent the rest of the night just driving around town. And whenever we would see a group of teenagers, cool teenagers on the street, I would just scream bloody murder as we drove by. Not screaming anything particular, just screaming like I was being stabbed. And, it was so fun.
Shane Hanlon: You’re the Vicky who screamed wolf.
Vicky Thompson: It was so, so fun. It was actually, I feel like it was my dad’s idea to do this, because I had a good scream. It was really scary and startling and just like …
Shane Hanlon: Oh, my gosh.
Vicky Thompson: Yeah.
Shane Hanlon: I have no idea how I’m ever going to be able to hear this, but I shall someday.
Vicky Thompson: If I’m ever home alone, I’ll voice note you.
Shane Hanlon: Oh, my God, this is exactly what, this is everything I’ve ever wanted. Thank you so much, Vicky.
Science is fascinating, but don’t just take my word for it. Join us, as we hear stories from scientists or everyone. I’m Shane Hanlon.
Vicky Thompson: And, I’m Vicky Thompson.
Shane Hanlon: And this is, Third Pod from the Sun.
Well, okay, so we are talking about loud noises, in this case mostly screams, because it is a few days before Halloween. And so a producer, a first time producer, which is always very exciting, Andrew Saintsing is here to tell us about a researcher who is investigating how our brains process screams. Hi, Andrew.
Andrew Saintsin…: Hi, Shane.
Vicky Thompson: Okay, so what do you have for us, Andrew?
Andrew Saintsin…: Well, I thought it would be fun to celebrate Halloween with a podcast full of screams. So I reached out to a neuroscientist who’s been mapping out the way signals from these types of sounds travel through the brain.
Vicky Thompson: So is he trying to figure out how screams activate our fight or flight response, to get us out of or through dangerous situations?
Andrew Saintsin…: Well, it’s funny, I thought our conversation would focus a lot more on fear than it actually did. It turns out, the emotional response that screams create in us really stems from our empathy for other people. Our brains are hardwired to recognize screams as distress signals. So in a lot of cases we end up running towards them rather than away from them. But I’ll let our expert, Luc Arnal explain.
Shane Hanlon: That’s an almost pleasant take on a pretty unpleasant sound, but I am interested. So let’s get into it.
Luc Arnal: Hi, I’m Luc Arnal. I’m a neuroscientist in Paris. I’m working at the Institut de L’Audition, so the Hearing Institute at Institut Pasteur, which is a French institute for research. I’m working on how the brain perceives, processes sounds from vocalizations to complex music. And we are interested in understanding how these sounds trigger emotions and specific behaviors.
Andrew Saintsin…: And it turns out that you actually have spent a decent number of years looking into how screams affect the brain. Could you tell me a bit about how you became interested in screams?
Luc Arnal: So, it all started when actually I had a baby, and I found out that there is not much you can do against the screams, especially the baby screams. And I thought, it’s actually a really interesting thing because you don’t have to learn how to scream. This is the first thing you can do. You do actually, the first vocalization you do when you give birth, when you are born, is actually to screen. And this is also a sign of good health, of good pulmonary health. And this is something you don’t have to learn. It’s extremely important to be able to scream, for a baby. It’s a vital sort of communication. If you can’t scream, then you multiply your chances to not get help, and then it will be difficult to survive. So screaming is really a vital vocalization. And I think for that, it’s a very peculiar vocalization.
As a biological object, it’s a super interesting object. And people had not studied scream so much, in particular from a brain’s perspective. So this is why I got interested in it, when I was hearing my little baby screaming in the middle of the night and there was nothing I could do, but running to her and trying to take care of her. And that’s the only way to get help. That’s their best way to get help. And they actually use very strange sounds that we don’t find very often in nature. Seems to be sort of a niche, an agnostic niche that is preserved for these alarm sounds, that they use to grab our attention and to force us to take care of them.
Andrew Saintsin…: So, what does that mean? Can you tell me more about that?
