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ACOUSTICS2008/2818 Two-tone suppression of stimulus frequency otoacoustic emissions in human ears with sensorineural hearing loss

Two-tone suppression (2TS) of stimulus frequency otoacoustic emissions (SFOAEs) recorded in normalfunctioning human ears is a non-invasive measure of cochlear nonlinearity. This study investigates 2TS SFOAE response properties in 63 subjects with sensorineural hearing loss and normal middle-ear function. SFOAEs were measured using tones at frequencies (f p) from 0.5 to 8 kHz and levels from 40-60 dB SPL. For interpreting SFOAEs, hearing status was classified at each frequency according to degree of hearing loss, with losses ranging from within normal limits to 95 dB HL. SFOAE suppression was measured as a function of suppressor frequency (f s) and level (Ls), with results analyzed in terms of a SFOAE suppression tuning curve. A tip-to-tail dierence (TTD) was defined between the Ls needed to produce a criterion decrement in SFOAE level at f s one octave below f p and the Ls needed to produce a criterion decrement near f p. The TTD estimates cochlear-amplifier gain in normal-functioning ears, but its properties in impaired ears based on SFOAEs have not been examined. Results will be analyzed as a function of the hearing status to assess the relative impact of outer-hair cell dysfunction in the SFOAE source region at tonotopic place. [Work supported by NIH.]