Measuring with 2 different electrode sets

[cmuehl]

Hi,

We purchased a second 32 electrode set two years after we bought our old one. Using both to measure with 64 electrodes (in saline solution) results in 2 clearly distinguishable groups of electrode signals on the ActiveView screen. The impression is that the amplitudes are larger for the new set.

1. Is there some explanation for that (e.g. slow decay of the old electrodes over 2 years of usage)?

2. After the referenceing by CAR those differences seem (at least visually) attenuated. This IMO is due to the (far-away and all electrode affecting) noise that constitutes the biggest part of the signal. With real data, recorded from participants, this averaging procedure should not make the difference it made with the saline recording. Right?

3. However, how critical could those differences in sensitivity be when it comes to the analysis stage? With respect to the left/right distribution of A and B sets in the BIOSEMI 64 electrode setup there would be a left/right difference in amplitude and therefore every measure comparing relations between different (left vs right) electrodes might be compromised.

Thank you for your patience. I am looking forward to your answers.

Best,
Christian Mühl

[Coen]

Old electrodes may produce more (low frequency) noise than newer ones.

Electrode wear cannot significantly influence signal amplitude. You can easily check this with a "two bucket test", as described in the guidelines for use of the ActiveTwo system.

In other words: you may encounter differences in signal-to-noise ratio between the sets. This is due to differences in noise level, and not due to differences in signal amplitude.

Best regards, Coen (BioSemi)

[cmuehl]

Thanks for the quick reply. I will try the two bucket test as you suggest.

Best regards,
Christian