Effects of masker envelope coherence on intensity discrimination

Masked detection threshold for a pure tone signal depends on the coherence of masker envelope fluctuation across frequency, with lower thresholds for coherent fluctuation under some conditions. The benefit of coherent masker modulation is larger for detection than for suprathreshold tasks, such as pure tone intensity discrimination [Hall, J. W. and Grose, J. H. (1995). J. Acoust. Soc. Am. 98, 847-852]. In the present study, sensitivity to increments in signal intensity was measured for a 1000-Hz signal, either a tone or a 20-Hz-wide narrowband noise. In one set of conditions the masker was one or more bands of noise, each 20 Hz wide, and in another set of conditions the masker was a single 1620-Hz-wide band of Gaussian noise or noise multiplied by the envelope of a 20-Hz bandpass noise. Coherent masker envelope fluctuation improved detection thresholds in all conditions. Intensity discrimination for a tonal standard in comodulated noise was elevated for standard levels near detection threshold and improved with increasing signal-to-noise ratio, whereas performance was uniformly poor across level for the noise standard. Results are most consistent with the interpretation that the reduced benefit of coherent masker modulation in suprathreshold intensity discrimination is due to the disruptive effects of envelope fluctuation.