Speech recognition in background noise: monaural versus binaural listening conditions in normal-hearing patients

Patients with unilateral conductive hearing impairment often experience a great advantage in improved hearing thresholds after reconstructive ear surgery because the binaural hearing leads to increased speech recognition in competing noise. The aim of this study was to develop a clinical audiometric test to quantify the ability of speech recognition in background noise preoperatively and postoperatively.

A model consisting of phonetically balanced (PB) monosyllabic words and/or a just-follow-conversation test (JFC) was used in 16 normal-hearing listeners. In 8 of the participants, JFC at two levels of background noise (60 and 40 dB sound pressure level) was used as the only method. The tasks were performed in an anechoic chamber with varying spatial separations of speech and noise sources under free field conditions. The tests were made binaurally and monaurally; the latter condition was achieved by occluding one ear with a hearing protector. In PB word tests, the percent of correctly repeated words was scored. In the JFC task, the speech signal was adjusted by the listener to a level where he or she could just understand what was being said. This was expressed as a signal-to-noise (S/N) ratio.

In both types of tests, the subjects achieved significantly better speech recognition scores in the binaural situations. In summary, compared with monaural conditions, the subjects achieved 17% to 18% better speech recognition in PB tests, and in JFC tests a 2-to 3-dB lower S/N ratio in binaural conditions.

These free field tests can be developed further as a clinical tool preoperatively and postoperatively to evaluate the effect of binaural hearing after ear surgery.