Natural noise is often described somehow differently from anthropogenic noise, but why? Is it because animals evolved and machines were built? In different environments wind and rain are noise, whereas in others music would be considered noise. In urban environments we might hear the drone of a fan, the rumble of a nearby highway, the constant chatter of your office, or the hum of some machinery somewhere nearby. This is noise pollution, and it affects how our brains focus.
We don’t really know exactly why we evolved to make noise, it just happens. At some point, likely when amphibians moved out of water, hearing became an advantage. Those which could sense vibrations better lived, and those that couldn’t got crushed by the tree falling in the woods (that definitely made sound). Recent Harvard research stated that “lungfish… lack a middle ear to sense pressure changes, [but] they are able to detect sounds in the air through vibrations.” Caterpillars, on the other hand, hear through the hair on their bodies.
Once we were able to hear, we had to evolve a way to avoid excessive noise. Mammalian brains are incredibly good at picking auditory signals out of the noise. “Novelty detector neurons” are located in the dorsal and external cortex of the inferior colliculus. First we hear a sound, then the neurons fire. With repetition, they “get bored” and learn to ignore sounds. But, if a parameter of the sound is changed the neurons get excited again. This is how we know what sounds to listen to.
Special thanks to Mike Rugnetta for helping with this episode! Check out his podcast, Reasonably Sound, on Apple Podcasts or at ReasonablySound.com.