Tech Talk: Your Brain on Music

05/02/2006 On April 21, our local National Public Radio outlet, WNYC, broadcast (and streamed over the Internet) an episode of the station's Radio Lab program. This slickly produced series combines aspects of NPR-style radio journalism with modern audio-studio production techniques that are the sonic equivalents of MTV-type visual effects. Much of the time I find that the high-tech machinations obscure the journalistic message. But the episode that aired on the 21st, and that is scheduled for a rebroadcast/restreaming at 2 and 3 PM EDT on May 16, should be heard by everybody interested in how the sounds hitting your eardrums are turned by your brain into music. You don't even have to wait if you don't want to, since MP3 streams of the program are available at www.radiolab.org. Look for the program titled "Musical Language."

The first segment of the three in the show quite rightly centers on Diana Deutsch, a psychology professor at the University of California in San Diego and one of the pioneering researchers in the fundamentals of music perception. Her website (http://psy.ucsd.edu/~ddeutsch/) is a great place to read, listen, and download, especially her famous work on musical illusions, one of which is illustrated here in musical notation: 0605_dd_chromatic

You can even order a couple of CDs of musical illusions, nearly all of which are ear-openers. I recommended both of them.

Radio Lab's coverage of Deutsch's work focuses on her "discovery" that when listening to multiple repetitions of a spoken phrase - Deutsch saying "But they sometimes behave so strangely" in a recorded lecture, for example - you can actually pick out an internal musical melody in ordinary speech. This effect had already been exploited decades ago by composers like Steve Reich, whose 1966 Come Out is available from Apple's iTunes store. The melody Deutsch heard in her phrase, and which receives the full weight of Radio Lab's production values, is shown here in musical notation: 0605_dd_sostrangely

This is a good example of the hearing system's propensity to extract a "central pitch" and to create a perception of a melody from the extracted pitches even when the input to the ear is not intended or produced as music. Deutsch believes this power is partially suppressed in most Western listeners but operates, as it must, at full force in speakers of "tonal" languages, such as Chinese, where the meaning of a syllable or word can be changed by the melodic contour with which it is spoken. (Ancient Greek operated in this way, too.)

But when I first heard this demo, available for download in full at Deutsch's website, my ears heard the first note not as a D-sharp, as Deutsch would have it and as shown in the notation, but more as a C-sharp, a whole tone lower. The spectrum analyzer contained in Adobe Audition (an excellent pro-grade PC sound editing program that contains its own pitch-estimation algorithm) confirmed my impression. In order to convince you of my interpretation, and as an example of how "pre-biasing" can force you to reinterpret the sounds you hear, I've prepared my own demo containing an excerpt of Deutsch's original track (in the right channel) with my own "guide-pitch" track of pure-spectrum sine waves in the left channel. The effect of the slight initial melodic C-sharp/D-sharp curve, rather than Deutsch's repeated D-sharps, is actually more audible when heard in reverse, a ploy that disturbs the pitch-extraction/melody-formation process.

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