Abstract 1010, Date 1:00 pm, Sunday, February 5, 2006 (24 hours) Session D3: Otoacoustic Emissions
Hybrid DPOAE/ASSR Measurements Using a Modified DPOAE Stimulus Setting
Thomas Janssen, Johann Oswald, Thomas Rosner
Distortion product otoacoustic emissions (DPOAEs) and auditory steady state responses (ASSRs) both provide frequency specific and quantitative assessment of hearing capability. The high discrepancy in recording time (seconds for a DPOAE, minutes for an ASSR) arises the question: why wasting time, why not recording DPOAEs during ASSR measurements? The present study therefore addressed the question whether ASSRs and DPOAEs can be recorded simultaneously using a modified DPOAE stimulus setting in which one of the primary-tone is amplitude-modulated. DPOAEs of frequency 2f1–f2 and ASSRs of modulation frequency 40 Hz were measured in 10 normal hearing subjects at test frequency f2 between 0.5 and 8 kHz (f2/f1=1.2). Additionaly, 80 Hz ASSR were measured binauraly with two tone pairs per ear. Primary-tone f2 was amplitude-modulated for eliciting ASSR. Primary-tone level L2 was fixed (54 dB SPL) whereas primary-tone level L1 was varied between 54 and 75 dB SPL for searching for the optimal primary-tone level ratio at which DPOAE level was highest. Average decrease in DPOAE level was 2.60 dB SPL (SD=1.38 dB) that one in ASSR amplitude 1.83 dB SPL (SD=2.38 dB) for the 40 Hz ASSR and 2.36 dB (SD=2.91 dB) for the 80 Hz ASSR, respectively, when comparing single and hybrid mode. ASSR amplitude considerably decreased for L1 exceeding 69 dB SPL. Findings suggest simultaneous DPOAE and ASSR measurements to be feasible at primary-tone levels of up to 65 dB SPL. For compensating loss in amplitude and thus yielding single mode test quality, recording time has to be increased. However, longer recording time is only necessary at close-to-threshold responses where the signal-to-noise ratio is low. The advantage of a DPOAE stimulus setting in which one of the primary tone is amplitude- modulated over a stimulus setting with un-modulated tones is that optimal stimulation and thus maximum response amplitudes can be reached independent on test frequency for both ASSRs and DPOAEs.