You scream, I scream: Why you cannot scream yourself deaf

It emphasizes the post with a certain gravitas.  Source: Steve Wolf designs, 2016.

One day at the Central Park tennis courts in New York City, “Martha Stewart” posed an excellent question about grunting and it went something like this:

Martha: “I wonder why the grunting doesn’t affect the grunters.”

Me: “Uh, because it supposedly relaxes their muscles, allows them to focus and because… they’re the instigators?”

Martha: “OK but I mean… For example if you’re in a small room and you yell really loudly will that deafen you as much as the guy next to you?

Me: “I… Well players are in open space… Of course… Well, so what we know is… It’s just that… Ohmygoodnessi’mlateformythingstuff!!”

(run, run, run, run)

Rolling the boulder over the entrance of my cave, I calmed my frazzled nerves by meditating in solitude with my best friend Pub Med.  Some Illy, a lot of doughnuts and a fortnight later, I returned to Martha who was still waiting patiently at Central Park and calmly began to answer her question.

When you speak, there is the sound that reverberates back to you as well as the sound conduction going through your skull.  Since sound is received through your auditory processes via the vibrations of tiny bones in your ear and then later translated into sound by your brain, this situation can be interpreted as a double whammy for the player (i.e. it must be worse for Sharapova as opposed to the audience, as Sharapova has both the free soundwaves going into her ear canal as well as the soundwaves going through her own vibrating skull).

Side note: The skull conduction distorts the sound of your own voice as you perceive it and is the reason that you stare in horror at your cell phone wondering whether you really are the person you thought you were when it plays back the voice recording you just made.

But I digress, so let’s take a brief look from the perspective of the audience first, and then the player.  But please memorize this simplified graphic of the gross anatomy of the ear first.

Got it? Let’s proceed.

The audience has at least three readily available gross anatomical defenses against the shrieking incursion.

1 – Hear no evil.  Clap your hands over your ears.  Writhing or laughing off the pain is optional but may, scientifically speaking, also help take one’s mind off of the auditory pain.

Sir Chimp, one of our closest extant relatives shoving his fingers into his ears. Should you believe in that sort of evolutionary thing.

2 – The stapedius muscle.  Without going into ridiculous detail, this muscle of the middle ear reflexively attempts to quell the screeching emanating from Sharapova by regulating how much the stapes bone (also known as the “stirrup” bone because, well it looks like one) vibrates.  You can imagine this in the diagram below:

Zoomed in, with the soft tissue drawn in.  Note the tensor tympani and stapedius muscles and their sound-deadening actions with muscle contraction.

3 – The tensor tympani muscle.  This muscle (also of middle ear fame), is known to dampen the sounds of chewing.  Audience members in the front rows or box seats that are too autocratic to clap their hands to their ears might instead be gritting their teeth in anticipation of the shriek and this might allow the tensor tympani to decrease the amount of incoming shriek processed by the person via modulating the stiffness of the eardrum.

It’s more difficult to understand without a 3D model in front of you, but for you folks that like animations, take a look here for a cartoon that takes you deeper through the anatomy, and also goes into how sound transduction works.

But what about the poor players themselves?  Martha asks.

First, we know anecdotally that the Sharapova shriek has little immediate effect on Sharapova herself.  For example, I haven’t noticed her answering post-match press interview questions like: “So Maria, it looked like your services were averaging a few MPH higher than a few months ago.  How’s the shoulder feeling?” with: “WELL IF I HAD TO CHOOSE I THINK I WOULD BE TEAM EDWARD BECAUSE JACOB IS A LITTLE BIT TOO SHORT FOR ME.”

As it turns out, the stapedius muscle can also help to protect yourself from your own voice. While the tensor tympani muscle is suspect as well, it is not always used.  But what Sharapova has going for her that the audience members don’t, is the benefit of a specialized type of inhibitory neuronal activity known as corollary discharge – a way by which the body dampens a sensory response to an action it knows it is going to perform.

While the idea of corollary discharge has been around for well over a century, authors Poulet and Hedwig have more recently discovered the actual neuron involved during this fascinating phenomenon.  As seen in the humble cricket, their studies go a long way in explaining why Sharapova et al. have not yet succeeded in deafening themselves.

Crickets in case you didn’t know, chirp for love (among other things).  If a guy is feeling in the mood, he might sing his own version of Nat King Cole’s L-O-V-E in an attempt to attract a gal.  True to real life, sometimes his hard wrought efforts work in a New York minute and sometimes they culminate in him hopping/flying home chirping the cricket equivalent of The Miracles’ The Tracks of My Tears.

Although the Sharapova shriek is unlikely to be a mating call, both chirping and shrieking are nevertheless challenging auditory incursions over time and necessitate a method to protect one’s self from it – while being able to distinguish other sounds coming from the immediate environment.  It would be profoundly depressing if the guy cricket was amidst chirping a fascinating rhythm and was unable to hear the girl trying to harmonize over the sound of his own “voice” while he was slowly going deaf, right?

So when the cricket chirps or Sharapova’s caterwauling begins, their motor neurons send a corollary discharge to the corollary discharge interneurons which then transmit it to the sensory neurons, inhibiting the anticipated feedback sensation of the sensory neurons.  This dampens the reception to their own emitted sounds while simultaneously still allowing them to hear sound produced by something else close by.

So for all of you serious screamers out there, please take a moment to thank nature for maintaining and allowing you to concurrently use one of your five major senses.  Tennis is hard enough with the ability to hear and if you don’t believe me, try earplugs the next time you play…

Caveat: The homologous corollary discharge interneuron in humans to the best of my knowledge, has not yet been identified, but likely exists.

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