The observer's responses to aural signals in noise are compared to the output of an electronic detection system whose constants are intended to be close to those of the human auditory detection system.Of the four variations of an electronic detector tested, the best correlation between the detector and the observer occurred for signals of duration 0. 3 second, band pass 60 cps (single tuned RLC circuit), square law detector, output filter time constant, 0.15 second.The incomplete correlation between the signal responses of the observer and the detector can be explained by assuming that the observer's threshold fluctuates randomly about a mean value with a dispersion of about 20% of the mean, or alternatively that there is internal noise with this dispersion generated inside the observer's detection system.The observer's false alarms appear to be caused by noise fluctuations (as measured by the electronic detector) of the same average magnitude and dispersion as those calculated for a detector with the same threshold fluctuation. However, the observer's false alarm rate is about an order of magnitude lower than that calculated for the fluctuating threshold detector so it is clear that the model is deficient in some important respects.