Generation of distortion product otoacoustic emissions in infants with a combined air and bone conduction stimulus

Objectives: Evaluation of Distortion Product Otoacoustic Emissions (DPOAEs) by combining Air Conduction (AC) and Bone Conduction (BC) stimuli in infants.Methods: Measurements were performed in 19 normal hearing infants, and in 23 adults serving as a control group. The stimulus consisted either of two AC tones, or of combined AC/BC tones. DPOAEs were measured for f2 at 0.7, 1, 2, 4 kHz, and a constant ratio of f2/f1 = 1.22. Sound pressure level of the primary stimulus L1 was held constant at 70 dB SPL, while the level of L2 was decreased in 10 dB steps from 70 to 40 dB SPL. A response was included for further analysis when DPOAEs reached a Signal to Noise Ratio (SNR) of & GE;6 dB. Additional DPOAE responses of <6 dB SNR were included when visual inspection of the measurements indicated clear DPOAEs. Results: DPOAEs could be elicited in infants at 2 and 4 kHz for the AC/BC stimulus. DPOAE amplitudes evoked by the AC/AC stimulus were larger than those by the AC/BC stimulus, with the exception of 1 kHz. The highest amplitudes of DPOAEs were registered for a stimulation level of L1 = L2 = 70 dB, with the exception of AC/AC at 1 kHz, where the highest amplitudes were with L1-L2 = 10 dB. Conclusions: We demonstrated that DPOAEs can be generated in infants by a combined AC/BC stimulus at 2 and 4 kHz. The high noise floor needs to be further reduced to achieve more valid measurements in frequencies <2 kHz.