The Psychophysical Problem

Loudness

A sound has a variety of physical characteristics. For example, a pure tone can be described by its physical intensity (energy transported), its frequency (in cycles per second), its duration, and so on. The same sound has various psychological characteristics. For example, how loud does it seem? What emotional meaning does it portray? What images does it suggest? Since the middle of the nineteenth century, scientists have tried to study the relationships between the physical characteristics of stimuli like sounds and their psychological characteristics. Some psychological characteristics might have little relationship to physical ones. For example, emotional meaning probably has little relation to the physical intensity of a sound, but rather it may be related to past experiences, as, for example, with the sound of a siren. Other psychological characteristics seem to be related in fairly regular ways to physical characteristics. Such sensations as loudness are an example. Psychophysics is the discipline that studies various psychological sensations such as loudness, brightness, apparent length, and apparent duration, and their relations to physical stimuli. It attempts to scale or measure psychological sensations on the basis of corresponding physical stimuli. In this chapter, we shall describe some of the history of psychophysical scaling and its applications or potential applications to measurement of noise pollution, of attitudes, of utility, etc., and we shall discuss ways to put psychophysical scaling on a firm measurement-theoretic foundation. We shall concentrate on loudness.