Unexplainable: "The Sound Barrier #1: The Myth of Hearing"

Podcast: Unexplainable (Vox)
Date: November 3, 2025
Host: Noam Hassenfeld
Guests/Contributors: Diana Deutsch, Matthew Wynn, Mike Chorist

Episode Overview

The debut episode of "The Sound Barrier" miniseries delves into the mysterious and often counterintuitive mechanics of human hearing. Through case studies, personal anecdotes, and expert interviews, the episode explores how our perception of sound is not just a direct translation of vibrations in the air but a constructed experience, shaped by our brains, expectations, and life history. This episode features pioneering psychologist Diana Deutsch's discovery of auditory illusions and follows science writer Mike Chorist's journey after losing his hearing and relearning to experience music through a cochlear implant. The central theme: what we "hear" is as much a product of our mind as of our environment.

Key Discussion Points & Insights

1. Diana Deutsch and the Discovery of Auditory Illusions

• Diana's Early Experiences:
  Diana Deutsch recounts an early aspiration of being a musician, sharing a formative, humbling moment as a page-turner at the BBC that led her toward the science of music perception rather than performance.

  • "It certainly made me realize that being a performing musician was probably not a good idea for me." (02:38, Diana Deutsch)

• The 1973 Experiment:
  Diana describes experimenting with synthesized tones, leading to the discovery of an auditory illusion that demonstrates the subjective nature of hearing.

  • "...I started off with a high tone alternating with a low tone in one ear, and at the same time, a low tone alternating with a high tone in the other." (03:24)

  • Only high tones perceived in one ear and low in the other, despite both ears receiving both tones. Flipping headphones made no difference.

  • She quickly tested dozens of people—most heard the same illusion.

• Significance:
  The experiment demonstrated that perception of sound is constructed by the brain and not always a direct reflection of physical stimuli.

2. The Mechanics of Sound Perception (w/ Matthew Wynn, Audiologist)

• The Physical Process:
  Sound is described as vibrations—pressure waves—converted by ears into electrical signals for the brain.

  • "Sound is rapid changes in air pressure that happen when something is vibrating." (06:24, Matthew Wynn)

• Brain 'Editing':
  The brain ignores many physical details (like echoes) to present a coherent auditory scene.

  • "Thankfully, our brain knows sounds only come from one direction. And that's the only way the world makes sense." (08:40, Matthew Wynn)
  • "...our brain essentially edits our auditory experience." (09:09, Noam Hassenfeld)

3. Diana Deutsch’s Further Illusions Provoking ‘Top-Down’ Processing

• Scale Illusion:
  Another auditory illusion, where the brain groups high and low tones into separate streams, even as the actual sources alternate.

  • "One would assume that sounds...in a higher pitched range are coming from one source, and sounds in a lower pitched range are coming from another source." (11:40, Diana Deutsch)
    Not everyone perceives the illusion the same—left-handed vs. right-handed people show systematic differences.

• Top-Down Processing:
  The brain’s application of prior knowledge and expectations shapes what we hear.

  • "Top down processing occurs when the brain uses expectation, experience, and also various principles of perceptual organization to influence what is perceived." (12:43, Diana Deutsch)

• Auditory Expectations and Recognition:
  Demonstrated with the 'mysterious melody' illusion—familiar melodies scattered across octaves are unrecognizable until context is provided.

• Cultural and Learned Variation:
  For ambiguous sound patterns, perception varies by individual and even by where someone grew up.

  • "It has to do with the pitch range of the speech to which you have been most frequently exposed, particularly in childhood." (17:58, Diana Deutsch)

4. Case Study: Losing and Regaining Music via Cochlear Implant (Mike Chorist)

• Mike’s Story:
  Born with severe hearing loss, Mike grew up loving music—especially Ravel’s Bolero—as a benchmark of his hearing.

• Sudden Hearing Loss:
  In 2001, Mike lost his residual hearing abruptly, an experience he describes vividly.

  • "It was like my hearing was pouring out of my head like water out of a cracked jar." (24:40, Mike Chorist)

• Cochlear Implant Experience:
  After implant surgery, his first hearing experiences were jarring and unnatural.

  • "And my voice sounded really weirdly high pitched. I almost sound like...it was like listening to a demented mouse." (26:19, Mike Chorist)

  With time, his brain adjusted, 'remapping' the unfamiliar input into recognizable sounds through training and cognitive adaptation.

