Masking by modulated and unmodulated noise: Effects of bandwidth, modulation rate, signal frequency, and masker level

Abstract

The threshold for a sinusoidal signal masked by a band of noise is often times lower when the masking noise is modulated than when it is unmodulated. The difference in masked thresholds is referred to as the modulated-unmodulated difference, or MUD. These present experiments examined the effects of masker bandwidth, masker rate, and masker level on the MUD at several different signal frequencies. The MUD generally increased with increasing masker bandwidth; for masker bandwidths wider than a critical band (or an equivalent rectangular bandwidth-ERB), the results may be influenced by across-channel processes underlying comodulation masking release. The MUD for an ERB masker (MUDERB) was influenced less by masker rate than was the MUD for a broadband (BB) masker (MUDBB). The MUDERB and especially the MUDBB increased significantly with increasing masker level when the modulated masker was modulated at a depth (m) of 1.0, but not when it was modulated at a depth of 0.75. These results have significant implications for extending the MUD paradigm to hearing-impaired subjects. Finally, the MUDERB and the MUDBB increased with increasing signal frequency. This effect for the ERB masker is largely (if not completely) due to the wider absolute bandwidths at higher frequencies. The effect with the BB masker may be influenced by differences in the magnitude of suppression across frequency.

Comodulation Enhances Signal Detection via Priming of Auditory Cortical Circuits

“…If true, this could explain differences in the size of within- and across-channel CMR. Within-channel configurations produce behavioral CMR several times larger than across-channel CMR (Carlyon et al, 1989; Bacon et al, 1997; Verhey et al, 2003). Likewise, Nelken et al (1999) observed locking suppression (decreased noise representation) at very low SNRs.…”

Modeling comodulation masking release using an equalization cancellation mechanism

“…A number of experimental conditions have been investigated in previous CMR studies, which have not been considered directly in the present study. These studies investigated in much more detail effects of signal frequency ͑e.g., Moore, 1987͒, masker spectral width ͑Haggard et al, 1990;masker spectral level ͑Moore andShailer, 1991;Bacon et al, 1997;Cohen, 1991;Hall, 1986;McFadden, 1986͒, the influence of the envelope statistic of the masker modulator ͑e.g., Eddins and Wright, 1994;Grose and Hall, 1989;Hicks and Bacon, 1995͒, the effect of modulation frequency and modulation depth ͑Car-lyon and Stubbs, 1989;Hall et al, 1996;Lee and Bacon, 1997;Bacon et al, 1997;Verhey et al, 1999;Eddins, 2001͒, effects of flanking band number and flanking band level ͑e.g., Hatch et al, 1995;Schooneveldt and Moore, 1987͒ and other effects. The current version of the model does not include a nonlinear peripheral filtering stage and therefore cannot account for level-dependent cochlear compression and effects associated with it such as level-dependent frequency tuning and suppression.…”

Extracting binaural information from simultaneous targets and distractors: Effects of amplitude modulation and asynchronous envelopes

“…One potential explanation for this result is that the target is at a higher sensation level and may be more detectable in the presence of modulated distractors than among unmodulated distractors, given that a pure tone is more detectable in a modulated masker than in an unmodulated masker ͑the socalled modulated-unmodulated difference, or MUD; Carlyon et al, 1989;Bacon et al, 1997͒. Perhaps increasing the detectability of the target ͑and so increasing its sensation level͒ in the presence of distractors makes its ITD more separable and reduces thresholds.…”