Previous work suggests that, for some listeners, masker fluctuation may be advantageous for NoS pi detection. This study tested the hypothesis that the benefit of masker fluctuation to binaural analysis is based on the ability to take advantage of epochs of low masker energy in the fluctuating masker where the cues underlying binaural signal detection are more salient. The hypothesis was evaluated using the time-domain version of COSS analysis derived by Buus et al. [J. Acoust. Soc. Am. 99, 2288-2297 (1996)] which measures the perceptual weight applied by a listener within a relatively brief time window as a function of the masker level during the window. The results indicated a dependency of signal detection on short-term masker level in the NoS pi condition but not in the NoSo condition. This finding supports a new perspective indicating that binaural signal detection depends upon the envelope of a masker in a way that is fundamentally different from that typically associated with monaural detection.