A direct comparison of active and passive amplification electrodes in the same amplifier system

Background: Active amplification electrodes are becoming more popular for ERP data collection, as they amplify the EEG at the scalp and thereby potentially decrease the influence of ambient electrical noise. However, the performance of active electrodes has not been directly compared with that of passive electrodes in the context of collecting ERPs from a cognitive task. Here, the performance of active and passive amplification electrodes in the same digitizing amplifier system was examined. Method: In Experiment 1, interelectrode impedance in an electrically quiet setting was manipulated to determine whether, in such recording conditions, active electrodes can outperform passive ones. In Experiment 2, the performance of active electrodes at the limits of natural skin impedance was explored, as was the relationship between active amplification circuitry and voltage stability in averaged EOG. Results: Results reveal a complex pattern of interrelations between electrode type, impedance, and voltage stability, indicating that which type of electrode is "best" depends non-trivially on the circumstances in which data are being collected. Comparison with existing methods: Traditional, passive electrodes acquired the cleanest data observed in any of the acquisition conditions at very low impedance, but not at any impedance >2. kΩ. Conclusion: Active electrodes perform better than passive ones at all impedances other than very low ones; however, this is qualified by the additional finding that during fast voltage fluctuations, such as those most desirable in most ERP studies, active electrodes are less able to accurately follow the EEG than passive ones.