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Why is the brain disturbed by harsh sounds?
Why do the harsh sounds emitted by alarms or human shrieks grab our attention? What is going on in the brain when it detects these frequencies? Neuroscientists from the University of Geneva (UNIGE) and Geneva University Hospitals (HUG), Switzerland, have been analysing how people react when they listen to a range of different sounds, the aim being to establish the extent to which repetitive sound frequencies are considered unpleasant. The scientists also studied the areas inside the brain that were stimulated when listening to these frequencies. Surprisingly, their results -- which are published in Nature Communications -- showed not only that the conventional sound-processing circuit is activated but also that the cortical and sub-cortical areas involved in the processing of salience and aversion are also solicited. This is a first, and it explains why the brain goes into a state of alert on hearing this type of sound.
Alarm sounds, whether artificial (such as a car horn) or natural (human screams), are characterised by repetitive sound fluctuations, which are usually situated in frequencies of between 40 and 80 Hz. But why were these frequencies selected to signal danger? And what happens in the brain to hold our attention to such an extent? Researchers from UNIGE and HUG played repetitive sounds of between 0 and 250 Hz to 16 participants closer and closer together in order to define the frequencies that the brain finds unbearable. "We then asked participants when they perceived the sounds as being rough (distinct from each other) and when they perceived them as smooth (forming one continuous and single sound)," explains Luc Arnal, a researcher in the Department of Basic Neurosciences in UNIGE's Faculty of Medicine.
Based on the responses of participants, the scientists were able to establish that the upper limit of sound roughness is around 130 Hz. "Above this limit," continues Arnal, "the frequencies are heard as forming only one continuous sound." But why does the brain judge rough sounds to be unpleasant? In an attempt to answer this question, the neuroscientists asked participants to listen to different frequencies, which they had to classify on a scale of 1 to 5, 1 being bearable and 5 unbearable. "The sounds considered intolerable were mainly between 40 and 80 Hz, i.e. in the range of frequencies used by alarms and human screams, including those of a baby," says Arnal. Since these sounds are perceptible from a distance, unlike a visual stimulus, it is crucial that attention can be captured from a survival perspective. "That's why alarms use these rapid repetitive frequencies to maximise the chances that they are detected and gain our attention," says the researcher. In fact, when the repetitions are spaced less than about 25 milliseconds apart, the brain cannot anticipate them and therefore suppress them. It is constantly on alert and attentive to the stimulus.
Luc H. Arnal, Andreas Kleinschmidt, Laurent Spinelli, Anne-Lise Giraud, Pierre Mégevand. The rough sound of salience enhances aversion through neural synchronisation. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-11626-7
(Score: 4, Informative) by Bot on Tuesday September 24 2019, @11:54AM (4 children)
In case you are wondering, the frequencies listed in TFS refer not to the basic frequency of the sound oscillation, but to its amplitude modulation freq.
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(Score: 2) by Rupert Pupnick on Tuesday September 24 2019, @01:05PM
Yeah, if you read TFA and look at the little pictures representing "smooth" and "rough" sounds, you get the impression there's some kind of AM going on. When I read the body of article, though, I don't see any clear description of what the sounds are like: are they pure tones (probably not)? do they have harmonics? do they have intermods (i.e. AM)? How about a spectral plot? Plus I don't think researchers started at 0 Hz at the low end of the test. Shabby science writing.
(Score: 2) by RamiK on Tuesday September 24 2019, @01:51PM
Reference: 20Hz = 1200bpm = https://www.youtube.com/watch?v=3eRA90rMq4A [youtube.com]
compiling...
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @03:41PM
Thank you for that!
I was confused.
(Score: 2) by All Your Lawn Are Belong To Us on Tuesday September 24 2019, @06:07PM
Thank you! Don't have time to RTFA and that was confusing.
This sig for rent.
(Score: 3, Interesting) by ilsa on Tuesday September 24 2019, @12:03PM (7 children)
I wonder if that's the key bit right there. We've evolved to respond immediately and urgently to when a baby cries, so it makes sense that any sound that mimics that cry would trigger the same alert response.
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @12:21PM (2 children)
Could it be that our babies evolved to emit the frequencies we are much likely to respond? Or maybe, just maybe, both sides evolved to get alerted at the sound of cats, big cats.
You know, correlation... causation... the kinda stuff that is usually modded Insightful even when it's unadulterated bullshit (large grin)
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @01:25PM (1 child)
When my wife starts bitching, everyone runs away.
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @06:30PM
Your right hand starts bitching?
(Score: 2) by DannyB on Tuesday September 24 2019, @02:39PM (1 child)
Similarly we're evolved to respond to hearing a child or an adult scream. It is a danger signal.
The human species will soon enough evolve advertising blindness and instinctive fight or flight response to the word Microsoft.
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(Score: 2) by ilsa on Tuesday September 24 2019, @10:29PM
*raises hand* Apparently I'm a pokemon cause I've already evolved both of those!
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @06:55PM
My mom's cat does a /really/ good baby cry when it's hungry. I think they let him watch too much TV.
(Score: 2) by inertnet on Tuesday September 24 2019, @07:36PM
I thought it had long been established that human alarm sounds put people on alert, because they're remnants of a pre-human warning system for predators. Apes and monkeys use similar types of screams to warn the group.
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @01:32PM (1 child)
Because we have ears. If we couldn't hear, we wouldn't be affected, would we?
What a dumb headline.
(Score: 2) by DannyB on Tuesday September 24 2019, @02:40PM
If you have ears, you aren't (most people aren't) affected in that way by hearing Beethoven. (and he was deaf)
But what about Justin Bieber music? (and he is not deaf)
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(Score: 2, Interesting) by CheesyMoo on Tuesday September 24 2019, @03:41PM (1 child)
"Our findings also have interesting implications for the understanding of acoustic communication. Producing salient auditory features to catch the attention of others is a primordial purpose of vocal communication. Here, we validate the hypothesis that temporally enriching sounds—in the roughness range—amplifies sensory salience and improves neural and behavioural efficiency. This finding connects with the recent observation that roughness is exploited in natural and artificial alarm signals as a privileged acoustic niche to warn conspecifics."
Clearing one's throat is a "rough" and valid way to get your conspecifics attention!
(Score: 0) by Anonymous Coward on Tuesday September 24 2019, @05:04PM
It wasn't just the headline, then. The whole damn "research" is garbage.
(Score: 2) by Bot on Wednesday September 25 2019, @07:50AM
And emitting is encoding.
Where does an alarm come from? A meatbag in distress, which will instinctively try to maximize the volume, even if only as a way to vent frustration. As with other sound systems, pushing the volume generates distortion. Which is good because other alarming sounds like a branch about to give in are distorted.
Smooth sound is easier to spectrally analyse, harsh sound is challenging. The challenge might be stimulating or unwelcome depending on the situation.
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