Estimates of auditory filter shape using simultaneous and forward notched-noise masking

In this paper, we attempted to estimate the auditory filter shape using both simultaneous and forward masking experiments with notched-noise masker. In simultaneous masking experiment, masked threshold of the probe signal in the presence of a notched-noise masker were measured for five normal hearing subjects. In each trial, the level of the probe signal was varied while masker level was kept at a constant level. The frequencies of the probe signals were 0.5, 1.0, 2.0, and 4.0 kHz. The width and position of the notched-noise maskers were the same as in Glasberg and Moore (2000). In forward masking experiment, masked threshold were measured for six normal hearing subjects in similar notch conditions at the same frequencies, with the masker varied in the presence of a constant level of probe signal. The levels of probe signal were presented at 10, 20, and 30 dB above the absolute threshold of the subjects. A double roex auditory filter was then individually fitted to the data collected in these two experiments by the PolyFit procedure. ERB (Equivalent rectangular bandwidth) and the ratio of ERBs were calculated from these filters as measures to compare the tuning of the derived filters. The results suggest that the tuning of the auditory filters derived from the forward masking data was considerably sharper than those derived from simultaneous masking data. The tuning of the auditory filters becomes much sharper as the center frequency increases. However, the degree of sharpening of the tuning of the auditory filter by the forward masking data was not consistent at different center frequencies.