Comparative study of several Fir median hybrid filters for blink noise removal in Electrooculograms

The presence of a kind of impulsive noise due to eye blinks is typical during the acquisition of electrooculograms. This paper describes a comparative study of several algorithms used to remove the blink noise in the electroculogram preserving the sharp edges in the signal produced by the so-called saccadic eye movements. Median filters (MF) and several types of Fir Median Hybrid Filters (FMH) have been analyzed. Two types of real electrooculogram register with saccadic movements in controlled position were used to test the performance of the pre-processing filters (sampling rate 20Hz). The filtered signals were later processed with a saccadic eye movement detector algorithm in order to detect changes in the sensitivity and positive predictive value. The results show that neither FMH filters nor WFMH filters produce better results than median filters, in this particular study. The highest averaged values of sensitivity and positive predictive value are obtained by using a median filter of length I=6 samples (S=96.22%, V++=95.42%) and the variant SWFMH of the same length (S=96.27%, V++=91.91%). Although the differences in detection rates are not meaningful between these filters, median filters obtain slightly higher rates of saccades detection than SWFMH, but a reduction in computational burden is obtained by using FHM variants.