The human ear is an amazing organ. It's easy to overlook, but auditory input is an incredibly useful tool for the human brain. If you close your eyes and listen, you can still absorb a surprising amount of information about your surroundings without any visual input. The human ear can detect where a noise came from and about how far it has traveled due to a few simple characteristics of sound.
The human body has two ears for a reason. Two ears on opposite sides of the head provide sufficient information to the brain to help it determine where a sound is located in relation to the body. Most sounds that a human detectors are picked up by both ears. Without the source is directly in front of the body or directly behind it, the sound will be louder in one ear than another. For example, if a bird chirps on the right side of a person, the right ear will pick up the chirp loud and clear, while the left ear will only detect a small sound. The brain compares the volumes of each sound and uses this to determine from which direction the sound comes and how far away the source is.
When sound is emitted from a source, it travels in all possible directions. Sound most readily travels through gases and liquids, and any solid objects in its path will dampen the vibrations. Dampening a vibration makes its volume lower and can muffle characteristics that make the sound easy to identify. To the brain, a muffled sound can mean that the source is behind something (a speaker system in another room).
Since sound travels in different directions, it is shorter to bounce off of flat surfaces. In fact, when your ears pick up a noise, it often picks up multiple copies of that noise, some smaller and more distorted than others. Part of what makes your ears so adept at locating yourself in a room is due to this effect. Imagine yourself shouting in your living room and shouting in an empty gym. The sound of your voice does not change, but what your ears detect is very different depending on the room you are in.
Because the body gets so much positional information from the ears, problems with the ear can cause health issues seemingly unrelated to sound. People who complain of problems with balance or feel disoriented often get a hearing test as part of a checkup. A hearing test helps determine whether either or both ears has sustained permanent damage. If one ear is more damaged than another, a hearing test may help explain feelings of disorientation. Damage to both ears can make sounds harder to detect and can make a person feel disconnected from the world around him or her.
The body picks up information with its ears regularly, so it's important to take care of them. Avoid exposure to loud noises; even very loud noises for short periods of time can cause damage. If you think that you may have sustained damage to your ears, a hearing test can help evaluate how badly they are damaged and what can be done about them. After all, you do not want to be left completely in the dark when you close your eyes.