Luc Arnal: So, when you hear a scream, it sounds a little rough. It sounds like there are some texture in it. And that was my main intuition when I heard these sounds. So they’re not only loud, they also use specific accuracy features that’s called roughness. The roughness is actually, very fast modulations of the intensity of the sound. So the intensity changes really fast, between 30 hertz and 150 hertz. So if you want to compare when I speak, the intensity of the sound changes every five times per second, so at five hertz. So that’s the rhythm, the syllabic rhythm when I speak. But in screams, it changes much, much faster, and it gives the impression of something that bombards or something that is extremely fast. Something like a strobe light in the auditory domain. So it gives you a sound like …
Then, we actually compared the intensity of this roughness in screams and in neutral voices. And we found that screams were actually using this feature much, much more. And then we started to play around with roughness, and we tested how it changed the behavior. So we asked participants to rate how much the scream was unpleasant, for instance, on a scale from one to five. And we found that the screams that were the rougher were rated as the worst. So roughness was really predictive of how aversive the sound is. So this specific parameter was predictive of aversion. And then we also asked, we did an experiment where we were presenting screams on the left or the right. On the left or the right ear of the participants, and we asked them to detect whether it was on the left or the right. And we found that if the sound was containing roughness in it, the participants were much faster at detecting whether it was in the left or the right.
So, roughness also accelerates the behavior. So that’s very convenient, especially for babies. Because if they use roughness, then they can accelerate their parents’ reactions. So that’s what they want. They want to grab our attention, but they also want us to react as fast as possible. So it’s really a super interesting trick that they use and they tend to overuse it, but we don’t have its weight to that. So it’s unbearable, and you can’t get used to it. So that’s a very interesting thing because in general neuroscience, when you play a sound once, the second time you play it, you have reduced responses in the brain. The brain habituates, right? It’s not the case for screams. So they are immune to habituation, which is again a very interesting trick, for the purpose of alarming and getting attention and care.
Andrew Saintsin…: And so, it kind of is an alarm signal for the baby to get you to do something for them. But screams tend to, like you mentioned, the aversive reaction to screams and somebody might run from a scream. So I guess, I’m wondering how we deal with the fact that screams could both signal us that we need to get away, versus we need to go help someone?
Luc Arnal: The most important parameter to react to a sound is the intensity. If a sound is really loud, then would have a very fast reaction. You would have startled reactions, that we have very low reflexes that allow us to react extremely fast to loud sounds, for instance. But then, so intensity is interesting and it informs you about the distance to the source of the sound. So that’s a useful parameter, but you could have something that’s intense and that’s far away. So it’s a little under specified, it’s not really precise enough. Roughness really tells you whether the speaker, the emitter is really in pain, for instance, or these kind of things.
And so, it’s a much more informative kind of stimulus which says, “I want to be salient.” But then, you have to make a decision. What’s interesting with roughness, and we’re going to talk about the brain circuits afterwards, what’s interesting with roughness is that it’s salient and they actually reach, that actually targets a network in the brain that’s called the salience network, that has to do with arousal, attention, and also with sleep at night. So what this sounds to, is that they want to arouse you, they want to wake you up. That’s the goal. And then, you will make the right decision, depending on the context.
Andrew Saintsin…: How do you look at brain circuits? I’m just interested to know, what your approach to researching the brain is?
Luc Arnal: So, we use different methods of neuroimaging. So we have different kinds of approaches. The first approach that we have used was, the first method was FMRI, so functional MRI, magnetic resonance imaging. And that method allows you to see how much neurons consume energy in different parts of the brain. So basically, you have a map of the brain and you see which parts of the brain consume energy, depending on the stimulus. When we use that with screams, we found that of course the auditory system, the classical auditory system was actually activated by the screams. But not only the auditory system, we also found subcortical regions that belong to the limbic system, which is the system that deals with emotions.
So that was with FMRI, and it was a way to localize the populations, the younger populations that respond to screams. But, it was just part of the story. And then because FMRI is a relatively slow technique to measure brain activity, we turn to another technique which actually uses electrodes to directly measure the electric activity. The neurons are talking to each other, using electric activity.
So this is the electroencephalographic measurements method, but usually electroencephalography, EEG, is measured from the surface of the brain. So that’s not great, because we cannot know exactly where it is in brain. We can only see the electrical activity at the top of the scalp. So we actually decided to do experiments with patients at the hospital who are in a very peculiar situation. So these are epileptic patients, who have pharmaco resistant epilepsy. And so with them, the treatments, the pharmaceutical treatment doesn’t work and they have to have a surgery of the brain, to potentially remove the part of the brain that triggers the epileptic activity. And they spend two weeks in the hospital in observation with electrodes inside their brain, to sort of look at where the epileptic activity exactly comes from. And so during that period, we can actually do experiments with them, if they’re willing to do it with us.
