Determination of primary features of ABR signals in intelligent system aiding the auditory system diagnosis BUŁKA J., WOCHLIK I., KOWAL J., BANIA P., IZWORSKI A. Department of Automatics AGH University of Technology Al. Mickiewicza 30, 30-059 Kraków, POLAND Abstract: - The paper presented below contains description of a research study concerning an automated system for objective diagnosis of the human auditory system. In the paper selected aspects have been presented, concerning the detection of characteristic features of ABR signals. Attention has been particularly focused on the detection of those signal parameters, which are most important for the auditory system diagnosis. The paper contains a detailed description of the preliminary processing of ABR signals, as well as the determination of waves I, III and V and their respective latency periods. The presented work should be treated as the first stage in the process of construction of a fully automated, thus objective, system for aiding the diagnostic process, performed by the [medical] staff of audiological institutions. Key-Words: - ABR Signals, Biomedical Engineering, Human-Machine Systems, Signal Processing 1. Introduction The auditory brainstem response (ABR) signals are electrical signals of brain activity (EEG), which are generated as a response to an acoustic stimulus. At present they are the basis for the most objective methods of studying the human auditory abilities. The methods is applied particularly in the cases, when the application of classical audiometric methods is difficult or impossible, as the examinations of infants and young children. Time dependence of a typical ABR signal contains five up to seven waves, denoted by roman numbers I to VII, registered within 10 ms from the occurrence of the acoustic stimulus. In the clinical evaluation of the ABR signals many various parameters, mainly related to the wave V, are taken into account, e.g. the latency period of wave V, the I-IV time distance, absence of some waves, particularly wave V, the amplitude ratio of wave V and wave I [3]. Diagnosis of hearing damages, using the registration of the ABR signals, is based on the analysis of the recording morphology and latency periods of particular waves. The second criterion seems to be much more convenient for formulation as a set of simple rules, which provide a way to check whether a given recording can be classified as a regular one. At present it has been accepted, that the latency periods of particular waves should be contained within the limits, determined in the tests of large number of people with normal hearing abilities. However the determination of the above mentioned limits, with the nonzero probability of error occurrence, requires measurements for large number of samples, what in turn calls for automation of the process of maxima determination in the ABR signals (Fig.1). Because of the considerable individual variety, high level of low-frequency noise and the occurrence of muscular artifacts, the task of latency period determination (localization of the maximum in the ABR recording) for a given wave becomes complicated, particularly for the small amplitudes of the activating signal (< 50 dB). For these cases it is very easy to take a noise bump or an accidental artefact for a real wave and vice versa. Up to date no characteristic features have been defined, which would allow, as for the ECG case, a precise localization of the parameters of particular waves. The scheme proposed below is an attempt of automation for the process of latency period determination for particular waves and it is a results of a heuristic treatment, based on the analysis of large number of samples.