Review raw file problem: Flat channels in BST but NOT in EEGLAB

Discussions
1

Hi,

I encountered a weird problem when viewing the raw file for a subject. I have three different recordings for each subject (resting state, task 1, task 2), and for a specific subject when I do “Review raw file”, one of the three recordings is completely flat (with a channel, PO8, that shows a weird behavior). This is a snapshot of the raw data: https://imgur.com/a/l9WcOUv

What is weird is that when I recorded that data everything was fine. Plus, when viewing the same data with EEGLAB, the program correctly imports the data. So the problem is not in the data but in the process of importing it in BST (which is up-to-date). The EEG system I used to record data is Brain Products, ActiCap system.

I have never encountered such problem. I copied again the raw file and imported it again, multiple times. Nothing changes.

What are your suggestions?
Thanks

2

PO8 seems to show weird, strong signals. Because BST adjusts the amplitude scale automatically, this probably masks the data on the other channels. You can either declare this channel as bad or change the amplitude scale manually.

3

I already tried doing that but nothing changed, unfortunately. That was my first thought too.

4

Can you post a 2D plot of some sensor data topography, please?

5

Hi Simone,

Signals are not flat, but one channel is incorrectly classified as EEG (PO8). It has values that are much higher than all the others, which causes a wrong vertical scaling for all the channels.

Change the type of PO8 manually (right-click on channel file > Edit channel file) or mark it as bad, and it should solve your problem.

Francois

6

Hi Francois,

PO8 is not incorrectly classified as EEG, it is an active EEG channel in my 64 channel montage (of which 3 are used for eye movements and one for the right earlobe for off-line re-referencing to linked earlobes, not shown in the plot I linked of course).

As I said to Sylvain as well, I already tried to mark it as a bad channel and change the plot scale, but nothing changed.

I’d like to stress the fact that, during the recording, albeit the impedence of PO8 was higher than the other channels, the recording was fine, it didn’t have a behavior that justifies thinking it as obscuring all the other channels. But I nevertheless already tried excluding PO8, as I said.

Thanks.

7

Hi.

I’ll do it as soon as I import the BST database in my laptop.

8

Hi everyone,

Indeed it’s as I initially thought and as you suggested: PO8 has a strong signal and covers everything else. I tried again marking PO8 as bad, I found out I just had to close the raw so that BST saved the bad channels info, I reopened it and now it’s ok.

Sorry, didn’t think that I first had to close the raw window to save.

Thanks again.

1 Like
9

All is well then. Thanks for the feedback!