Denoising of Transient VEP Signals Using Wavelet Transform

Transient Visual Evoked Potential (TVEP) is an important diagnostic test for specific ophthalmologic and neurological disorders. TVEP investigation is focused on the dominant peaks N75, P100, N145, a negative deflection followed by a positive deflection and then a negative deflection. Quantification of these latency changes can contribute to the detection of possible abnormalities. We have applied the wavelet denoising method to 100 pre-recorded signals using all the available wavelets in MATLAB wavelet toolbox to analyze the peaks (P100, N75 and N145). From the results it is clear that the positive peak is clearer in the denoised version of the signal using the wavelets Sym5 and Bior3.5. As opposed to the previous studies however our study clearly shows that the output using the former wavelet effectively brings out the P100 when compared to the latter. The first negative peak was clear in the denoised version of the signal using the wavelets Bior5.5 Bior6.8 and coif4. The second negative peak N145 was clear using all the above wavelets. In conclusion all the three peaks were fairly clear in the denoised output using the wavelet sym7. This would greatly help the medical practitioners. All the previous studies concentrated on the P100 only. Using the proposed method all three peaks could be analyzed in detail.