Sunday, June 17, 2007

This Is Your Brain on Music: The Science of a Human Obsession (Daniel J. Levitin)

Music is one of those things—like walking, having a conversation, or catching a fly ball—that it’s easy to take for granted until you start wondering how, exactly, we do that. (Or, in the case of catching a fly ball, how other people do that.) After all, listening to music is really just sensing changes in air pressure. Why, and how, do we turn those into rhythm, melody, song? Why do different instruments sound different? What happens when our brains follow a beat? How much of music perception is hard-wired, and how much is learned? Why do we like the music we do? Why do some songs get stuck in our heads, even when we don’t like them?

Levitin, a session musician and recording engineer before pursuing a Ph.D. in cognitive neuroscience, spends a lot of his time thinking about these kinds of questions, and This Is Your Brain on Music is an attempt to answer some of them. The bad news is that a lot of the time, the answer eventually adds up to “We don’t really know yet, not really.” The good news is that what they do know is fascinating, and gives at least a tantalizing glimpse into the still largely mysterious world of the brain.

For example: When we hear a harmonic tone—a plucked guitar string, a note from a flute—we’re not actually hearing a single vibration, but many different vibrations, typically in integer multiples of the fundamental tone (e.g., a 100 Hz fundamental has overtone vibrations at 200 Hz, 300 Hz, etc.; a 210 Hz fundamental has overtone vibrations at 420 Hz, 630 Hz, etc.). Our brains resolve that into the basic fundamental note—what we actually hear is a 100 Hz note or a 210 Hz note. In fact, our brains our so good at this that if you artificially create only the overtone frequencies, we will still hear the correct fundamental note.

OK, so that’s pretty interesting. How about this:

Petr [a graduate student] placed electrodes in the inferior colliculus of the barn owl, part of its auditory system. Then, he played the owls a version of Strauss’s “The Blue Danube Waltz” made up of tones from which the fundamental frequency had been removed. Petr hypothesized that if the missing fundamental is restored at early levels of auditory processing, neurons in the owl’s inferior colliculus should fire at the rate of the missing fundamental. This was exactly what he found. And because the electrodes put out a small electrical signal with each firing—and because the firing rate is the same as a frequency of firing—Petr sent the output of these electrodes to a small amplifier, and played back the sound of the owl’s neurons through a loudspeaker. What he heard was astonishing: the melody of “The Blue Danube Waltz” sang clearly from the loudspeakers. . . . We were hearing the firing rates of the neurons and they were identical to the frequency of the missing fundamental. The overtone series had an instantiation not just in the early levels of auditory processing, but in a completely different species.

I bet that was a pretty mind-blowing moment.

The book ranges over a wide variety of subjects, from what happens in our brains, exactly, when we listen to music; how we categorize it, and how that relates to our capacity for categorization in general; how we acquire our taste in music; how and why music affects us emotionally; what makes expert musicians different from the rest of us; and possible evolutionary sources for our musical sense. (Ask the owls what they’re doing restoring missing fundamentals!) It’s a fascinating read from an author who’s obviously passionate (and thoroughly knowledgeable) about both music and the mysteries of neuroscience.

1 comment:

daphne said...

Wow that is amazing. I’m a graduate student in speech-language pathology and I have classes on all of these themes: neuroscience, audiology, speech science, and anatomy physiology. Sounds like this guy wrapped up all my classes into one book. Isn’t it fascinating? We know so much about the brain, but really we know nothing.

Also, for anyone who is interested in this theme, NPR has a program called Radio Lab. One of my favorite episodes called “Musical Language” deals exactly with this issue. I have the link below if anyone is interested.

Happy Listening!