Amplitude‐discrimination performance is found to be independent of the duration of the signals to be discriminated for durations ranging from 20 to 200 msec provided that the ratio of signal energy to noise‐power density is kept constant. If the ratio of signal energy to noise‐power density is manipulated by altering either the noise‐power density or the signal duration, then discrimination performance is also independent of that ratio once it exceeds 20 dB. The implication of these findings is discussed.