Seeing, tasting, touching things, all deal with a chemical reaction at some point in their process. Hearing, on the other hand, deals completely with mechanical interactions between one's ears and the world making noise around them.
As objects vibrate in their environment, they produce sounds. Those vibrations push and pull air back and forth to create different frequencies, compression, amplitudes, etc. All these factors relate to how high pitched, loud and continued a sound might be. In order to hear these various aspects of sound, one must have ears in good working order.
Mothers have been proponents of healthy hearing processes for thousands of years. Somehow, they knew that by keeping one's ears cleaned and free of debris, the person would be able to hear better, let alone have a better public appearance.
The explanation for this deals with the fact that as those vibrations are traveling through the air, the outer ear collects the sounds, or impulses at this point, and directs them into the ear canal. From here the vibrating air travels further in towards the ear drum.
If this canal is blocked by debris, notably ear wax, or excessive hair, the vibrations are dampened, much like what happens when a horn blower covers their instrument's opening (only in reverse; the horn's sound is looking to get out of the instrument.) So, good healthy hearing starts with keeping one's ears clean and free of debris.
Evolution has slowly removed a human's ability to move their ears independently from the rest of their head; unlike other mammals, notably dogs, cats, and other wild things, most of which still have the ability to swivel their ears towards a sound's direction. These are survival aspects of those species which man has grown away from needing.
Still, our biology provides us with the ability to discern where a noise originated from. Our stereo hearing capability tells us the general direction from us where the noise was created, and the outer ear also helps us determine whether the noise is in front of or behind us.
Once the noise vibrations have been captured by one's outer ear and sent traveling inwards, they eventually come to the ear drum. This taut piece of specialized skin acts to capture the motion of the sound's vibrations and essentially reverses the process of the original object which created the sound to begin with.
Compressions and rarefactions push and pull the ear drum causing electrical impulses to be generated and sent to the brain via the auditory nerves. Before this happens however, there are a few more steps to the hearing process.
Attached to the inside of one's ear drum is the first of three tiny bones--the smallest in the human body. These bones act to move the sound vibrations from the ear drum to the inner ear as well as increasing the amplification of the sound. This is necessary in order to convert the sounds to electrical impulses.
The sound energy is converted to electrical in the fluid part of the inner ear. A series of complex reactions occur which provide the auditory nerve with a signal that transmits the sounds to the brain for deciphering and processing.
Different parts of the inner ear affect the signal strength of the impulses sent to the brain for processing. Louder noises send stronger signals, higher pitched sound send very specific signals to one's brain.
While relatively simple in function, the process of hearing is still quite amazing and complicated to understand.