The Psychophysical Law
One of the fundamental issues in psychophysics concerns the form of the psychophysical law. The problem is that of discovering a simple equation which describes how the intensity of stimuli and our impressions of them are related. The solution of the problem would have far-reaching implications for scholars in a variety of fields. Certainly, the philosopher's concepts of epistemology and the psychologist's theories and research on information processing would be influenced by a psychophysical law. No doubt the neurophysiologist's search for the mechanisms by which the nervous system encodes environmental stimuli would be facilitated. Perhaps even some of the difficult problems confronting social scientists in their attempts to understand human behavior in social environments would become somewhat simplified by a psychophysical law. The law would probably have a variety of practical applications even in fields such as architectural design, communication systems design, the arts, medicine, and law.
One of the first efforts to formulate a psychophysical law was that of Daniel Bernoulli ( 1738). Bernoulli, a mathematician, was interested in the psychological worth of money. He proposed that people do not act on the basis of the actual value of money but on some psychological transformation of the actual value. It seemed to Bernoulli that the utility of money increases at a decreasing rate as the actual amount increases. A gain of one dollar is psychologically greater if you have only two dollars than if you have one hundred dollars. The economist would say that money exhibits a decreasing marginal utility. Bernoulli's specific proposal was that the utility of money increases as a function of the logarithm of the amount of money. Over 100 years later, Fechner proposed a logarithmic function for sensations and stimuli.