Masked thresholds for hearing-impaired listeners

Abstract

Masked thresholds for sinusoids between 1000–500 Hz in (1) broadband noise, (2) low-pass filtered noise, and (3) high-pass filtered noise were measured by adaptive forced-choice procedure for hearing-impaired listeners [acute Meniere disease (n = 3), noise-induced hearing loss (n = 7), and eighth-nerve tumor (n = 2)]. Thesholds in the filtered noises were measured as a function of masker cutoff frequency. Masker spectrum levels (55–70 dB SPL) were listener dependent and were equal for the three masker conditions. Masked thresholds for the broadband masker were near normal except for the tumor patients, who showed abnormally large (by 10–15 dB) masked thresholds at 1000 Hz. Auditory filters were estimated by plotting the masked thresholds for the low-pass and high-pass marker conditions at the marker cutoff frequencies. Linear functions were fitted to the masked thresholds to derive the auditory filter's half-power frequencies and bandwidth. The auditory filters were characterized by shifts in the center frequency of the filter below signal frequency and, often, by broad tuning. [Work supported by NIH.]