#Electrode eeg skin#

The goal of the present study was to provide a quantitative evaluation of the effects of electrode impedance on the S/N ratio of ERP recordings by an independent laboratory with no significant ties to manufacturers of EEG recording equipment 1. (2001) simply recorded the resting EEG and assessed the power in different frequency bands as a function of impedance. There are several published papers describing the properties and performance of these systems ( Ferree, Luu, Russell, & Tucker, 2001 Metting van Rijn, Peper, & Grimbergen, 1990 Tucker, 1993), but these papers do not provide direct, empirical, and quantitative comparisons of low and high electrode impedances under the conditions of a typical ERP experiment. However, it is not clear whether the S/N ratio will actually be meaningfully reduced when high electrode impedances are used in conjunction with an EEG recording system that was designed to tolerate these high impedances (which we will call high-impedance systems). If, for example, the S/N ratio of the raw EEG recording is half as great with high electrode impedances as with low electrode impedances, then it would be necessary to record four times as many trials with high electrode impedances as with low electrode impedances to achieve the same S/N ratio and hence the same statistical power in the averaged ERPs (all else being equal). However, the increased number of trials required for this is often higher than one might expect, because the S/N ratio of an average does not increase linearly with the number of trials in the average but instead increases with the square root of the number of trials (see Luck, 2005).

In most cases, researchers would like to maintain the probability of obtaining a significant effect.

To put this in terms that reflect the вЂњbottom lineвЂќ for most ERP researchers, recording the EEG under conditions that yield a lower S/N ratio will either decrease the probability of obtaining a statistically significant experimental effect (if the number of trials is held constant) or increase the amount of recording time necessary to obtain a significant effect (if the statistical power is held constant). That is, a decline in the S/N ratio of the EEG recordings will necessitate an increase in the number of trials tested in each subject or an increase in the number of subjects tested in an experiment to achieve a given S/N ratio in the averaged ERPs. If the S/N ratio of the EEG is lower, more trials will need to be averaged together to obtain a given S/N ratio in the averaged ERPs. The goal of the present study was to determine whether the S/N ratio is meaningfully reduced when the EEG is recorded with high compared to low electrode impedances. High electrode impedances do not meaningfully reduce the size of the EEG signal ( Johnson et al., 2001), but they might increase the noise level, resulting in a lower signal-to-noise (S/N) ratio. These systems have become quite popular, but many researchers are concerned that the quality of the EEG will be poorer with high electrode impedances than with low electrode impedances. When large numbers of electrodes are used, however, the process of reducing the impedances becomes very time consuming, and this has led manufacturers of electroencephalogram (EEG) recording systems to develop systems that can tolerate high electrode impedances.

#Electrode eeg skin#

In event-related potential (ERP) studies, researchers have traditionally minimized noise in the recordings by reducing the impedance between the recording electrodes and the living skin tissue ( Luck, 2005 Picton et al., 2000).