Loudness as a cue for acceptable noise levels.

Abstract

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). 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. 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. 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.