General characteristics and suppression tuning properties of the distortion-product otoacoustic emission 2f₁-f₂ in the barn owl

The distortion-product otoacoustic emission (DPOAE) 2f₁-f₂ was measured in the ear canal of the barn owl. DPOAE were elicited by primary tones in 11 frequency regions from 1 to 9 kHz. The highest DPOAE output levels and best thresholds were found for f₁ frequencies of 4 to 7 kHz and additionally at the lowest f₁ frequency investigated. In some cases, the DPOAE sound pressures were only 37 dB below the primary-tone levels (PTL). The optimal primary-tone frequency ratios ranged from 1.05 to 1.45 and varied strongly among the different frequency regions investigated. The largest optimal ratios were measured in the middle frequency range for f₁. At lower and higher f₁, the optimal ratios decreased. DPOAE levels could be suppressed in a frequency-selective way by adding a third tone. As in other non-mammals, the best suppressive frequencies were near f₁, suggesting DPOAE generation near the frequency place of this primary tone. This is in contrast to what is known for mammalian species, where the DPOAE is thought to be generated near f₂. To obtain 6 dB of suppression of the DPOAE level, suppressor-tone levels ranging from 13 dB below to 4 dB above the primary- tone level were necessary. The Q(10dB)-values of suppression tuning curves increased as a function of frequency up to a value of 15.8. This tendency resembled the increase in frequency selectivity of auditory nerve fibers in this species.