Comparing two proposed measures of cochlear mechanical filter bandwidth based on stimulus frequency otoacoustic...

It has been hypothesized that the sharpness of the cochlear mechanical filter is related to two measures based on stimulus frequency otoacoustic emissions (SFOAEs). The first is the group delay of the SFOAE; the second is the bandwidth of the SFOAE two-tone suppression isoinput tuning characteristic. A corollary of this is that natural variability in cochlear mechanical bandwidth within a population would lead to a positive correlation between these two SFOAE-based measures of tuning within that population. To test this prediction, SFOAE group delay and SFOAE two-tone suppression isoinput tuning characteristics were measured in a sample of 16 audiometrically normal subjects. Contrary to the prediction, no statistically significant correlation was found between the two bandwidth measures. Cochlear model simulations were used to aid the interpretation of this result. These suggested that a positive correlation between the two measures is expected, but that it may well be too weak to detect with the given sample size, due to the influence on the SFOAE measures of random inhomogeneities in basilar membrane impedance.