Decision Theory and the Concept of Threshold in Psychophysics

Psychophysics deals basically with how signals are perceived. It is assumed that a signal or stimulus is perceived after it reaches a certain threshold value, called the sensory threshold. Thus, there are two possible states: either a signal is perceived by the neuronal system, or it is not. Fechner deserves most of the credit for the concept of the sensory threshold and for detailing the various techniques for measuring it. A discussion of this cardinal concept may be found in his book Elemente der Psychophysik (1860), although the idea is actually of much earlier origins: Leibnitz and Herbart certainly spoke of it, and indeed it seems to have been considered even by ancient Greek philosophers. Methods for measuring the sensory threshold were known even before Fechner; his contribution was being the first to systematize and perfect them. It is for this reason that his book (Elemente) is considered basic.