Some people can hear Taylor Swift’s latest song, yet have no ability to know if she – or anyone else - is actually singing on it. They can process her backing instruments just fine. Just not her vocals. This deficit is not unique to the popstar. It’s true for any music they encounter.
After all these years, researchers have no clear explanation for this weird fact.
Or these facts: There are people who lose the ability to hear dogs barking after suffering strokes, yet easily retain the ability to hear every other sound. There are patients who hear dogs just fine, yet lose the ability to hear babies cry. Some stroke patients can hear people talking clearly, but lose the talent if those same people start singing. What light, if any, do these good folks shed on how we hear things normally?
As discussed last entry, the truth lies somewhere in the processing centers of the auditory cortices, those twin neural recording studios above your left and right ears. We now know these regions are wired with circuitry tuned to processing the type of sound you encounter. We call these circuits “what” information pathways. From dogs to opera singers, the cells in these circuits process incredibly specific aural inputs. When those cells are damaged, you can no longer process them.
Other circuits within your auditory studios are dedicated to processing the location from which the sound is derived. These are called “where” information circuits. The localization arises, in part, from the biological fact that your ears are on opposite sides of your head. This arrangement allows sound to enter those ears at slightly different times (unless you’re sitting directly in front of a sound source). Your brain is talented enough to calculate the arrival differences, using the dissimilarities to determine the location of the source.
Researchers have spent years characterizing the biological substrates behind these phenomena. Progress has been slow, and, in some cases, surprisingly unexpected. There are patients, for example, who suffer from “pure verbal agnosia” (not being able to understand speech), yet the only observable brain damage lies in their brain stems. These regions are famously known for controlling breathing, blood pressure and sleep.
But not speech.
We also know these areas are equipped circuits with built-in filtering systems, some of which are devoted to privileging specific auditory experiences. Music is one famous example. When you hear something, one filtering question turns out to be: “Is what I’m hearing musical in nature, or something else?”
If that answer is “musical”, your brain grants itself permission to activate a web of circuits researcher Isabelle Peretz calls the music module. Because music is such specialized sound – and since every culture on earth has some form of musical expression - we are going to switch gears in the upcoming entries and talk about the subject.
There must be some explanation as to why some stroke patients can hear the instruments behind the songs of their favorite popstars, yet have no ability to know if they are actually singing in them.
TWO QUICK HOUSEKEEPING NOTES …
… both concerning the holidays.
First: after more than 40 weeks with an unbroken stream of entries, I am taking the next two weeks off. When I return, we will dive head-first (literally!) into our near-musical journey.
Second: you might recall few weeks back I asked for comments regarding new topics to add to this space. These are topics for which you might be willing to pay using Substack’s subscription guidelines. I have had a chance to peruse your comments – wonderful, thoughtful stuff - and I will share some fun updates in the new year. Please rest assured, the free entries will remain regardless of any new subscribable material I might add in the future.
As ever, I am delighted to share these insights into the brain and look forward to our continued interactions at the start of a new year. Happy Holidays, everyone!
REFERENCES
Micelli, G., and A. Caccia. "The Auditory Agnosias: A Short Review of Neurofunctional Evidence." Curr Neurol Neurosci Rep 23, no. 11 (2023): 671-79.
van der Heijden, K. et al "Cortical Mechanisms of Spatial Hearing." Nat Rev Neurosci 20 (2019): 609-23.
Peretz, I. "Music, Language and Modularity Framed in Action." Psych Belgica 49, no. 2,23 (2009): 157-75.