Median averaging of auditory brain stem responses

Objective: The primary aim of this study is to demonstrate the feasibility of acquiring auditory evoked potentials (AEPs) by median averaging and stud y its performance under various recording conditions. The auditory brain st em response (ABR) was used as the AEP of choice because it has the poorest signal to noise ratio (SNR) with inherent high susceptibility to extraneous noise. Secondary aim is to evaluate the characteristics of the median ABRs in comparison with the conventional mean averaged ABRs. Design: Single sweep responses to clicks obtained from four subjects at 5 d B steps were saved in hard disk and used for off-line mean and median avera ging. The characteristics of the median averaging technique were investigat ed by manipulating the averaging procedure using the same set of single swe ep recordings and comparing them with the mean averaged responses. The effe cts of analog to digital input resolution (bit size) was simulated computat ionally by increasing quantization. Results: The results showed that AEPs with low SNRs such as the ABR can be successfully acquired using median averaging with about the same number of sweeps as was required for mean averaging, provided the EEG signal is digit ized with a high number of bits. The resulting waveform generally contained more identifiable waves than the corresponding mean average and had a high -frequency noise superimposed on it. This high-frequency noise was successf ully filtered out using a digital, running mean smoothing filter. The media n average showed an advantage over the mean average when occasional artifac ts were recorded. Conclusion: The results showed that ABRs can be acquired successfully by me dian averaging provided EEG is digitized with high bit size. Compared with conventional mean averaging, median averaging is less sensitive to infreque nt, externally and internally generated noise that plagues conventional tec hniques and may help improve wave identification.