SFOAE input/output functions elicited by slightly off-frequency suppressors

Abstract

Basilar membrane (BM) response growth is thought to be related to stimulus frequency otoacoustic emission (SFOAE) input/output (I/O) functions. SFOAEs comprise the response to sinusoidal excitation and provide an estimate of nonlinearity at a tonotopic place on the BM. SFOAE I/O functions at frequency f0 (across levels L0) are measured in the presence of suppressor fs (at level Ls) in subjects with normal hearing. fs is varied below, equal to, and above f0 in the range 0.93<fs/f0<1.07. For fixed suppressor level (Ls=80 dB SPL) and varying L0<Ls, the SFOAE I/O function is predicted to be closely related to the BM I/O function. Measured I/O functions are approximately invariant as fs is varied. Functions saturate at increasing levels with a decrease in some ears at the highest levels. An alternative paradigm in which Ls=L0 are covaried yields SFOAE I/O functions with local minima, but which may have a less direct connection to BM response growth. Based on primaries at fs and f0, SFOAE and DPOAE I/O functions differ. One implication is that SFOAE I/O functions may be used to relate BM nonlinear response growth to perceptual processes, including loudness growth and forward masking. [Work supported by NIH (R01 DC003784, T32 DC00013).]