It is necessary to eliminate the shifting resting potential (mean value) from the signal, but this DC shift varies with time. To avoid this problem, an AC differential amplifier with a high pass filter with cut-off at 0.05 Hz and relatively long time constant can be used. Also the amplifier should have a high gain (gain of about 1000) to amplify the captured signals.
The drifts can be reduced by careful application of the Ag/AgCl-electrodes and filling them bubble free with electrode-gel. Technical improvement in EOG amplifiers can reduce the influence of drifts as well.
Dependency on changes in luminance can be eliminated by reference compensation and repeated calibration.
The influence of EMG artifacts can be reduced by instructing the subject to keep mouth open and avoid innervations of the mimic musculature. Dependency on changes in CRP can be eliminated by reference compensation and repeated calibration.
Conduct the experiments in the same environment on same time of the day (same lighting conditions) to avoid the effects by the difference in luminance level.
Try to place the electrodes on the same location (on the face) for all the participants (minute changes can even change the signal level)Conduct the experiments in the same environment on same time of the day (same lighting conditions) to avoid the effects by the difference in luminance level.
Always clean the skin with cotton to minimise the variations in skin resistance.
Next post will be on the analysis and the selection of of electrodes.
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