The Sound of Silence in the Brain

Isn't it interesting that you know what I'm talking about in the headline, and yet, the very definition of silence is that it doesn't have sound?

Hiya!

I don’t remember what I was reading or how old I was the first time I read that silence “rang” in a character’s ears, but it stuck with me. Perhaps it was the first time I associated silence with having a sound, whereas before, I associated it with having no sound at all. I remember searching for silence after reading that to see if I could hear the “silence ring” in my ears, but silence isn’t easy to find when you’re growing up in a family of six within a city.

Apparently, I’m not the only one who’s ever been curious about silence. Neuroscientists, it turns out, have many questions about how silence works in the brain and have searched for ways to study it — which is challenging, to say the least. Still, experts have two primary questions regarding how the brain processes silence. Do our brains “hear” silence like we can hear the birds chirping outside? Or is silence merely a place marker the brain inserts between sounds that we perceive as silence?

Both of these questions have one thing in common — perception. So, that’s what experts decided to focus on.

All Comes Down to Perception

Silence is a bit of a puzzle in many ways, but one mystery has nagged at psychologists and philosophers for a long time, and it has to do with how our sensory perception works. On the surface, our most basic senses — sight, sound, taste, touch, and smell — all seem self-explanatory. We see because of how light interacts with our eyes, we feel when something comes in contact with our body, and we hear when something nearby makes a sound. Right?

Well, it turns out, like so many things, it’s a bit more complicated than that. Co-author of the paper I’ll tell you about soon and an assistant professor of psychological and brain sciences at Johns Hopkins, Chaz Firestone, explains:

“Silence, whatever it is, is not a sound. It’s the absence of sound. And yet it often feels like we can hear it. If silence isn’t really a sound, and yet it turns out that we can hear it, then hearing is more than just sound.”

That seems almost like a riddle Alice might hear in Wonderland. While seemingly insignificant, the idea kinda twists the mind a bit. In a way, it reminds me of temperature — that cold doesn’t really exist but is merely the absence of heat. Of course, this, too, is an over-simplification. Still, the idea applies. If cold is the absence of heat, yet we still feel it, then perhaps silence is the absence of sound we hear.

The Study

Firestone and his colleagues at Johns Hopkins University wanted to test whether our brains actively perceive silence the same way they process sound. So, they conducted their study using tweaked, well-established auditory illusions commonly used by experimental psychologists. They published their research in the Proceedings of the National Academy of Sciences USA (PNAS) in July 2023.

To see how the mind reacts to silence, the researchers used three silence illusions to create seven silent experiments in which 1,000 people participated. (You can try them out yourself by clicking on that link.)

One illusion, named “One is More,” involves two short tones followed by a single longer tone. People often state that the single noise is longer than the two shorter ones combined, even though they are actually equal in length. This is because of a perceptual process called “event segmentation,” which is when the mind isolates continuous input into specific “events.”

Classifying each distinct sound as a single event makes it more challenging for the brain to combine two events and compare them to the third. In this case, combining the two distinct tones and comparing them to a longer tone. This often leads to the perceptual illusion that the longer sound is the longest.

The researchers took this well-known illusion and flipped it. So rather than hearing intermittent tones and otherwise having silence, the team exposed the participants to the sound of a busy train station or restaurant, then turned it off for two silent breaks separated by brief background noise, and then shut it off again for one longer interval of silence.

Another silent experiment, the “Oddball” illusion, immerses participants in a “soundscape” made of two distinct sounds: an engine rumbling and a high-pitched organ. Here were the instructions when I gave it a shot (the bolding is theirs):

“[Y]ou will hear five silences in which one of the two sounds goes silent. The first four silences will be identical (and equally long), while the fifth silence will be different. Is the fifth silence longer or shorter than each of the first four?”

The Results

Ultimately, the researchers found that their versions of the auditory illusions were as strong as the originals.

For the “One is More” illusion, the participants reported that the extended pause in the soundtrack was longer than the two combined shorter ones that were separated by a moment of noise. My results for the “Oddball” illusion matched the majority of the study participants — that the fifth silence sounded longer than the first four.

The participants’ brains also responded to the silence as they would to the sound illusions. Rui Zhe Goh is the paper's first author and a Ph.D. candidate at Johns Hopkins. He’s also the first doctoral student at Johns Hopkins to pursue a joint Ph.D. in philosophy and psychology. Goh states that the study’s results “suggest that our mind constructs similar auditory representations that might underpin our experience of silence.”

While research in this field is still new, this study suggests that silence is more than just the absence of sound. It’s something we actively perceive — just like noise.

Perspective Shift

For some reason or another, the idea of silence having sound stuck with me for the rest of my life after first reading the description of silence ringing. I was delighted the first time I heard it, though again, I don’t recall where I was or how much time had passed since reading the phrase. But I remember how magical it felt to “hear” silence, which I’ve listened for ever since.

Although the research we discussed today didn’t focus on any ringing associated with silence, it does inspire me to think that silence is its own enigma. While we may dismiss or overlook it, we also have a poetic, even personal relationship, with silence.

We seek silence when we become overwhelmed. Sometimes, we run from it, terrified of what thought might squirm into our consciousness to fill the soundless void. Silence can recharge us or become an endless abyss. Consider the 1965 song, The Sound of Silence, written by Paul Simon and sung by Simon and Garfunkel. When introducing it at a live performance, Garfunkel summarized the song’s meaning as:

"[T]he inability of people to communicate with each other, not particularly intentionally but especially emotionally, so what you see around you are people unable to love each other."

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Photo by Ernie A. Stephens on Unsplash