All silences are not equal, some seem quieter than others. Why? It’s all to do with the way our brains adapt to the world around us, as Tom Stafford explains
A “deafening silence” is a striking absence of noise, so profound that it seems to have its own quality. Objectively it is impossible for one silence to be any different from another. But the way we use the phrase hints at a psychological truth.
The secret to a deafening silence is the period of intense noise that comes immediately before it. When this ends, the lack of sound appears quieter than silence. This sensation, as your mind tries to figure out what your ears are reporting, is what leads us to call a silence deafening.
What is happening here is a result of a process called adaptation. It describes the moving baseline against which new stimuli are judged. The way the brain works is that any constant simulation is tuned out, allowing perception to focus on changes against this background, rather than absolute levels of stimulation. Turn your stereo up from four to five and it sounds louder, but as your memory of making the change rapidly fades, your mind adjusts and volume five becomes the new normal.
Adaptation doesn’t just happen for hearing. The brain networks that process all other forms of sensory information also pull the same trick. Why can’t you see the stars during the daytime? They are still there, right? You can’t see them because your visual system has adapted to the light levels from the sun, making the tiny variation in light that a star makes against the background of deep space invisible. Only after dark does your visual system adapt to a baseline at which the light difference created by a star is meaningful.
Just as adaption applies across different senses, so too does the after-effect, the phenomenon that follows it. Once the constant stimulation your brain has adapted to stops, there is a short period when new stimuli appear distorted in the opposite way from the stimulus you’ve just been experiencing. A favourite example is the waterfall illusion. If you stare at a waterfall (here’s one) for half a minute and then look away, stationary objects will appear to flow upwards. You can even pause a video and experience the illusion of the waterfall going into reverse.
It’s a phenomenon called the motion after effect. You can get them for colour perception or for just lightness-darkness (which is why you sometimes see dark spots after you’ve looked at the sun or a camera flash).
After-effects also apply to hearing, which explains why a truly deafening silence comes immediately after the brain has become adapted to a high baseline of noise. We perceive this lack of sound as quieter than other silences for the same reason that the waterfall appears to suck itself upwards.
So while it is true that all silences are physically the same, perhaps Spinal Tap lead guitarist Nigel Tufnel was onto something with his amplifier dials that go up to 11. When it comes to the way we perceive volume, it is sometimes possible to drop below zero.
This was my BBC Future from last weekend. The original is here.
Mind Hacks 
Is this unique to humans? (If it’s even possible to know). Chronic noise in cities has been shown to change wild animal behavior. Those “happiness” studies mention that while humans have a set level of contentedness (after say a crippling accident), the one thing they say humans cannot adjust to us noise.
So I have to wonder if noise is an especilally destructive phenomenon. Amps on eleven non withstanding….
I also wonder about places with snowscapes. People refer to a “loud silence”. But the explanation there is that noises are louder when the ground is frozen.
That being said, in spite of the definition, “deafening silence is the period of intense noise that comes immediately before it,” there remains a marked q u a l i t y to the actual type of silence perceived depending on the environment the sound being made in is at, which changes the experience of silence.
In terms of acoustics and how sound behaves; the speed at which silence is truly acheived at the very cease of an intense noise would undoubtedly vary from an all glass auditorium to a wooden hall with carpeted flooring. As it is, even when the noise has ceased, sounds would continue to ‘bounce off the glass walls/windows’ for a slightly longer period than in a sound-proof recording studio where those same sounds would have been “absorbed” by carpeted grounds and proofed walls whereby, deafening silence can be felt almost immediately compared to the former environment.
As much as the term is widely used emotively, there are also situations where that experience can be sensed where no real intense noise is being made prior to the experience. In fact, the contrary! ..where sounds you’ve hardly ever noticed and usually desensitised from are being “heard”! Such as your own breath when wandering in a pitch-black abandoned mansion or when you’re in a library. So it is not merely psychological, where that term is being used but perhaps your brain is being aware that it is not completely an ordinary experience being in an environment so quiet that one had began to notice the sound their own breath, the very throbbing of your heartbeat or for the first time hear how their hair parts when slight wind is felt passing through them! Times like these, I think the material and confines of the setting that person is in has an affect of the sensitivity to that deafening experience – perhaps all that decorative tapestries by the walls and carpeting on the floor in that particular room have set the place to absorb the tiny bits o’ noises from its surrounding so well, that even if low decibel noises were made from adjacent rooms, they would not travel enough to disturb where you are the same way it would in your every other day setting ..and you sense that auditorially.
[There is also the instance where you could possibly just be in love and/or nervous when you hear that, of course, but–!]
I do know, however, one way to reverse the effect of “deafening silence”, and that is to heighten the sense by reducing the function for sight – blindfolding will surely give you back the notion and heightened sensitivity to “observe” sound once more if ever you wondered about in a silent library, surely the experience would become less deafeningly silent should you close your eyes for a moment and begin to take just a few steps as you’re at it.
Just make sure you’re not anywhere near the stairwell ;~}
[Btw – a sentence in the seventh paragraph says you’ve forgotten to place a between “for” and “colour”.
>> “You can get them forcolour perception or”]
Good piece, nonetheless; as usual.
**[Btw – a sentence in the seventh paragraph says you’ve forgotten to place a {space} between “for” and “colour”.
>> “You can get them forcolour perception or”]
@Iszie – thanks for the comments, and pointing out the typos
@amelie – yes, the quality of echos has a powerful effect on how a place sounds (or doesn’t), even when we don’t consciously perceive these echos (for more on this, see the Haas Effect – you can read about it in Mind Hacks books amongst other places)