This study tested the hypothesis that suppression contributes to the difference between simultaneous masking ͑SM͒ and forward masking ͑FM͒. To obtain an alternative estimate of suppression, distortion-product otoacoustic emissions ͑DPOAEs͒ were measured in the presence of a suppressor tone. Psychophysical-masking and DPOAE-suppression measurements were made in 22 normal-hearing subjects for a 4000-Hz signal/ f 2 and two masker/suppressor frequencies: 2141 and 4281 Hz. Differences between SM and FM at the same masker level were used to provide a psychophysical estimate of suppression. The increase in L 2 to maintain a constant output ͑L d ͒ provided a DPOAE estimate of suppression for a range of suppressor levels. The similarity of the psychophysical and DPOAE estimates for the two masker/suppressor frequencies suggests that the difference in amount of masking between SM and FM is at least partially due to suppression.

Aided consonant and vowel identification was measured in 13 listeners with high-frequency sloping hearing losses. To investigate the influence of compression-channel analysis bandwidth on identification performance independent of the number of channels, performance was compared for three 17-channel compression systems that differed only in terms of their channel bandwidths. One compressor had narrow channels, one had widely overlapping channels, and the third had level-dependent channels. Measurements were done in quiet, in speech-shaped noise, and in a three-talker background. The results showed no effect of channel bandwidth, neither on consonant nor on vowel identification scores. This suggests that channel bandwidth per se has little influence on speech intelligibility when individually prescribed, frequency-varying compressive gain is provided.

Slopes of forward-masked psychometric functions (FM PFs) were compared with distortion-product otoacoustic emission (DPOAE) input/output (I/O) parameters at 1 and 6 kHz to test the hypothesis that these measures provide similar estimates of cochlear compression. Implicit in this hypothesis is the assumption that both DPOAE I/O and FM PF slopes are functionally related to basilar-membrane (BM) response growth. FM PF-slope decreased with signal level, but this effect was reduced or reversed with increasing hearing loss; there was a trend of decreasing psychometric function (PF) slope with increasing frequency, consistent with greater compression at higher frequencies. DPOAE I/O functions at 6 kHz exhibited an increase in the breakpoint of a two-segment slope as a function of hearing loss with a concomitant decrease in the level of the distortion product (L(d)). Results of the comparison between FM PF and DPOAE I/O parameters revealed only a weak correlation, suggesting that one or both of these measures may provide unreliable information about BM compression.

This study examined the time course of cochlear suppression using a tone-burst suppressor to measure decrement of distortion-product otoacoustic emissions (DPOAEs). Seven normal-hearing subjects with ages ranging from 19 to 28 yr participated in the study. Each subject had audiometric thresholds 15 dB HL [re ANSI (2004) Specifications for Audiometers] for standard octave and inter-octave frequencies from 0.25 to 8 kHz. DPOAEs were elicited by primary tones with f 2 ¼ 4.0 kHz and f 1 ¼ 3.333 kHz (f 2 /f 1 ¼ 1.2). For the f 2 , L 2 combination, suppression was measured for three suppressor frequencies: One suppressor below f 2 (3.834 kHz) and two above f 2 (4.166 and 4.282 kHz) at three levels (55, 60, and 65 dB SPL). DPOAE decrement as a function of L 3 for the toneburst suppressor was similar to decrements obtained with longer duration suppressors. Onset-and setoff-latencies were 4 ms, in agreement with previous physiological findings in auditory-nerve fiber studies that suggest suppression results from a nearly instantaneous compression of the waveform. Persistence of suppression was absent for the below-frequency suppressor (f 3 ¼ 3.834 kHz) and was 3 ms for the two above-frequency suppressors (f 3 ¼ 4.166 and 4.282 kHz).