Predicting frequency selectivity in forward masking from simultaneous masking

Abstract

Measures of frequency selectivity from forward masking indicate sharper tuning than those from simultaneous masking (Houtgast, 1974; Moore, 1978). We show that a simple relation between forward and simultaneous masking predicts this result. Consider the masking of a 10-ms, sinusoidal signal of frequency fs = 2.0 kHz by a 200-ms, 50-Hz-wide narrow-band noise masker with center frequency fm. Let Df = fm − fs be the frequency interval between the signal and the masker, and let Dt = ts − tm be the time interval between their offsets. We may define the following three masking conditions: (1) on-frequency forward, Dt = 15 ms, Df = 0 Hz, (2) off-frequency simultaneous, Dt = 0 ms, Df = 200 Hz, and (3) off-frequency forward, Dt = 15 ms, Df = 200 Hz. Masking functions (signal intensity at masked threshold versus masker intensity) were obtained in each of these conditions. Our preliminary data indicate that the off-frequency forward masking function (F) is predicted reasonably well by the composite relation F = G(kH), where G is the on-frequency forward masking function, H is the off-frequency simultaneous masking function, and k is a constant. Predictions were equally as good for other values of Df, yielding the expected difference in tuning between simultaneous and forward measures.