Spectro-temporal modulation transfer function (STMTF) for various types of temporal modulation and a peak distance of...

For noise which is spectrally modulated (ripple noise) as well as temporally modulated (the ripples move), the Spectro-Temporal Modulation Transfer Function (STMTF) is defined as the curve relating modulation threshold to temporal modulation frequency with ripple spacing as a parameter. A white noise stimulus was spectro-temporally modulated in the 0.2- to 1.0-kHz region with a spectral modulation frequency (peak distance) of 0.2 kHz. Three types of temporal modulation were applied: the ripples rolled upward, downward, or the peaks and troughs interchanged periodically. It is shown that the STMTFs for these types are equal. So, for a ripple spacing of 0.2 kHz the spectro-temporal modulation thresholds are independent of the type of temporal modulation. These STMTFs appeared to be low-pass functions, no minimum was found. Their plateaus were at the same modulation depth as the modulation thresholds found by previous investigators who employed stationary ripple noise.