Shhhhh… Can You Hear That?

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For a long time, silence has been thought of as the mere absence of sound. But what if we can perceive silence, in the same way we perceive sounds?

We are constantly hearing sounds, all around us. When we hear sound—a question, a joke, a line of music—we don’t simply hear a random assortment of sound waves. Our brain parses through and separates the sound waves into discrete segments, allowing us to comprehend what we just heard. This process is known as auditory event segmentation.

So, we know that sounds are parsed and sorted into auditory segments. But what happens when there is silence? Does event segmentation simply turn off, or does our brain also segment silence in the same way it segments sound?

This question is exactly what Rui Zhe Goh, a PhD student in philosophy and psychology at Johns Hopkins University, researches under the mentorship of philosopher Ian Phillips and psychologist Chaz Firestone. To collect data, Goh and his team took a few previously tested auditory illusions and replaced the original sound illusion with silence. “We’re asking if silences also elicit a segmentation process. And to find that out, we ask whether these illusions that happen with sound also happen with silences,” Goh said.

In the first experiment, called “One-Silence-Is-More,” researchers played two different sound clips to their test subjects. The first clip consisted of one continuous silence, while the second clip contained two short silences. Both durations of silence were the same, yet the subjects perceived the one continuous silence to be longer than the two short silences. This was a promising result—the auditory illusion still worked, even with silence.

In the second experiment, the “Oddball Silences” illusion, Goh focused on the perception of partial silences. In other words, what happens when there are two sounds playing, and only one of them goes silent? It turns out that we perceive the lengths of these partial silences differently, depending on what the preceding partial silences were. “Different silences ‘sound’ different,” wrote Goh in his research paper, published in the Proceedings of the National Academy of Sciences (PNAS).

In the final set of experiments, “Silence-Based Warping,” subjects heard two tones played, with a pause between them. The first time the tones were played, there was complete silence. But in the second test, there was embedded silence—background noise played before and after the silence, that disappeared when the two tones were played. Subjects perceived the two tones to be farther apart when played in embedded silence than in complete silence, as would be expected if embedded silences were indeed segmented into auditory events. This illusion confirmed for Goh and the other researchers that our brain can perceive silence as it does sound, segmenting it for interpretation. “It’s a bit counterintuitive to think perception can retrieve what’s not there. But even when there is no sound out there in the world, we can still get a perceptual experience,” Goh said.

For Goh, philosophy and silence are deeply intertwined. What began as a philosophical question about whether silence is perceived led to his scientific experiment, and ended with empirical evidence that demonstrates silence can be heard, not just inferred. Moving forward, Goh is excited to tackle other philosophical questions through a scientific lens, continuing to expand our framework of perception.