And this is great, because we have access therapy to the brain responses inside the brain. So thanks to this method, we have recorded brain responses to sounds that look like screams, sort of synthetic screams with, I think probably 12 patients, who were patient enough to endure these sounds. But it was not playing too loud, we were playing it not too loud. And so we played these sounds that are click trains, that sound more or less like screams. And we wanted to look at this roughness parameter and compare it to pitch. And we found that whereas pitch was encoded in the classical auditory region, so the auditor cortex, let’s say, what we found is that roughness triggered a synchronization of populations of neurons, all over the brain in a lot of different regions.
And it was really spectacular because what this sounds trigger is a sustained response. So response that does … So that usually response goes up and down when you play a sound, regardless of the duration of the sound. In the case of rough sounds, of screams for instance, or synthetic screams, you play the sound and then the brain responses up during the duration of the sound. So it means that these sounds, they really bombard the system in a way that trigger synchronization, sustained synchronization of these populations in the brain, these neuronal populations. And this means that during a scream, there’s not much you can do. You cannot process anything else, right? Because it’s bombarding the system, you cannot process something else. You cannot do something else. So if you’re cooking and your baby screams, you’re going to have to stop cooking at some point, because it really drives responses down so strong that there’s nothing else you can do then. Go and take care of this sound, to make it stop.
Shane Hanlon: So what I’m hearing is that screaming can be a really effective strategy, if somebody is doing something you don’t want them to be doing.
Vicky Thompson: Yeah. But does it just work on people? Would it be a good way to get my dog to stop eating something that I don’t want them to be eating?
Andrew Saintsin…: It seems like it would work just as well on a dog as it would on a person. It turns out screaming evolved long before humans did.
Luc Arnal: It happens that almost every animal, at least mammals, and even beyond, use roughness as an alarm signal. And that’s really an interesting idea, because they are not … So in our vocalizations usually, we tend to exploit different niches. So we don’t want to use the same niches as whales, for instance. Or it depends of course on the size of the vocal tracts, but it depends also on how you express your ecosystem. And we don’t want to use exactly the same sounds, otherwise there will be interference between animals. But in that case, it seems that we all use the same to alarm, to warn. It seems that we all use the same feature, that’s roughness.
Andrew Saintsin…: The salience network, I’m so interested in that. Has that been known or, so you were saying it’s kind of, a lot of the details of it are being worked out still. So, how recently is this system been kind of identified and studied?
Luc Arnal: It’s actually a complicated system because in my view, it starts in a region that has been identified in the ’50s and the ’60s. But it’s really a diffuse system, as compared to more recent sort of systems like the auditory system. So this system seems to be more diffused, less clear when we look into the brain, and they are not very clear nuclei to look for. And it’s also diffused in a way that it goes almost everywhere. And so it’s, there’s not much I can say about it because it seems very complicated. What we see though is that we observe responses to these sounds in regions such as the amygdala, the hippocampus, the insula. Regions that belong to the limbic system that deals with emotion, that deals with urgent reactions. And I think that’s what’s important here. But then there are lots of things that we really need to look at now.
So, the research is not easy because it’s really deep in the brain. And with FMRI, it’s slightly easier to look at what happens on the cortex. So more on the surface, but what’s really inside and really deep can be hardly accessible. It’s not accessible using electroencephalographic signals, unless you use these intracranial electrodes. But the deeper you go, the more dangerous it’s for the patients as well very often, because there are really vital nuclei in there that are extremely hard to record. And it can be contentious because it’s hardly accessible. So it remains, there are lots of mysteries in there and I think this is why this research is so fascinating.
Andrew Saintsin…: For sure. And I guess, another reason to collaborate with people who don’t study humans. Maybe it would be easier to access deeper parts of the brain.
Luc Arnal: Absolutely.
