Monaural and binaural frequency selectivity in hearing-impaired subjects

Sensorineurally hearing-impaired (HI) subjects often report difficulties in complex acoustical environments. To investigate whether these problems arise from specific deficits in the frequency selectivity in binaural listening conditions, thresholds were measured for a 500-Hz sinusoid in phase (So) or antiphase (Spi) masked by a diotic notched noise (No). The equivalent rectangular bandwidth (ERB) for filters derived from diotic (NoSo) and dichotic (NoSpi) threshold curves is larger for the HI subjects than for the normal-hearing (NH) subjects. However, the ratio of binaural to monaural ERB is the same. The data indicate that there is no additional retrocochlear impairment reducing the binaural frequency selectivity of HI subjects. A specific binaural impairment was also tested by measuring the perception of binaural pitch (Huggins' pitch). Two out of eight HI subjects failed to perceive this pitch, although in the masking experiment they obtained a binaural masking-level difference of up to 10 dB. The current data therefore provide no clear evidence for a specific binaural impairment factor in hearing impairment that deteriorates several aspects of binaural processing in a similar way.