Concurrent measurement of distortion product otoacoustic emissions and auditory steady state evoked potentials

Distortion product otoacoustic emissions (DPOAEs) and auditory steady state evoked response potentials (ASSRs) can both be evoked by tone pairs with frequencies f(1) and f(2). The DPOAE is maximal at 2f(1)-f(2) and the ASSR is maximal at f(2)-f(1). Since DPOAE magnitude depends on the ratio f(2)/f(1), but ASSR amplitude depends on the beat frequency f(2)-f(1), compromises are necessary when recording both responses concurrently. Tone pairs with f(2) of 900, 1800 and 3600 Hz were presented simultaneously at either 40 or 50 dB sound pressure level (SPL). The f(1) frequency of each pair was approximately 85 or 180 Hz lower than f(2). Phase measurements were used to calculate apparent latencies at 40 dB SPL. For increasing f(2), DPOAE latencies were 14.5, 9.7 and 6.3 ms for 85 Hz beats, and 11.5, 9.0 and 4.3 ms for 180 Hz beats. ASSR latencies were 22.0, 15.7 and 17.8 ms at 85 Hz, and 17.7, 11.3 and 9.6 ms at 180 Hz. From a model of the mechanical transmission in the cochlea, delays between the basilar membrane and the generator of the ASSR were estimated as 15.4, 12.2 and 15.3 ms at 85 Hz and 8.6, 7.6 and 8.0 ms at 180 Hz.