Effects of Masker Envelope Fluctuations on the Temporal Effect.

Under certain conditions, detection thresholds in simultaneous masking improve when the onset of a short sinusoidal probe is delayed from the onset of a long masker. This improvement, known as the temporal effect, is largest for broadband maskers and is smaller or absent for narrowband maskers centered on the probe frequency. This study tests the hypothesis that small or absent temporal effects for narrowband maskers are due to the inherent temporal envelope fluctuations of Gaussian noise. Temporal effects were measured for narrowband noise maskers with fluctuating ("fluctuating maskers") and flattened ("flattened maskers") temporal envelopes as a function of masker level (Exp. I) and in the presence of fluctuating and flattened precursors (Exp. II). The temporal effect was absent for fluctuating narrowband maskers and as large as ~ 7 dB for flattened narrowband maskers. The AC-coupled power of the temporal envelopes of precursors and maskers accounted for 94 % of the variance in probe detection thresholds measured with fluctuating and flattened precursors and maskers. These results suggest that masker temporal envelope fluctuations contribute to the temporal effect and should be considered in future modeling efforts.