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Those of us who work in behavioral economics love discovering brain farts—cognitive biases and unconscious illusions that highlight the limitations of human nature. We enjoy uncovering hidden sources of irrationality — mental shortcuts that send people down the wrong paths. Indeed, some have referred to our field as being obsessed with “stupid human tricks.”
But every once in a while, I am reminded of just how brilliantly stupid the human brain is—how wonderfully intelligent our failings are.
Once such reminder jumped out at me from the pages of Daniel Levitin’s best-selling book This is Your Brain on Music. I’ll tell you about the particular mental illusion Levitin describes in a moment, but first I need to give you a quick lesson on the physics of music.
As most of us knew by the end of fifth grade, sound is the perception of vibration. Vibrations of course are back and forth movements that differ from each other in the speed, or frequency, of this back and forthness. But what most of us don’t know is that these vibrations typically don’t occur in isolation. If I strum a guitar string which, at its lowest, vibrates 100 times per second (or 100Hz), that string will also emit sound waves at 200Hz, 300Hz, 400Hz, etc. A string that, at its base, vibrates at 200Hz will emit overtones with frequencies of 400, 600, 800 and 1,000Hz. If a string emits overtones of 500, 750, 1000 and 1250 Hz, you can rest assured that the base tone will vibrate at a frequency of 250 Hz. (I find it incredible that musical overtones pay such close attention to math, that nature works out this way.)
I mention these overtones because they are a crucial part of what makes music sound the way it does. 100Hz on its own, without any overtones, wouldn’t sound like a normal note.
What do you think happens when the brain hears a musical tone that is made up of frequencies at 200, 300, 400 and 500Hz? Such a tone would never occur naturally. The only natural way for these overtones to occur, each spaced from each other by 100Hz, would be to have been produced by a 100Hz tone. Sound engineers, however, can remove the base tone, thereby exposing people only to the overtones.
You probably think this combination of overtones is going to sound funky, yes? Or at least like it will cause listeners to feel as if something crucial is missing. As it turns out, however, people listening to such artificially engineered tones “hear” the note as if it includes the 100Hz tone. Our brains fill in the missing information.
We are all unconscious acoustical engineers!
Levitin provides another example of this perceptual completion, a study by Richard Warren. In his experiment, Warren plays a tape of himself saying the sentence “the bill was passed by both houses of the legislature.” Except Warren cuts one of the words out of the sentence and replaces it with white noise. People listening to the recording don’t hear “the bill was passed by both HISSSS of the legislature.” Instead, they “hear” the entire sentence. They never notice the missing word. Instead, they almost universally report that they heard the whole sentence while also hearing extra white noised in the middle somewhere. Their brains fill in the missing information.
In my research and writing, I continue to worry about all the tricks our brains play on us. As a medical decision making expert, I worry that unconscious biases push doctors to recommend unwarranted treatments. I fear that hidden psychological forces influence patients to engage in unhealthy behaviors. And I plan to continue to uncover these hidden forces and design methods to help people overcome them.
But it’s good to remember once in a while that our brains do an amazing job of helping us humans make sense of an imperfect world.
