Prevalence of excess binaural broadband loudness summation in the hearing-impaired population and implications for hearing aid gain targets

Previous studies reported large individual differences in binaural broadband loudness summation in hearing-impaired listeners after narrowband loudness was normalized. These differences in loudness perception might require substantial fine-tuning for some hearing aid users to provide acceptable loudness in daily use. The present study aims at characterizing binaural broadband loudness summation for a hearing-impaired population, the prevalence of higher-than-normal values, and the potential implications for hearing aid target gains. For 180 hearing-impaired participants we measured standard audiological diagnostic parameters, binaural broadband loudness summation and computed gain targets according to NAL-NL2, DSLm[i/o] and trueLOUDNESS, a prescriptive procedure that includes individual loudness measurements. The observed binaural broadband loudness summation of the hearing-impaired participants was, on average, 13 dB higher and showed a higher variance relative to a normal-hearing reference group. In about 40% of all participants a binaural broadband loudness summation was beyond the normal-hearing range. The average excess loudness summation appears to be included in established prescriptive procedures, while relevant differences to trueLOUDNESS gain targets were observed in more than half of the participants. Elevated binaural broadband loudness summation appears to be a prevalent and individual trait in the hearing-impaired population and its assessment might be useful for individualized hearing aid fitting.