BioSemi.nl

Hello,

We have recently purchased a 64-channel BioSemi system. We have 8 'hangdowns' (to record EOG) as well. Can you give me some information on how these 8 sensors work?

Specifically, if I apply two on the mastoids, two under the eyes, two on the temples and two on the nose- does it matter which sensors go where (i.e. which number hangdown goes where)? I am assuming the only thing that matters here is that the sensors are placed in pairs- i.e. if I have hangdown EX3 on the left mastoid, I should have hangdown EX4 on the right mastoid. Is this correct?

Otherwise, do you have advice as to where I should place the 8 electrodes?

The flat-type electrodes with touchproof connectors are all identical. It does not matter which electrode is connected to which EX input, and they can be located anywhere on the body.

The ActiView display of bipolar combinations is just a software choice (by modifying the LabVIEW code, any other combination can be displayed). The 8 EX channels are saved to file in monopolar form (with respect to CMS), and any combination can be constructed during referencing off line, see http://www.biosemi.com/faq/cms&drl.htm).

For example: in order to display the headcap channels with respect to a linked ear reference, you should select the two EX channels connected to the ears (or mastoids) in the "reference" selection box (ActiView will subtract the average of the two EX channels from the headcap channels). The same procedure should be repeated during off-line review (because the data is always saved to file unreferenced).

Best regards, Coen (BioSemi)