Strange looking drifts through all channels
Posted: Mon Apr 06, 2009 6:04 pm
My collegue and I just started recording eegs for our thesis and have run into some problems with Biosemi. The first few recordings went very well, but in all but one of the last five sessions we had some major problems with odd-looking drifts. We have come to our wits end.
We have low off-sets for all electrodes, CM is in range, eeg looks beautifully (visually) – but every so often (and unfortunately quite often) we have a drift that through all electrodes and the whole screen – it is like one big solid line – this is usually followed by another drift right after. Our computer technician advised us that it probably has something to do with the cms- or drl-electrode because the drift goes through all channels - like I said, it is a solid line. We tried taping the cms- and drl-cable to the headcap – so we can avoid unnecessary pulling on the cable when our subject moves. The Cm- in range-light does not come off or flicker during the drifts at all.
We don’t know what else to do. We had one good 4-hour-recording this morning and ran into the same problems again this afternoon.
Any suggestions? Problem-solutions? Has this ever happened to anyone?
Thanks a lot!
Julia
We have low off-sets for all electrodes, CM is in range, eeg looks beautifully (visually) – but every so often (and unfortunately quite often) we have a drift that through all electrodes and the whole screen – it is like one big solid line – this is usually followed by another drift right after. Our computer technician advised us that it probably has something to do with the cms- or drl-electrode because the drift goes through all channels - like I said, it is a solid line. We tried taping the cms- and drl-cable to the headcap – so we can avoid unnecessary pulling on the cable when our subject moves. The Cm- in range-light does not come off or flicker during the drifts at all.
We don’t know what else to do. We had one good 4-hour-recording this morning and ran into the same problems again this afternoon.
Any suggestions? Problem-solutions? Has this ever happened to anyone?
Thanks a lot!
Julia