Poster Session I: Comparison of tripolar and traditional electrodes: Waveform morphology.

The waveforms of visual evoked potentials (VEPs) recorded by tripolar electrodes are different from those recorded by traditional electrode arrays. Traditional arrays record potentials using both an active and a reference electrode. The location of this reference will affect the waveform amplitude and shape. Conversely, tripolar electrodes measure the surface Laplacian across three concentric rings housed within a single electrode surface. These differences may influence the morphology of evoked responses. We compared these two modalities by recording pattern-reversal VEPs to two sizes of checkerboard. Visual inspection of the VEPs suggest that the signals recorded by the tripolar system have attenuated higher frequencies and increased latency of the major waveform components. Root-mean-square comparison of the two signal types confirm attenuation at the higher frequencies in the tripolar recording. Additionally, there is a cumulative delay present within both the large and small check conditions, such that each subsequent component recorded by the tripolar electrodes is shifted increasingly later in time compared to the same components recoded by the traditional electrodes. Such latency shifts may be indicative of a difference in the physiological sources that are measured by the two EEG systems.