With the theory of signal detectability as a framework, two psychophysical experiments were conducted in which each observation interval was well defined for the listener. Each interval contained noise, and it either did or did not (p=0.5) contain a signal (1000 cps, 0.5 sec in duration). In separate sessions of the first experiment, either the listener gave a yes‐no decision or he responded with a rating (1–4) after each observation interval. Operating characteristics were obtained with E/N 0 equal to 15.8. It is clear from the data that the trained listener can perform as well when he adopts the multiple criteria necessary for the rating method as when he adopts the single criterion required by the binary‐decision procedure. In the second experiment, only the rating method was used to determine the relation between d′ and E/N 0. The resulting function, for d′ ⩽ 3.0, approximates straight line which passes through the origin and which has nearly the same slope as that obtained in other laboratories.