Effects of signal duration on the 500-Hz masking-level difference

Two experiments were conducted to study the masking-level difference (SoNo-S pi No thresholds) for 2-128-ms, 500-Hz tones in 32-dB pressure-spectrum level, continuous broadband noise. In Experiment 1 (N = 8) the Békésy tracking procedure was used, whereas in Experiment 2 (N = 3) an adaptive, two-interval forced-choice (2IFC) psychophysical procedure was used. The data from both experiments indicated that as the signal duration was shortened from greater than or equal to 100 to approximately 10 ms the SoNo and S pi No threshold integration functions diverged, thereby producing an increase in the masking-level difference. For signal durations less than 10 ms, however, the SoNo and S pi No threshold functions converged and the masking-level difference decreased. In Experiment 2, the mean masking-level difference decreased significantly by 1.7 dB as the signal duration was shortened from 10 to 2 ms. This new finding, which was not anticipated, has recently been confirmed in another laboratory (Cokely & Hall, 1985).