Unexplainable

The Sound Barrier #1: The myth of hearing

November 3, 2025

Key Takeaways Copied to clipboard!

  • Much of what we perceive as sound is not a direct reading of external pressure waves but is actively constructed, filtered, and edited by the brain through top-down processing based on expectation and experience. 
  • Auditory illusions, such as those discovered by Diana Deutsch, demonstrate that the brain prioritizes making sense of the world (e.g., suppressing echoes, separating pitches) over accurately relaying raw sensory input. 
  • The brain's remarkable ability to remap and reconstruct auditory input, evident in cochlear implant users retraining themselves to understand speech and music, highlights the powerful, often unexplainable, influence of expectation on perception. 

Segments

Introduction and Sponsor Reads
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(00:00:00)
  • Key Takeaway: The episode is sponsored by Anthropic (Claude) and Schwab, setting the stage for exploring complex questions.
  • Summary: The segment begins with sponsor messages from Anthropic (Claude) and Schwab, followed by the host, Noam Hasenfeld, introducing the podcast Unexplainable and the theme of the series, ‘The Sound Barrier,’ focusing on the myth of hearing.
Diana Deutsch’s Defining Moment
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(00:01:06)
  • Key Takeaway: A childhood mishap during a BBC performance clarified for Diana Deutsch that she was not meant to be a performing musician.
  • Summary: The host introduces Diana Deutsch, whose career path became clear after an embarrassing incident at age 16 while page-turning for her music teacher at the BBC, realizing performing wasn’t for her.
Discovery of Auditory Illusion
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(00:02:48)
  • Key Takeaway: Diana Deutsch discovered a profound auditory illusion in 1973 where the brain separates simultaneous tones into distinct spatial locations.
  • Summary: Deutsch shifted to researching music psychology, leading to her 1973 experiment where playing alternating high/low tones in each ear resulted in hearing a single high tone in one ear and a single low tone in the other, regardless of headphone swapping.
The Brain’s Auditory Editor
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(00:05:10)
  • Key Takeaway: Much of what we hear is constructed or edited by the brain, not just a direct perception of external sound waves.
  • Summary: The host reflects on Deutsch’s discovery, framing the four-part series, ‘The Sound Barrier,’ around how the brain constructs our auditory experience, starting with the basic physics of sound waves.
Physics of Sound vs. Perception
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(00:06:19)
  • Key Takeaway: Sound is physical pressure waves converted to electrical impulses in the cochlea, but the brain actively suppresses echoes to make sense of spatial location.
  • Summary: Audiologist Matthew Wynne explains the known process of sound transmission (pressure waves, eardrum vibration, cochlea conversion). The host then notes that the brain edits out echoes via ’top-down processing’ to prevent confusion.
The Scale Illusion Explained
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(00:09:34)
  • Key Takeaway: Deutsch designed the ‘scale illusion’ to show the brain reorganizes sounds based on expectations, such as grouping high and low pitches separately.
  • Summary: Deutsch’s subsequent work led to the ‘scale illusion,’ where alternating high/low notes in both ears are perceived as all high notes on one side and all low notes on the other, demonstrating top-down processing based on pitch expectation.
Top-Down Processing and Expectation
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(00:13:16)
  • Key Takeaway: Perception is often a prediction of what the sound should be, illustrated by the ‘mysterious melody’ illusion.
  • Summary: The concept of top-down processing is defined. The ‘mysterious melody’ (Yankee Doodle scrambled across octaves) is played; listeners only recognize it once they have context (expectation) from hearing it in a single range.
Geographic Influence on Pitch Perception
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(00:16:27)
  • Key Takeaway: Life experience, specifically the pitch range of childhood speech, can influence whether an ambiguous musical interval is perceived as rising or falling.
  • Summary: Deutsch’s experiment showed that people from Southern England tended to hear an ambiguous tritone pattern as rising, while Californians heard it as falling, linking pitch perception to regional speech exposure.
Mike Korused’s Hearing Loss Journey
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(00:19:04)
  • Key Takeaway: Mike Korused, who lost his hearing later in life, relied on music, especially Bolero, as an auditory touchstone before sudden deafness.
  • Summary: The episode transitions to Mike Korused, who used hearing aids and was obsessed with Ravel’s Bolero. In 2001, he rapidly lost his remaining hearing, describing it as ‘pouring out of my head like water out of a cracked jar.’
Cochlear Implant Activation
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(00:24:56)
  • Key Takeaway: Upon activation, Mike’s cochlear implant produced high-pitched, distorted sounds, but his brain quickly adapted by remapping the input to match his preconceptions of pitch.
  • Summary: Mike received a cochlear implant. The initial sound was shocking—his own voice sounded like a ‘dementon mouse’ due to the implant’s tendency to interpret signals as high-pitched. His brain rapidly engaged in top-down processing to correct this.
Relearning Music with Implants
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(00:30:24)
  • Key Takeaway: Cochlear implants are optimized for speech, not music, due to limited electrodes causing ‘pixelated’ sound, making familiar music easier to enjoy through memory.
  • Summary: Music remains difficult for implant users because the technology simplifies frequencies. Mike found that familiar music like Bolero sounded better because his brain could use memory to fill in the missing quality, even if the input was incomplete.
Conclusion: Subjectivity of Reality
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(00:37:26)
  • Key Takeaway: Hearing is a subjective, constructed reality, meaning there is no single ‘real’ version of music or sound; it is shaped by individual experience.
  • Summary: The host and Deutsch conclude that our brains constantly build our auditory reality. This subjectivity applies to music interpretation, reminding listeners to be humble about their perceptions.
Next Episode Preview and Credits
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(00:39:47)
  • Key Takeaway: The next episode of ‘The Sound Barrier’ will focus on retraining the brain, inspired by the cochlear implant experience.
  • Summary: The host previews the next episode focusing on a listener with Tinnitus seeking advice on retraining her brain. Credits for production and support for Unexplainable are then read.