Abstract:

In experiment 1, masking patterns were obtained with an 80-dB SPL, 500-ms sinusoidally amplitude-modulated (SAM) masker (m=1.0). The 30-ms signal was centered at a masker peak or masker valley. Masker frequency (fm) was 750, 1350, or 2430 Hz; signal frequency (fs) was 0.8, 0.9, 0.95, 1.0, 1.2, 1.44, or 1.62 fm. Thresholds were generally higher for a signal at masker peak. The magnitude of this effect was governed by fs/fm, rather than by fs. In experiment 2, growth-of-masking functions (fm=1350 Hz, fs=1.44 fm) were measured for a SAM masker (m=0.5, 0.75, or 1.0). These thresholds were compared with those obtained with unmodulated maskers in forward or simultaneous masking. The comparisons suggest that thresholds for a signal at a peak of a SAM masker are due to simultaneous masking, while those in a valley are due primarily to forward masking when m=1.0 or simultaneous masking when m=0.5 or 0.75. Finally, the slope of the masking functions in simultaneous masking (unmodulated masker or signal at peak of SAM masker) changed from a slope greater than 2.0 to a slope of 1.0 at the highest levels; this will be discussed in terms of basilar membrane nonlinearity. [Work supported by NIDCD.]