bci2000.org BBS

Hi, Dr. Schalk:

According to your document file, the ideal impedence should be about 10kΩ. However, in our experiment, sometimes the impedence is as high as 56kΩ. I know it is not good. But what will be the reason? We have used the gel and the hair of the subject is not very long. One cause I could think of is that the subject got a cold that day and had taken some medicine. Could this be a reason?

In my oppinion, the impedence should be as low as possible. But you say the ideal impedence should be about 10kΩ. Is that because of the physical property of human being?

Thanks.

Yueqing

According to your document file, the ideal impedence should be about 10kΩ. However, in our experiment, sometimes the impedence is as high as 56kΩ. I know it is not good. But what will be the reason? We have used the gel and the hair of the subject is not very long. One cause I could think of is that the subject got a cold that day and had taken some medicine. Could this be a reason?

The impedance gives a measure of conductivity between the electrodes and the scalp. While the signal quality depends on electrical noise in the room and also on the impedance, it is possible to have good signals with high impedance, or bad signals with low impedance. However, generally, you want impedances to be roughly below 10k. If you do not get impedances down, you may want to use a wooden stick, poke through the hole in the electrode, and try to push the hair on the scalp away. You may also want to use abrasive paste before you apply the electrodes and gel. I really suggest to consult somebody with EEG recording experience on this.

Gerv