The fluctuating-masker benefit for normal-hearing and hearing-impaired listeners with equal audibility at a fixed signal-to-noise ratio

Abstract

While normal-hearing (NH) listeners demonstrate better speech intelligibility for fluctuating-masker than for stationary-noise conditions, hearing-impaired (HI) listeners generally show little or no fluctuating-masker benefit (FMB). This result has been interpreted in terms of suprathreshold deficits (e.g., reduced spectral or temporal resolution or distorted stream-segregation cues) that limit “dip-listening.” However, reduced FMB for HI listeners might instead be attributable to audibility limitations or to differences between the signal-to-noise ratios (SNRs) at which NH and HI listeners are tested. This study examined this issue by equalizing stationary-noise performance to allow measurements at a common SNR, equalizing audibility, and presenting identical signals to pairs of NH and HI listeners. Audibility was equalized using linear gain, low-pass filtering (4 kHz) and intensity filtering to remove speech-signal elements below the HI audiometric threshold. Nonsense-syllable identification performance in stationary noise was equalized by adjusting the response set size. Stationary-noise trials (adapting set size) were interleaved with fluctuating-masker trials (adapting SNR), ensuring stable stationary-noise performance throughout the test. Fluctuating maskers included low- and high-rate modulated noise, speech-modulated noise, and an interfering-talker condition. Results were assessed to determine whether and under which conditions the HI listeners demonstrated reduced FMB not attributable to SNR or audibility effects.