Abstract:

There is a strong link between the discrimination of small phase changes in highly peaked harmonic complexes and the sensation level of the stimuli. This relationship may stem from a differential ability across listeners to code dynamic amplitude changes within waveform periods. To test this hypothesis, growth of masking was measured for flat-amplitude harmonic complexes varying in phase structure and level. Maskers were constructed with odd harmonics in cosine phase and all even harmonics shifted in phase from 0 to 90 degrees. Masked thresholds were measured for a 5-ms Hanning-windowed probe centered either at the primary peak of the masker waveform or at a secondary peak near the midpoint of the period. Growth-of-masking functions when the probe is placed at the primary waveform peaks are generally linear. However, in normal-hearing listeners, masking of probes placed at the secondary peaks grows more nonlinearly. Reduced masking observed at low stimulus levels may be related to compression of the high-amplitude primary peaks which act as forward maskers. Differential forward-masking by the large primary peaks across listeners with normal hearing and those with hearing impairment will be related to the ability to discriminate complexes with differing phase structures. [Work supported by NIH.]