Dual response audiometry: A time-saving technique for enhanced objective auditory assessment

The effectiveness of objective audiometric assessment can be improved by si multaneously recording transient evoked otoacoustic emissions (TEOAE) and a uditory brainstem responses (ABR). Using a stimulation paradigm based on se quences of linearly balanced click stimuli (as described by Kemp at al.(1)) acoustical and electrical responses of the auditory system can be obtained in one single run (dual response audiometry, DRA). The click stimuli are p resented via an ear canal probe containing a speaker and a miniature microp hone. EEG activity is recorded from surface electrodes fixed at the vertex and the mastoid ipsilateral to stimulus presentation. Microphone output and voltage difference between electrodes are fed into a dual-channel data acq uisition system, where they are separately amplified and filtered into appr opriate frequency ranges. After each stimulus, sweeps of 256 samples within a time window of 17 ms are taken of both signals. They are subject to arte fact rejection and averaging of amplitude and polarity. The electrical resp onses to low and high level clicks within one stimulus sequence are process ed separately, whereas the acoustical responses are summated across levels in order to eliminate stimulus-related contamination. As the result of one single run, ABR at two levels and non-linear TEOAEs are obtained within app roximately 1 min. The signal quality is estimated by correlation analysis a nd binomial statistics. Among various features of DRA, the most important a dvantage is the improvement of the success rate. The influence of perturbat ions is limited since muscle artefacts due to motor activity affect only th e ABR, whereas noise contamination affects only the TEOAE. The accuracy of threshold determination is better than with conventional ABR since the stim ulus level is measured in situ. One DRA examination provides complete infor mation about the functional integrity of the cochlea and neural pathways wi thout additional time. It appears ideal for the application as a second sta ge infant screen.