Well, another way to look into this stuff is that, so one of the hypothesis that, so this system plays a role in the sleep-wake cycles. What I thought is that, if the system passes by these nuclei, these regions of the brain, which decide whether you sleep or you wake up, then the brain should respond differently to roughness than to other sounds. And so, just because it’s fun, we have done an experiment with 12 participants, where they were spending the whole night in the lab. And so, we were recording their brain activity while playing these screams at the very low level. And what we found is that, we found more or less the same effect, is that the encoding of roughness is preserved during sleep. So if you play rough sounds, if you play screams, you will have more reliable responses than if you play just a neutral vocalization.
And I think this speaks to the idea that these sounds should be more salience, and as they are more salience, they trigger, they tend to wake the brain more easily, just by triggering responses in these specific networks. But this is, again, very hypothetical, because during these experiments we were just recording scalp. The activity from the scalp using electrode, not inside the brain at the time. But these are hints that if it interacts with systems that regulate sleep, then it’s a good sign that it goes through the systems that I was talking about, the kind of systems that control arousal and wakefulness
Andrew Saintsin…: Thinking about sleep makes me think about alarm. Wake up, or alarm signals to wake you up. So are a lot of sounds that we have made in our environment, like fire alarms, things like that, are they taking advantage of this roughness?
Luc Arnal: Yes, absolutely. So that’s something we did test as well, was that when I was hearing fire alarms, I had the impression that there was roughness in it. And so we tested, we compared, we matched alarm sounds with instrument sounds, which were more pure. And we looked at again, this roughness and we found that indeed, alarm sounds exploit these roughness attributes. And again, it makes sense because it grabs attention, right?
But what’s interesting is that I’ve not found any notice of that, any mention of that in the literature on alarm signals, before we started to look into that. And it seems that sound engineer were using roughness, they were adding roughness without really knowing that it was useful. So it was purely intuitive on their path that they should be using roughness to warn people. And a lot of the buzzers, so the buzzers of the alarm clocks, the fire alarms, et cetera, they’re all super rough. And it’s interesting that it matches the features that we use when we want to warn people, using our voices.
Vicky Thompson: Okay. So that’s interesting and all, but I thought this was a Halloween episode?
Shane Hanlon: Yeah. All right, so what does this all mean for horror movies?
Andrew Saintsin…: Well, Luc says, “Horror movies often take advantage of our brain’s response to screams for jump scares. But really, keeping us on the edge of our seats requires a little more craft.”
Luc Arnal: If you want to scare someone, you can use these attributes and play really loud sounds, and use roughness if you want. And that would be startling, let’s say. But what people use in movies is tension. So instead of just playing it randomly at the moment you don’t expect it, they make you expect it. So they introduce this expectation. This expectation creates some sort of an anxiety about what’s going to come, right? And you can figure that something bad’s going to happen, and when it comes, you’re actually really surprised anyways. So the idea is to play on the prediction first and then on the surprise, and then you can maximize the reactions of people. But if you just play it without expectations, then there is no tension before and I think it’s less scary. So, the fear is really about expectations, right?
Andrew Saintsin…: Have you looked at or has anyone looked at the idea of, get the same scream sound when you’re in that space of you’re alone, and it’s dark and you’re scared, versus it’s just kind of, you’re out and about and someone screams. And I mean, I guess it would still be startling though, if you’re out in the middle of the city and someone screams. So, yeah. Have you looked scientifically at that or has anyone?
Luc Arnal: I don’t really know. So I told you that there is no habituation to screams, but in a way, the context is going to change the way you process screams. And sometimes we like to play with our emotions. We like to play, we like to listen to music that can be rough, such as metal or that kind of music. Some people appreciate that. We also like to play with our fears, when we go to the movies together and with horror movies. We like to hear roughness in stadiums. Everyone is screaming and still it’s really, it’s arousing. So it’s not fearful. It depends.
The emotional outcome also depends on the context in which it happens. So in stadium, you have expectations that, you don’t have expectations that people are screaming at you because they are not predators, I mean, not supposed to be predators in there. Yes, there are situations where we can stream and it’s safe. But I can tell you that when we started doing the experiment and I was recording screams in the lab at NYU, at the time, people who were behind the doors, wanting to call the police because they didn’t have the context, and so be where something really wrong is happening. But if you give them the context, then it was fine. It’s fine. So it changed, it really depends on the context in the end, it’s true. But it’s never really pleasant to hear someone screaming, I think.
