Application of Velocity Filters to Somatosensory Evoked Potential Measurements for Removal of Stimulus Artifact

In this paper, velocity filtering is applied to somatosensory evoked potential (SEP) measurements to remove the stimulus artifact (SA). Using an array of electrodes, velocity information is used as a criterion for discerning the SEP from the SA. The SEP is known to propagate at speeds below 100 m/s due to nerve physiology, whereas the SA propagation mode is electromagnetic, and propagates near the speed of light. The velocity filtering method is presented, with spatial frequency resolution, physical array implementation, filter realization, and trace-to-trace consistency of the measurements identified as factors that influence overall performance. SEP data from the median nerve were recorded using an 11 channel array at the wrist, with stimulation at the index finger. These data are used to assess the velocity filtering method. The filter output is analyzed qualitatively showing a visual improvement in the SEP measurement when compared against the filter input. It is concluded that the SNR gain of the filter is promising, but distortion in the SEP estimate may occur due to spatial frequency resolution and trace-to-trace inconsistencies in the measurements