Measurement and modeling of binaural loudness summation for hearing-impaired listeners.

The summation of loudness across ears is often studied by measuring the level difference required for equal loudness (LDEL) of monaural and diotic sounds. Typically, the LDEL is ∼5-6 dB, consistent with the idea that a diotic sound is ∼1.5 times as loud as the same sound presented monaurally at the same level, as predicted by the loudness model of Moore and Glasberg [J. Acoust. Soc. Am. 121, 1604-1612 (2007)]. One might expect that the LDEL would be <5-6 dB for hearing-impaired listeners, because loudness recruitment leads to a more rapid change of loudness for a given change in level. However, previous data sometimes showed similar LDEL values for normal-hearing and hearing-impaired listeners. Here, the LDEL was measured for hearing-impaired listeners using narrowband and broadband noises centered at 500 Hz, where audiometric thresholds were near-normal, and at 3000 or 4000 Hz, where audiometric thresholds were elevated. The mean LDEL was 5.6 dB at 500 Hz and 4.2 dB at the higher center frequencies. The results were predicted reasonably well by an extension of the loudness model of Moore and Glasberg.