Further Beneficial Effect of Hearing Aids on Speech Recognition Performance Besides Amplification: Importance of the Restoration of Symmetric Hearing

Objective:To identify the improvement in auditory spectral resolution, temporal resolution, and speech recognition conferred with various hearing-aid (HA) technologies when the amplification effect of the HA is excluded, and to compare the beneficial effects depending on the restoration of symmetric hearing with different amplification settings in various hearing impairment conditions.Study Design:Prospective study.Setting:Tertiary referral center.Subjects:Sixty-two subjects who had used HAs for more than 3 months were divided into four groups: group 1, bilateral HAs (n=28); group 2, unilateral HA in the better ear (n=12); group 3, unilateral HA in the worse ear (n=12); group 4, unilateral HA with symmetric hearing thresholds (n=10).Methods:Aided performance and unaided performance were compared in each group. Four different psychoacoustic measurements were made: 1) spectral ripple discrimination; 2) temporal modulation detection; 3) speech recognition threshold in white noise; and 4) speech discrimination score (SDS) under quiet conditions. All test signals were presented by a loudspeaker located 1 m in front of the subject in a sound-attenuating booth, at their most comfortable levels, with or without HAs.Results:In group 1, the use of HAs significantly improved both SDS under quiet conditions and speech recognition in noise compared with the unaided condition. Group 2 showed better SDS under quiet conditions with HAs, and group 3 showed improved speech recognition in noise with HAs. In contrast, in group 4, no measurements differed with or without HAs.Conclusions:These results demonstrate the benefits of HAs on speech perception in noise, in addition to their amplification effect, but only when HA restores symmetric hearing.