Spectral loudness summation as a function of duration for hearing-impaired listeners.

Spectral loudness summation was measured for 10- and 1000-ms long bandpass-noise signals with bandwidths in the range of 0.2 to 6.4 kHz centered at 2 kHz for nine listeners with hearing impairment of primarily cochlear origin. Loudness matches between signals with the same duration and different bandwidth were obtained using an adaptive two-interval, two-alternative forced-choice procedure with interleaved tracks. The 3200-Hz wide reference signal had a level of 45 dB or 65 dB SPL. Every signal was individually frequency equalized prior to presentation in order to ensure audibility of all spectral components for the two reference input levels. Generally the same amount of spectral loudness summation for 10- and 1000-ms long signals was obtained for both reference levels. However, some hearing-impaired listeners show, similarly to normal-hearing listeners, a larger spectral loudness summation for short than for long duration signals, indicating that duration effects in spectral loudness summation are caused by retrocochlear processes.