Noise reduction is the process of removing a signal that is not needed, that is, removing unwanted perturbation of a signal. Usually noise comes at a high frequency so it's more likely that you'd need low-pass filters in an EOG system in order to block higher frequencies. A low pass filter is a filter that passes low frequency signals but attenuates signals with frequencies higher than the determined cutoff frequency. The cutoff frequency is the limit in the frequency response at which the energy flowing through the system begins to be attenuated.