On The Neuroscience Of Magic And The Magic Of Aural Illusions In Music

by Thomas Brett

In their engaging book Sleights Of Mind, Stephen Macknik and Susana Martinez-Conde explore the neurobiology of attention in the context of the magician’s art.  They argue that illusions, slights of hand and other tricks have much to offer the study of how we think because magicians specialize in playing with our perceptions and (mis)guiding our attention.  Magic manipulates the reality of our here and now (242) and even “the nature of our conscious experience” (255).  For instance, our visual systems have a spotlight of attention beyond which we are almost blind.  Magicians capitalize on this by directing what we see in controlled ways, creating “frames” or windows of space to localize where and what we attend to (66).  Magic works its wonders over and over again by hacking into and manipulating our awareness and understanding of how we think the world should work.  Simply put, a magic trick succeeds when it manages to violate our expectations (159).

Magicians are not the first artistic community to have made important discoveries about our cognitive processes.  European painters in the 15th-century discovered the rules of perspective so that–presto!–paintings quickly moved from looking flat and oddly proportioned like this

to having a depth of field like this

and much more recently, toying with our sense of perception through impossible figures like this

What kinds of discoveries have music composers and performers made over the centuries?  After all, music, like magic, is also an art of holding the listener’s attention and awareness through time.  (Music may well be, as a friend once said to me, one of the provinces of magic.)  So what about aural illusions in music?  How does music create phantom presences out of such seemingly simple sonic materials?  Is it fair to say that music is an elaborate art of aural illusionry?

There are certainly many musics around the world that make use of different kinds of aural illusions to achieve their affect.  A few examples come to mind.  Consider, for instance, akadinda music from Uganda.  The akadinda is a large wooden xylophone played by several musicians at once.  The music consists of very fast interlocking patterns that whiz by at upwards of 300 beats per minute.  But what’s even more remarkable about this music is that its rapid-fire textures give rise to an auditory illusion called “inherent patterns.” First described by ethnomusicologist Gerhard Kubik about fifty years ago (Kubik has spent much of his life in the field studying and documenting music making in Sub-Saharan Africa), inherent patterns are resultant or composite melodic or rhythmic patterns that seem to (magically) rise to the surface of what is otherwise just a very dense musical texture.  Inherent patterns can be considered perceptual artifacts–patterns that arrive at our senses because they seem inherent or embedded in what we’re hearing.  In the case of akadinda music, if you listen through the fast interlocking rhythms you can sometimes hear a simple two note melody that no single musician is playing on their own.  Rather, the melody is the sum of several sets of hands playing adjacent akadinda keys.  Your brain notices this inherent melody because the fast interlocking pattern repeats insistently to the point that your brain can focus in and detect it.

Inherent melodies can be heard in other African musical traditions as well, such as mbira music from Zimbabwe.  In mbira music, you’ll sometimes hear performers sing along with the inherent patterns as they perceive them in the music they’re playing.  And the American composer Steve Reich has written numerous pieces (such as Drumming) that exploit this perceptual phenomenon as well.

Another musical example that taps our propensity for noticing sounds beyond sounds is throat singing from Tuva and Mongolia.  Skilled throat singers from these regions have evolved techniques that involve constricting their throats and shaping their lips in such a way that they can produce not one but two pitches at once.  The low-pitched droning note is called a fundamental and the higher pitched note an overtone or harmonic. With one (long) breath, a singer produces two distinct frequencies.  To our ears it sounds like two people are voicing sound, the higher pitched voice making an ethereal whistle.

A final example of musical illusions can be heard in the fugues of the German Baroque composer J.S. Bach (1685-1750).  A fugue is a type of intricate composition for several musical voices (or musical lines) in which each voice has its own independent melody that coexists and interacts with those of the other voices.  In a fugue, a theme is introduced by one voice, then picked up by the other voices as they enter, one by one, in different pitch registers.  Once all the voices are in and chattering away, the fugal texture can sound a little chaotic but it all holds together through careful musical design.

If you listen to Bach’s (unfinished) Art Of Fugue (composed circa 1740s), you can hear the four distinct voices enter one at a time and make a multi-part musical conversation.  What is interesting in terms of aural illusions, however, is how your ear, upon hearing a voice entering the texture (for instance, voice two enters at 0:12), tracks that voice for a while as it articulates the fugue’s theme.  This narrowing of your attention on one fugal voice–would Macknik and Martinez-Conde call it auditory “framing”?–continues until you are distracted by a new voice making its entrance (at 0:20) and then yet another one (at 0:30).  The magic of a great fugue composer like Bach is to design a musical texture that can guide your attention in a way that is satisfyingly challenging.

As with the magician’s art, engaging music presents us–with or without our consent–with a set of perceptual problems to figure out, whether they be inherent patterns, phantom overtone melodies, or fugal counterpoint equations.

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