Digital filter for eye-movement signals

Electro-oculography (EOG) is widely used in research and clinical laboratories because it provides a noninvasive method for recording the full range of eye movements during testing of saccades, pursuit, optokinetic and vestibular systems. As the bandwidth of the recorded signal is usually below 60 Hz, the ideal signal conditioner would be a low-pass filter with high attenuation at the frequency of the interference. This dual filtering task is usually performed by two separate filters cascaded to achieve the low-pass and notch filter properties. In this technical note, the authors describe a single filter which has both characteristics, and derive new design equations which allow one to specify the low-pass characteristics and the notch frequency.