Mid-bandwidth loudness depression in hearing-impaired listeners.

The loudness of a bandpass-filtered noise depends on its bandwidth. For bandwidths larger than a critical bandwidth, loudness increases as the bandwidth increases, an effect commonly referred to as spectral loudness summation. For bandwidths smaller than the critical bandwidth, it was shown recently for normal-hearing listeners that loudness decreases as the bandwidth increases. This study investigated if listeners with a hearing impairment of primarily cochlear origin also showed this effect. Levels at equal loudness between a 1500-Hz pure-tone reference and noise-band targets centered at 1500 Hz were measured for bandwidths in the range from 15 to 1620 Hz. The reference level was adjusted individually on the basis of the audiogram. The average level difference at equal loudness increased from 0 dB at 15 Hz up to a maximum of about 4 dB at 810 Hz. Thus, the mid-bandwidth loudness depression is also observed for hearing-impaired listeners.