  • "My brain was saying, okay, this is my voice. I know it's supposed to be low pitch. ...I know it's a low pitch, I'm going to interpret it as a low pitch." (27:15)

• Training the Brain:
  Mike practiced extensively, reading along with audiobooks to rebuild the connection between sounds and meaning.

  • "So it is a process of remapping." (28:58, Mike Chorist)

  Audiologist Matthew Wynn contextualizes Mike’s journey as a typical 'miracle' of brain plasticity, mysterious even to experts.

• Music vs. Speech Perception:

  • Cochlear implants are optimized for speech, not music. Musical perception remains extremely challenging due to the limited frequency resolution and overlapping signals.
  • "The current design of cochlear implants isn't set up really for music. It's set up to understand speech." (31:34, Matthew Wynn)

• Simulations of Implants:
  Mike cautions about listening to simulations of cochlear implant sound—they only reflect the software's output, not the complex, changing perception of a real user.

5. The Brain’s Subjectivity in Hearing

• Familiarity Fills Gaps:
  Familiar music becomes enjoyable again because the brain fills in missing details.

  • "And I think it's a testament to the brain filling in those gaps, conjuring the memory of what the sound quality should be." (35:54, Matthew Wynn)

• Variety of Musical Experience:
  Everyone’s brain constructs a slightly different version of 'the music,' shaped by life history, expectations, and neural adaptation.

  • "When an orchestra performs a symphony what is the real music?...there's no one real version of the music, but many." (37:57–38:15, Diana Deutsch)

• The Central Mystery:
  Despite knowing the brain performs these feats, scientists still don't understand the exact mechanisms.

  • "We do this very complex calculation, but I don't think that we really know exactly how it's done." (37:18, Diana Deutsch)

Notable Quotes & Memorable Moments

• On Brain Editing:
  "The way I like to phrase it is that the brain is being nudged in a direction rather than just straight out reading the world." (09:15, Matthew Wynn)

• On Illusion Discovery:
  "I was beside myself. It seemed to me that, you know, I'd entered another universe or I'd gone crazy or something." (04:49, Diana Deutsch)

• On Auditory Subjectivity:
  "To some extent, our brain is hearing what we are expecting to hear." (13:11, Diana Deutsch)

• On Music Through an Implant:
  "I wanted my bolero back." (31:40, Mike Chorist)
  Even after training, some aspects of the musical experience remain elusive—“But there are things that I know that I'm missing." (36:10, Mike Chorist)

• On Diversity of Auditory Realities:
  "The answer is surely that there's no one real version of the music, but many. And each one is shaped by the knowledge and expectations that listeners bring to their experiences." (38:15, Diana Deutsch)

Timeline of Important Segments

| Timestamp | Segment/Topic | |-----------|------------------------------------------------------| | 01:03 | Diana Deutsch's origin story and moment of clarity | | 03:10 | Deutsch's experiment with synthesized tones | | 06:24 | Matthew Wynn explains sound perception basics | | 09:15 | Brain's role as auditory editor | | 10:21 | Discovery and explanation of scale illusion | | 12:43 | 'Top-down' processing definition | | 14:05 | 'Mysterious melody' and role of expectation | | 17:58 | Cultural differences in auditory perception | | 22:46 | Transition to Mike Chorist's story | | 24:06 | Mike's sudden hearing loss | | 26:11 | First experiences with a cochlear implant | | 27:55 | Relearning sounds through brain adaptation | | 29:04 | Audiologist on time course of cochlear adaptation | | 31:34 | Cochlear implants: speech vs. music | | 34:19 | Simulations: hardware/software vs. user experience | | 35:40 | Improvement via training and tweaks | | 36:07 | Brain fills in familiar gaps in music | | 37:57 | What is "real" music? Multiple realities of listening| | 38:27 | Reflection on subjectivity and humility in perception|

Conclusion

"The Sound Barrier #1" delivers a rich scientific and human narrative, illustrating the deeply subjective and adaptive nature of hearing. Through personal stories and expert guidance, the episode demonstrates how our auditory reality is constructed—molded by brain processes, expectations, life experiences, and, sometimes, by extraordinary adaptation after profound loss. It sets the stage for the next installments, promising deeper dives into the unexplained frontiers of perception.

Next Episode Tease:
A listener with tinnitus reaches out to ask how to retrain her brain, inspired by the adaptation stories in this episode.