So What’s Really Going On Here?

You all know the basics about hearing. You know, for instance, about the holes on each side of our heads, with the funny-looking flaps and the microphones at the inner end of those holes. The holes are called ears, the flaps are called pinnas and the microphones are called eardrums. We also know that, somehow, the air pressure change detected by those microphones gets sent to our brain, and that what came into our TWO ears gets combined so that we can figure out where the sound is coming from. Probably, you also know some other stuff, such as that the limits of our hearing run from 20 Hertz to 20,000 Hertz, that bats and dogs hear much higher, that cats hear softer, yada yada.

If you’ve done your reading a little more carefully, you may know that the softest sound we can hear is called 0 dB Sound Pressure Level and that 120 dB SPL is the loudest sound we can stand, sort of. You may have heard stuff like 1% distortion is inaudible, but also heard that there are guys ‘n gals out there that can hear .001% distortion. You may even know the implication of those numbers.

But what isn’t really discussed, or perhaps even considered, is how and why our auditory systems works the way it does AS A SYSTEM. We gloss over the difficult bit about how the sound gets from our eardrums to our brain (“Like, it just goes there, man. You know, like, through the nerves. Yeah, that’s right, it goes through the nerves, which are just like Monster Cable!”). Nor do we really consider how, or why, it evolved as it did, other than a tired line or two about needing to be able, as cave-persons, to localize the saber-toothed tiger just before being converted into deviled ham.

The Auditory System

So let’s look at the big picture (er, sound), for a second. We’ve got the mechanical sensing system, called the ears. Then there is a transducing system in the inner portion of each ear that converts the detected mechanical motion into neurological impulses. These impulses get sent to a portion of the brain called the auditory cortex via bundles of auditory nerves (which deserve some serious consideration all by themselves) and a series of intermediate stages in the nervous system and brain. During this transmission process a lot happens to transform the neural information that was sent from the ears. Auditory neural impulses from the two ears get integrated together (exactly how, we don’t know). These auditory neural impulses are also sent to the central nervous system as information to act upon and react to. Sensations of pitch, loudness and direction are extracted and/or derived from this auditory neural information. Finally, the evolved and transformed neural information is sent to the frontal lobes of the brain for perceptual activities like speech processing, identification, memorizing, and conscious perception – all the easy fun stuff that we know and love so well and so much. It is an extraordinarily complex system, and it does not yield to simplistic explanations about how we so easily and seamlessly perceive our beloved soprano digeridoo.

As Observed By Zork-11 From Betelgeuse IV

So let’s look at it from another direction. What is this system trying to accomplish? Let’s consider it from the perspective of a visiting alien trying to figure this out. First off, the physics of it are this: the auditory system is detecting the short-term pressure emissions given off by other organisms and the environment in general as a by-product of their regular activities, over a fairly broad range of frequencies and almost the entire linear range of pressures possible in the gas medium (air) in which we live. The system permits us to detect, localize, identify and (sometimes) communicate with a few of these other organisms (we call them Humans and Golden Retrievers) in a three-dimensional space around us. In addition, the system permits us to detect, localize and identify the environment as well.

Think of it. We live in this transparent gas called air, and we are really good at detecting short-term patterns of very slight pressure changes in this gas over a huge set of ranges. And not only do we use this pressure-variation detection ability to determine what is going on around us, we also make up and generate little pressure-variation patterns in this gas just for the fun of it (which we call music)! And we exchange precious metals between us in return for the fun of detecting such “cute” patterns of gas pressure-variation! Whoa!

Zork-11 is impressed!