Frequency resolution at equivalent sound‐pressure levels in normal‐hearing and hearing‐impaired listeners

Abstract

Forward‐masked psychophysical tuning curves (PTCs) were obtained for multiple‐level 1000‐Hz probe tones from 15 normal‐hearing and 23 hearing‐impaired ears with cochlear hearing loss. Comparisons between normal‐hearing and hearing‐impaired PTC characteristics were made at equivalent masker levels near the tips of PTCs. The low‐frequency slopes of PTCs from hearing‐impaired listeners were not different from those of normal‐hearing listeners, i.e., hearing‐impaired listeners did not demonstrate abnormal upward spread of masking when equivalent masker levels were compared. Only 8 of the 23 hearing‐impaired listeners demonstrated abnormally broad PTCs, due exclusively to abnormally gradual high‐frequency slopes to their PTCs. This demonstration of abnormal downward spread of masking was only observed in listeners with hearing losses greater than 40 dB HL. From these results, it would appear that some, but not all, cochlear hearing losses greater than 40 dB HL influence the sharp tuning capabilities usually associated with outer hair‐cell function. The restriction of abnormal findings in this study to the high‐frequency sides of PTCs alone is likely due to the use of equivalent masker‐level comparisons, and also to the use of flat‐envelope nonsimultaneous maskers rather than fluctuating‐envelope simultaneous masker. [Work supported by NINCDS.]