The discovery that expectancy and payoff have such a dramatic influence upon detection behavior was incorporated into a new theoretical conception of the detection situation. Tanner and Swets (1954) proposed that statistical decision theory and certain ideas about electronic signal-detecting devices might be used to build a model closely approximating how people actually behave in detection situations. The model is called the theory of signal detection (TSD) and is described in detail by Green and Swets (1966). Fundamental to TSD is the concept of noise.