Loudness summation across ears for hearing-impaired listeners

Abstract

The summation of loudness across ears is often studied indirectly by measuring the level difference required for equal loudness (LDEL) of monaurally and diotically presented sounds. Typically, the LDEL is 5–6 dB, consistent with the idea that a diotic sound is about 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 smaller than 5–6 dB for hearing-impaired listeners, because loudness recruitment leads to a greater change of loudness for a given change in level. However, previous data from several laboratories showed similar LDEL values for normal- and hearing-impaired listeners. Here, the LDEL was measured for normal-hearing and hearing-impaired listeners using narrowband and broadband noises centered on a frequency where the latter had near-normal audiometric thresholds (500 Hz) and at a frequency where audiometric thresholds were elevated (3000 or 4000 Hz). The LDEL was similar for the two center frequencies for the normal-hearing listeners, but was smaller at the higher center frequency for the hearing-impaired listeners. The results were predicted reasonably well by the loudness model of Moore and Glasberg.