As all schoolchildren know, we hear with our ears. And as all schoolchildren also probably know, we hear with our brains — or if they don't know it, at least they must suspect it, given the way sounds around us seem to turn without effort into thoughts in our heads. But how? It's the interface between ear and brain where things get more complicated, but "Odyssey of the Ear," the six-minute video above, makes it much clearer just how sound gets through our ears and into our brains. Suitable for viewers of nearly any age, it combines silhouette animation (of the kind pioneered by Lotte Reiniger) with live action, projection, and even dance.
According to the video, which was originally produced as part of HarvardX's Fundamentals of Neuroscience course, the process works something like this. Our outer ear collects sounds from our environment when things vibrate in the physical world, producing variations in air pressure, or "sound waves" that pass through the air.
The sound waves enter the ear and pass down through the auditory canal, at the end of which they hit the ear drum. The ear drum transfers the vibrations of the sound waves to a "series of little bones," three of them, called the ossicles, or "hammer, anvil, and stirrup." These transmit the sounds to the fluid-filled inner ear through a membrane called the "oval window."
Inside the inner ear is the snail-shaped organ known as the cochlea, and inside the cochlea is the organ of corti, and inside the organ of corti are "thousands of auditory hair cells," actually receptor neurons called stereocilia, that "convert the motion energy of sound waves into electrical signals that are communicated to the auditory nerve." From there, "the signal goes into structures deeper in the brain, until at last it reaches the auditory cortex, where we consciously experience sound." That conscious experience of sound may make it feel as if we immediately recognize and consider all the noises, voices, or music we hear, but as "Odyssey of the Ear" reveals, sound waves have to make quite an epic journey before they reach our brains at all. At that point the waves themselves may have dissipated, but they live on in our consciousness. In other words, "the brain has taken what was outside and made it inside."
Based in Seoul, Colin Marshall writes and broadcasts on cities, language, and culture. His projects include the book The Stateless City: a Walk through 21st-Century Los Angeles and the video series The City in Cinema. Follow him on Twitter at @colinmarshall or on Facebook.