Preferences for digital noise reduction and microphone mode settings in hearing-impaired listeners with low and high tolerances for background noise.

Objective: To examine whether people with low and high acceptable noise levels (ANLs) have different preferences for aggressiveness of noise reduction (NR) and microphone mode, and whether they get different noise tolerance benefit with these two features.Design: Participants completed laboratory tests of unaided ANL and aided modified ANLs (with speech fixed at two levels) and preferences (at two SNRs) while listening to four levels of NR, three microphone modes and four combinations of NR/directionality.Study sample: Twenty adults with hearing loss; 10 with low ANLs and 10 with high ANLs.Results: Seven individuals with low ANLs and 10 individuals with high ANLs preferred the maximum NR setting; the remaining three individuals with low ANLs had inconsistent preference for NR. Eight people in each ANL group preferred the maximum directional setting (broadband (BB) directionality), the remaining two people in each group had inconsistent preferences for microphone mode.Conclusions: Because most participants preferred the maximum NR and directionality settings, ANLs could not be used to differentially prescribe these hearing aid settings.

Speech Intelligibility as a Cue for Acceptable Noise Levels.

OBJECTIVES: The goal of this study was to examine whether individuals are using speech intelligibility to determine how much noise they are willing to accept while listening to running speech. Previous research has shown that the amount of background noise that an individual is willing to accept while listening to speech is predictive of his or her likelihood of success with hearing aids. If it were possible to determine the criterion by which individuals make this judgment, then it may be possible to alter this cue, especially for those who are unlikely to be successful with hearing aids, and thereby improve their chances of success with hearing aids. DESIGN: Twenty-one individuals with normal hearing and 21 with sensorineural hearing loss participated in this study. In each group, there were 7 with a low, moderate, and high acceptance of background noise, as determined by the Acceptable Noise Level (ANL) test. (During the ANL test, listeners adjusted speech to their most comfortable listening level, then background noise was added, and they adjusted it to the maximum level that they were "willing to put up with" while listening to the speech.) Participants also performed a modified version of the ANL test in which the speech was fixed at four different levels (50, 63, 75, and 88 dBA), and they adjusted only the level of the background noise. The authors calculated speech intelligibility index (SII) scores for each participant and test level. SII scores ranged from 0 (no speech information is present) to 1 (100% of the speech information is present). The authors considered a participant's results to be consistent with a speech intelligibility-based listening criterion if his or her SIIs remained constant across all of the test conditions. RESULTS: For all but one of the participants with normal hearing, their SIIs remained constant across the entire 38-dB range of speech levels. For all participants with hearing loss, the SII increased with speech level. CONCLUSIONS: For most listeners with normal hearing, their ANLs were consistent with the use of speech intelligibility as a listening cue; for listeners with hearing impairment, they were not. Future studies should determine what cues these individuals are using when selecting an ANL. Having a better understanding of these cues may help audiologists design and optimize treatment options for their patients.

Loudness as a cue for acceptable noise levels.

BACKGROUND/PURPOSE: The acceptable noise level (ANL) test is the only test that is known to predict success with hearing aids with a high degree of accuracy. A person's ANL is the maximal amount of background noise that he or she is "willing to put up with" while listening to running speech. It is defined as the speech level minus the noise level, in decibels (dB). People who are willing to put up with high levels of background noise are generally successful hearing-aid wearers, whereas people who are not willing to put up with high levels of background noise are generally unsuccessful hearing-aid wearers. If it were known what cues that listeners are using to decide how much background noise they are willing to tolerate, then it might be possible to create technology that reduces these cues and improves listeners' chances of success with hearing aids. As a first step toward this goal, this study investigated whether listeners are using loudness as a cue to determine their ANLs. Research Design and Study Sample: Twenty-one individuals with normal hearing and 21 individuals with sensorineural hearing loss participated in this study. In each group of 21 participants, 7 had a low ANL (<7 dB), 7 had a mid ANL (7-13 dB), and 7 had a high ANL (>13 dB). DATA COLLECTION/ANALYSIS: Participants performed a modified version of the ANL in which the speech was fixed at four different levels (50, 63, 75 and 88 dBA), and participants adjusted the background noise (multitalker babble) to the maximal level at which they were willing to listen while following the speech. These results were compared with participants' equal-loudness contours for the multitalker babble in the presence of speech. Equal-loudness contours were measured by having the participants perform a loudness-matching task in which they matched the level of the background noise (multitalker babble), played concurrently with speech, to a reference condition (also multitalker babble). During the test condition, the speech played at 50, 63, 75, or 88 dBA. All testing was performed in a sound booth with the speech and the noise presented from a loudspeaker at a 0° azimuth, 3 feet in front of the participant. Each condition was presented multiple times, and the results were averaged. Presentation order was randomized. Participants were tested unaided. RESULTS: Participants' ANLs were compared with their equal-loudness contours for the background noise. ANLs that ran parallel to the equal-loudness contours were considered consistent with a loudness-based listening strategy. This pattern was observed for only two participants - both hearing-impaired. CONCLUSIONS: The majority of listeners showed no consistent trend between their ANLs and their loudness-matched data, suggesting that they are using cues other than loudness to determine their ANLs. ANLs were consistent with loudness-matched data for a small subset of listeners, suggesting that they may be using loudness as a cue for determining their ANLs.

