Speech Intelligibility as a Cue for Acceptable Noise Levels

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.

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.

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.

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.