SIGNAL PROPERTIES THAT REDUCE MASKING BY SIMULTANEOUS, RANDOM-FREQUENCY MASKERS

Large amounts of simultaneous masking can be produced by changing the frequency content of multicomponent maskers with each presentation Muc h of this masking appears to be informational, that is, produced by st imulus uncertainty. This study examined whether relatively simple chan ges in the properties or presentation mode of the signal could increas e the saliency of the signal and reduce this masking. The number of ma sker components varied from 2 to 100 across conditions. The reference signal was a 200-ms, 1000-Hz sinusoid, presented monaurally with the m asker. Across experiments, changes in masking relative to the referenc e condition were examined for different signal types (amplitude-modula ted, quasifrequency-modulated, or narrow-band noise), durations (100 o r 10 ms), and presentation modes (diotic, dichotic, or cross ear). The use of AM and NBN signals improved performance more consistently than the QFM signal, which degraded performance for some listeners. Lower masking in the reference condition for these listeners may have limite d the effects of signal type. Dichotic (versus monaural) presentation produced larger reductions in masking for more listeners and condition s. Comparisons to results with broadband maskers and other patterns in the data, however suggest the dichotic advantage may not clearly refl ect a reduction of masking due to uncertainty. Separating masker and s ignal onset/offset times by shortening signal duration produced the la rgest and most consistent reductions in masking produced by masker-fre quency uncertainty. (C) 1995 Acoustical Society of America.