<^Human Hearing> When a sound wave reaches our ears, how does our brain know it’s there, and know what that sound sounds like?
If you could follow a sound wave as it reaches your head, what would you see? First, funny flaps of skin and cartilage on either side of your head called “ears” catch the vibrations of the air and funnel them into a small, narrow passage called the ear canal. At its inner end, the canal is blocked by a delicate sheet of tissue - the eardrum. The vibrations of the sound wave push back and forth on the eardrum, making it also vibrate back and forth.
On the other side of the eardrum sit three of the tiniest, most amazing bones in your body. Resting on the eardrum, the hammer is connected to the anvil, and the anvil is connected to the stirrup. Each bone is vibrated in turn by the vibrations of the eardrum. The stirrup rests against the end of a snail-shaped, liquid-filled organ called the cochlea. The vibrations pass into the liquid inside the cochlea, and wiggle just a particular few of millions of tiny hair-like cells attached to nerve endings. Which ones wiggle, and which nerves send signals to the brain, tells your brain what the <#5680,7><!frequency> and <#5681,8><!amplitude> of the sound is!
Look out at a busy street. Your eyes give you a single picture of what you see. But listen! You can hear a dog barking, a car horn honking, two people talking with each other, and a bird singing. . . all at the same time. And, you can tell them all apart! Because many different parts of the cochlea can respond to different sounds, your brain can keep track of each pitch, each loudness, and each pattern of all the different sounds.
