Behavioral estimates of compression in normal and impaired ears

Abstract

Over the last 7 years, forward masking techniques have been used to estimate peripheral compression in the human auditory system. The growth of masking and temporal masking curve (TMC) techniques estimate the response to a tone at characteristic frequency (CF) by comparing the masking function (masker level as a function of signal level and masker-signal interval, respectively) for a masker at the signal frequency with the masking function for a masker below the signal frequency (assumed to be processed linearly at high CFs). Compression can also be estimated using the additivity of forward masking technique, in which the effects on signal threshold of combining two equally effective maskers are used to derive the exponent. Overall, the results suggest strong compression in humans (exponent of 0.2) across the range of CFs tested so far (250 to 8000 Hz). The behavioral techniques also suggest that a sensorineural hearing loss of greater than about 50 dB results in an almost complete linearization of the response. However, recent TMC data suggest that less severe hearing losses are associated with a reduction in gain, and a reduction in the level range over which compression is present, but no reduction in the maximum compression.