The effect of presentation level on normal-hearing and hearing-impaired listeners' acceptable speech and noise levels.

BACKGROUND: Acceptable noise level (ANL) is a measure of the maximum amount of background noise that a listener is willing to "put up with" while listening to running speech. This test is unique in that it can predict with a high degree of accuracy who will be a successful hearing-aid wearer. Individuals who tolerate high levels of background noise are generally successful hearing-aid wearers, whereas individuals who do not tolerate background noise well are generally unsuccessful hearing-aid wearers. PURPOSE: Various studies have been unsuccessful in trying to relate ANLs to listener characteristics or other test results. Presumably, understanding the perceptual mechanism by which listeners determine their ANLs could provide an understanding of the ANL's unique predictive abilities and our current inability to correlate these results with other listener attributes or test results. As a first step in investigating this problem, the relationships between ANLs and other threshold measures where listeners adjust the signal-to-noise ratio (SNR) according to some criterion in a way similar to the ANL measure were examined. RESEARCH DESIGN AND STUDY SAMPLE: Ten normal-hearing and 10 hearing-impaired individuals participated in a laboratory experiment that followed a within-subjects, repeated-measures design. DATA COLLECTION AND ANALYSIS: Participants were seated in a sound booth. Running speech and noise (eight-talker babble) were presented from a loudspeaker at 0°, 3 ft in front of the participant. Individuals adjusted either the level of the speech or the level of the background noise. Specifically, with the speech fixed at different levels (50, 63, 75, or 88 dBA), participants performed the ANL task, in which they adjusted the level of the background noise to the maximum level at which they were willing to listen while following the speech. With the noise fixed at different levels (50, 60, 70, or 80 dBA), participants adjusted the level of the speech to the minimum, preferred, or maximum levels at which they were willing to listen while following the speech. Additionally, for the minimum acceptable speech level task, each participant was tested at four participant-specific noise levels, based on his/her ANL results. To emphasize that the speech level was adjusted in these measurements, three new terms were coined: "minimum acceptable speech level" (MinASL), "preferred speech level" (PSL), and "maximum acceptable speech level" (MaxASL). Each condition was presented twice, and the results were averaged. Test order and presentation level were randomized. Hearing-impaired participants were tested in the aided condition only. RESULTS: For most participants, as the presentation level increased, SNRs increased for the ANL test but decreased for the MinASL, PSL, and MaxASL tests. For a few participants, ANLs were similar to MinASLs. For most test conditions, the normal-hearing results were not significantly different from those of the hearing-impaired participants. CONCLUSIONS: For most participants, stimulus level affected the SNRs at which they were willing to listen. However, a subset of listeners was willing to listen at a constant SNR for the ANL and MinASL tests. Furthermore, for these individuals, ANLs and MinASLs were roughly equal, suggesting that these individuals may have used the same perceptual criterion for both tests.

Using average correction factors to improve the estimated sound pressure level near the tympanic membrane.

BACKGROUND: Sound pressure-based real ear measurements are considered best practice for ensuring audibility among individuals fitting hearing aids. The accuracy of current methods is generally considered clinically acceptable for frequencies up to about 4 kHz. Recent interest in the potential benefits of higher frequencies has brought about a need for an improved, and clinically feasible, method of ensuring audibility for higher frequencies. PURPOSE: To determine whether (and the extent to which) average correction factors could be used to improve the estimated high-frequency sound pressure level (SPL) near the tympanic membrane (TM). RESEARCH DESIGN: For each participant, real ear measurements were made along the ear canal, at 2-16 mm from the TM, in 2-mm increments. Custom in-ear monitors were used to present a stimulus with frequency components up to 16 kHz. STUDY SAMPLE: Twenty adults with normal middle-ear function participated in this study. INTERVENTION: Two methods of creating and implementing correction factors were tested. DATA COLLECTION AND ANALYSIS: For Method 1, correction factors were generated by normalizing all of the measured responses along the ear canal to the 2-mm response. From each normalized response, the frequency of the pressure minimum was determined. This frequency was used to estimate the distance to the TM, based on the » wavelength of that frequency. All of the normalized responses with similar estimated distances to the TM were grouped and averaged. The inverse of these responses served as correction factors. To apply the correction factors, the only required information was the frequency of the pressure minimum. Method 2 attempted to, at least partially, account for individual differences in TM impedance, by taking into consideration the frequency and the width of the pressure minimum. Because of the strong correlation between a pressure minimum's width and depth, this method effectively resulted in a group of average normalized responses with different pressure-minimum depths. The inverse of these responses served as correction factors. To apply the correction factors, it was necessary to know both the frequency and the width of the pressure minimum. For both methods, the correction factors were generated using measurements from one group of ten individuals and verified using measurements from a second group of ten individuals. RESULTS: Applying the correction factors resulted in significant improvements in the estimated SPL near the TM for both methods. Method 2 had the best accuracy. For frequencies up to 10 kHz, 95% of measurements had <8 dB of error, which is comparable to the accuracy of real ear measurement methods that are currently used clinically below 4 kHz. CONCLUSIONS: Average correction factors can be successfully applied to measurements made along the ear canals of otologically healthy adults, to improve the accuracy of the estimated SPL near the TM in the high frequencies. Further testing is necessary to determine whether these correction factors are appropriate for pediatrics or individuals with conductive hearing losses.