Because of light, we see things around us—and even things, such as stars, that are far from us. Because of sound, we hear things. Sound travels as waves through air and water and even through solid substances. When those waves reach our ears, our eardrums and the tiny bones behind them move, and nerves carry messages about those movements to our brains. Loud sounds and soft sounds, high sounds and low sounds, brief sounds and continuing sounds—all these are faithfully reported to our brains. Sometimes we enjoy the sounds we hear. Sometimes they warn us of dangers to which we must react. Sometimes we ignore what we hear. Even while we sleep, even while in a coma, we continue to hear, because our ears (unlike our eyes) have no muscles. Therefore, we should never assume that a person in the room with us cannot hear the things we say.
Our hearing is not identical, even as our seeing is not identical. Some people hear higher pitches than other people; some people hear lower sounds than other people. My sister and her household once had a singing refrigerator—all day and all night, it alternated through three high-pitched tones, not shrill and piercing tones, but sounds that were present to those who could hear them. Her husband and their daughter could not hear the refrigerator sing. They thought my sister was inventing a story when she mentioned its song. When my children and I commented on the song, my brother-in-law and niece thought we were joining my sister in her joke. They could not hear those three sounds. As a result, they assumed that no such sounds existed.
We smell various scents when small particles of matter in the air reach our noses. Flowery perfumes, smoke, food cooking on the stove, freshly-cut grass, the plastic in a new car—all have distinctive odors that we notice when those particles enter our noses. Taste works like smell, except that we taste only the things that we put into our mouths. Sugar is sweet, acidic foods are sour, alkali foods are bitter, and salt is, well, salty. Chocolate is both sweet and bitter; lemonade is both sweet and sour. Whenever we taste something, our tongues report to our brains what we are eating, and our brains decide how much we like what we are eating. Most flavors combine both scent from the nose and sensations from the tongue, which is why food tastes different when our noses are obstructed due to colds or allergies.
The skin on our bodies includes nerve endings that tell us about the things we touch. These distinguish hot and cold, sharp and dull, soft and firm, and various other distinctions. They also report the intensity of contact, presenting pain when the touch is dangerous. The nerve endings in our skin are constantly reporting to our brains everything that touches them. The brain then decides how to react to the information it is receiving from our skin.
Our brains, then, are constantly responding to a variety of messages about sight, sound, scent, taste, and touch. Our brains are constantly judging which information to ignore and which information requires a response. If we are focused on one situation—if, for example, we are reading—the brain will ignore many of the other messages about sound and scent and touch that it receives. On the other hand, if we are reading and then smell smoke and hear the wail of the smoke detector, the brain decides to ignore the written message and to react to the other messages. While driving a car, we pay attention to many things: the road conditions, the behavior of other vehicles, and the signs and signals along the road, for example. We might listen to the radio, but the sound of a siren diverts our attention. If we smell gasoline, we wonder whether the source of that odor is from our vehicle, from the old pick-up truck next to us on the road, or from the gas station we just passed. If the ride is bumpy, we wonder if the pavement is rough or if a tire is going flat. We will notice other things—that car that just passed us has a license plate from Wisconsin; the price of gasoline went up four cents since yesterday. Our brains note some of the things reported to them, respond immediately to some, note others for later reflection, and ignore and forget many of the things our senses report. At any moment, our brains are discounting much sensory information as irrelevant—the touch of clothing on our arms, the ticking of the clock, the color of the floor and the walls, the lingering scents from our last meal. Our world is too busy; we could not survive if we continually noticed every sight and sound and scent and touch and tried to respond to all that information. And all this does not begin to address other information available to us, including memories and abstract concepts. J.