A comparison of three distortion product otoacoustic emission input/output function procedures to estimate cochlear sensitivity in dogs

The purpose of the present study was to determine which of three distortion product otoacoustic emission (DPOAE) input/output (I/O) procedures would elicit minimum response levels (MRLs) at the lowest primary signal levels. DPOAE I/O functions were recorded from six dogs with presumed normal hearing as determined by auditory brainstem response, otoscopy, tympanometry, ipsilateral acoustic-reflex thresholds, and DPOAEs. The procedures (P1, P2, and P3) used to determine DPOAE MRLs at the lowest levels of the primary signals (L1 and L2) were:

P1) Equal level primary signals that were increased in level together (L1 = L2).

P2) Higher frequency primary signal fixed 10 dB lower in level than lower frequency primary signal and both increased together in level (L1 = L2 + 10 dB).

P3) Lower frequency primary was fixed at 65 dB with the higher frequency primary signal increased in level (L1 = 65 dB SPL; L2 varied). A second purpose was to determine the level of correlation between DPOAE detection threshold and the slope of corresponding DPOAE I/O functions. Statistical analysis revealed the lowest MRLs were obtained with P2. Using P1 and P3 the average MRLs were 13 dB and 3 dB higher respectively. The mean I/O function slope was 0.75 at 2000 Hz and 1.0 at 4000 Hz but they were not significantly different. Further research using P2 is proposed to correlate MRL measures with degree of cochlear hearing loss.