Andrew Saintsin…: Yeah.
Luc Arnal: In very specific situations maybe. Anyways.
Andrew Saintsin…: Did you listen to the Wilhelm Scream?
Luc Arnal: Yeah, I’ve discussed the William Scream many times before, because every year I do have an interview before Halloween, so I have discussed that. The Wilhelm, yeah, I don’t don’t know exactly about this story, how they picked that scream and why they always use this one, because it’s ridiculous and makes me laugh every time I can hear it. I hear it in this, so yeah, I don’t know. It’s not that rough also.
Andrew Saintsin…: Yeah. So is it not a good scream because it’s kind of, you think it doesn’t have that roughness, or it maybe isn’t as intense as it needs to be?
Luc Arnal: I don’t know. It seems like overplayed. It seems like fake to me, and it’s not super easy to make a scream that sounds natural. So you really have to ask people to scream as loud as possible to make it sound natural. Otherwise, if people are shy, then it sounds faked. Yeah, and I think this one, I don’t know, it’s not really well done.
Andrew Saintsin…: Is that because, I don’t know if you think much about the production of the sound, but is that just because we don’t really get that roughness in our voices until we reach our max volume?
Luc Arnal: I think it’s both. So, when you don’t scream loud, you tend to over control what’s going on and then you can hear it. I mean, the control of vocal cords in that regime is not really perfect. So if you don’t put, it’s not like, we’re not expert at screaming, right? We’re just screamers. We can scream. If we do it really loud and we believe in it, then it’s going to work. If you try to control it, it’s very easy to feel that it’s a fake one. I mean, it depends on the speaker, some are better. You can train.
The people who are screaming in bands, they have very advanced techniques and they can also scream as much as they want for a really long time. Usually the vocal cords, which end up, I mean it’s a little bit dangerous for the vocal cord to scream. You cannot scream too much. But apparently with training, it’s okay, but you can lose your voice very easily. And that’s an interesting thing, because it’s a little bit about, it reminds me of the boy who cried wolf. If you scream all the time, people won’t believe in you. So it could be an adaptive situation, that we cannot scream all the time.
Shane Hanlon: Vicky, can you imagine if we were able to, well, I guess we are physically able, but if it was acceptable to scream all the time, what would this podcast be like?
Vicky Thompson: It would be much more like a grind core podcast, I feel like. But I would love it. I would feel so much more calm. I feel like ultimately, if we could just scream whenever we wanted.
Shane Hanlon: Well, so yeah, I will say, I am childless, but sometimes I look at kids who are just crying so hard about something whose stakes are so small, and I wish that that was just more, or at all socially acceptable.
Vicky Thompson: Yeah, to just sit down on the floor and scream and cry.
Shane Hanlon: That sounds wonderful.
Vicky Thompson: Like in my cubicle.
Shane Hanlon: I mean, that is the thing about us mostly working from home, because dude, who knows, maybe I do that and just no one knows. I turn off, I get off to this interview today and I’m just like, I need a moment for me.
Vicky Thompson: I’m just imagining if somebody puts their microphone on mute, and then you could just see that they’re screaming.
Shane Hanlon: That’s actually why I built an audio studio in my basement. It wasn’t for the podcast, for the musical instruments or any of that stuff. It’s just so that no one will, this is going in a-
Vicky Thompson: No one can hear you scream, back to Halloween.
Shane Hanlon: This is in a weird direction. Okay, so before we go down this rabbit hole any further, let’s just end it there. And so with that, that is all from Third Pod from the Sun.
Vicky Thompson: Thanks so much to Andrew for bringing us this story, and to Luc for sharing his work with us.
Shane Hanlon: This episode was produced by Andrew, with audio engineering from Colin Warren and artwork by Jay Steiner.
Vicky Thompson: We’d love to hear your thoughts on the podcast, so please rate and review us, and you can find new episodes on your favorite podcasting app or at thirdpodfromthesun.com.
Shane Hanlon: Thanks all, and we’ll see you next week.
All right, folks, this is a little different, because IM addressing you all directly in a stinger, but I got Vicky to record her aforementioned scream, so I wanted to give you a warning of that before we just get into it. So fair warning, here it comes.