What is meant by “absolute thresholds?”

            We exist in a sea of energy. At this moment, you and I are being struck by x-ray and radio waves, ultraviolet and infrared light, very high and very low frequency sound waves. But to all of them, we are blind and deaf. The shades on our sense, our windows on the world, are open just a crack, allowing us only a restricted awareness of this vast sea.

            To some kinds of stimuli we are exquisitely sensitive. Standing at the top of a mountain on an utterly dark, clear night, we can, given normal sense, see a candle flame atop another mountain 30 miles away. In a silent room, we can hear a watch kicking 20 feet away. We can feel the wing of a bee falling on our cheek and smell a single drop of perfume in a three-room apartment.

            Our awareness of these faint stimuli illustrates our absolute threshold—the minimum stimulation necessary to detect a particular stimulus (light, sound, pressure, taste, odor). To measure absolute threshold, we record the stimulation needed for detection 50 percent of the time. For example, to test your absolute threshold for sounds, a hearing specialist exposes each ear to varying sound levels. For each pitch, the hearing test defines where half the time you correctly detect the sound and half the time you do not. For each of the sense, that 50-50 point defines your absolute threshold.