Abstract
Analog and digital filters are commonly used in recording and analyzing event-related potentials (ERPs). However, an inadvertent application of filter can considerably distort the ERP waveforms. This paper presents basic knowledge on how filters work and how they affect signals represented in the time domain. After a brief introduction of analog and digital filters, the following three common misconceptions about filtering are addressed : (1) filtered waveforms do not include signals below or above the cutoff frequency; (2) any high-pass filter can be described in terms of the time constant; and (3) zerophase filters do not distort the waveforms. None of these three propositions are true. Finally, this paper makes some recommendations for the use of filters in ERP research. (Japanese Journal of Physiological Psychology and Psychophysiology, 26 (3) : 237-246, 2008.)
