Perceiving Silence: A Response to Auditory Expectations and Brain Interpretation
Is the absence of sound perceived in the same way our brain processes auditory stimuli? This is a question that author Bethany Brookshire explores in her New York Times article “Silence is a ‘Sound’ You Hear, Study Suggests” (Brookshire, 2023). In this article, Brookshire examines a study published in the Proceedings of the National Academy of Sciences by researchers at Johns Hopkins University (JHU) titled “The perception of silence” (Pressnitzer & McDermott, 2023). The impetus of the study objective was driven by two main theories regarding silence. The first theory is that silence is something that is perceived, meaning we can literally hear silence. The second theory is that silence is something that is cognitively inferred or judged. Scientists designed an empirical study at JHU to make a conclusion regarding this long-standing philosophical debate. Through a series of seven tests, the scientists evaluate the impact of three types of auditory illusions.
The first type of auditory illusion explored is called the “one-silence-is-more” illusion (Pressnitzer & McDermott, 2023). In usual sound-based trials, subjects would be exposed to two tones versus one long tone to determine if the long tone is perceived as longer than the combination of the two tones. In this trial, the test aims to examine if the presence of two pauses between ambient sounds is perceived differently than one long pause between ambient sounds. In the second trial to evaluate this illusion, researchers had the subject evaluate the perceived length of the silences for both the two-pause silences and the one long tone silence. Subjects would then hold down a key to reproduce the duration of the pauses between ambient noises. In the third trial to evaluate this illusion, researchers introduced a “silence occlusion” (Pressnitzer & McDermott, 2023). This means that they included an additional sound that was played over the continuous silence (e.g. a bird chirping). In all three trials, the results showed a level of reproducibility to show that subjects perceived one long pause between ambient noise as longer than the two short pauses equivalent to the length of the one long pause, even in presence of additional sounds beyond the ambient (Pressnitzer & McDermott, 2023).
This series of trials reminded me of the experience I have when I use noise-cancelling headphones (one “pod” in each ear) while riding public transportation. During busy hours, the ambience between motor sounds and other passengers talking can be overwhelming. When one pod in each ear is applied, the sound is muted, in a similar way the three trials were conducted. Sometimes, when shifting of my location on the bus or train occurs, the pod can be shifted as well, allowing the ambient noise to be perceived again. In short bursts, or brief pauses, I don’t perceive the collection of pauses as silence. However, when the pods remain in my ear for an extended period of time, I do think of that as truly “noise cancelling”. This similar experience leads me to the same conclusion of the researchers where the length of silence can be perceived in the same way that sound is perceived.
The second type of auditory illusion explored by the researchers is called “silence-based warping” (Pressnitzer & McDermott, 2023). This is based on the phenomena of object-based warping, where people perceive the duration between two points as longer when embedded in a larger space or figure versus (such as a rectangle) than two points of the same distance that is not imbedded (such as two dots on a blank piece of paper). To test this with silence, the first trial to measure this illusion required subjects to perceive the time between two tones played. The first test in this trial was two tones played with no ambient noise and complete silence. The second test in this trial was playing the same two tones, with the same length between them as the first trial, with ambient noise in the background prior to the first tone and after the second tone, with silence in between the two tones. Subjects perceived the duration of the silence between tones during the embedded-silence ambient test phase as longer than silence between tones without the ambient noise (Pressnitzer & McDermott, 2023). The second trial to test silence-based warping was the same trial structure, plus an addition of a burst of white noise during the embedded-silence ambient phase to test for the influence of surprise. The results from this test proved that subjects still perceive sound between tones as longer during the complete silence phase (Pressnitzer & McDermott, 2023). The final trial to test silence-based warping was the same structure, but subjects were to assess the length between the tones after the complete silence phase while listening to ambient noise. The results from this test proved that conditions during evaluation of sound did not affect the primary results that human perception treats silence like an auditory process (Pressnitzer & McDermott, 2023).
Given this research, an example I can relate to is being in a class setting during an exam which is normally quiet. The professor will tell you the rules of the test and ask if there are any questions. This silence can seem awkward in comparison to if you are in a music venue which could seem out of place and long. The silence from the music venue would seem even longer, but in the test setting where the silence was expected, the perception leads to the awkwardness that could contribute to how our brain perceives different types of silences and how we feel.
The third type of auditory illusion is called the “oddball silence” (Pressnitzer & McDermott, 2023). In this experiment, researchers attempted to measure how subjects interpret partial silence. To do this, subjects simultaneously listened to two different soundscapes. They compared a “target” silence (repetition of the same silence) to an “oddball” silence (a new, unexpected silence, like one of the soundscapes dropping out) (Pressnitzer & McDermott, 2023). Subjects perceived that the “oddball” silence was longer, even though it was not. The results from this experience mean that humans can perceive even partial silences as auditory events (Pressnitzer & McDermott, 2023).
This experiment shows human pattern recognition and adaptation. Once humans develop an understanding of a pattern, in this case auditory, any change from that pattern will trigger a change in brain perception. In this experiment the change from one sound cutting out to the other being silent results in a sense of longer silence perceived due to change of sound pattern. This reminds me of when a DJ does a break in their continuous set. Generally, this is only one second or two seconds of silence between songs. However, we can perceive this break as longer because we have been listening to the patterns and sounds throughout their set with no interruptions as a flow we have become accustomed to. During these breaks, we are accustomed to the sound constantly being there, and then the dancing stops because people don’t know how to act during this type of pause. Their bodies physically stop moving when the pause in sound occurs.
