Frequency masking patterns and “excess masking” in normal-hearing and hearing-impaired listeners

Abstract

The presence of “excessive upward spread of masking” in high-frequency sensorineural hearing-loss (HFSNHL) subjects has been previously demonstrated by other investigators. This excess masking, defined by predictions from a “noise” model of hearing loss, occurs in the transition region between normal and impaired hearing. To examine this phenomenon further, frequency masking patterns (FMPs) were obtained from two normal-hearing subjects and one HFSNHL subject. Using a 200-Hz narrow-band noise (NBN) masker (90 dB SPL) with an upper edge at 520 Hz, FMPs from the impaired ear demonstrated excess masking, which it was hypothesized might be explained by an inability to “listen in the valleys” of the masker envelope because of poor temporal resolution. To test this notion, the experiment was repeated using a 40-Hz NBN masker (90 dB SPL), which has less rapid envelope fluctuations. No differences in the upward spread of masking were seen between the 200- and 40-Hz bandwidth-equal SPL maskers. When the experiment was repeated with equal spectrum level maskers, the 40-Hz NBN masker produced less upward spread of masking in both normal-hearing and hearing-impaired ears. These data suggest that, for the HFSNHL subject, excessive upward spread of masking cannot be completely explained by an inability to “listen in the valleys.” [Work supported by NINCDS.]