Offset in the trigger code read by EEGLab
Posted: Wed May 03, 2017 9:11 pm
Hello,
I am using the TDT system to send triggers to Biosemi. I set up the TDT digital port to work with 16 bits, so that should work for biosemi. I also selected all the 16 trigger lines + OR in Biosemi, even though I believe this option really affects only the online average and not what is recorded in the BDF file. The triggers are read and displayed correctly by Biosemi. However, when I try to open the BDF file with the code that I found in EEGLab, the trigger code is off by a factor of 3840, which I believe is caused by Biosemi enabling 4 additional bits. In other words, if I send a trigger code = 4, I should expect to have the following bits: 0000 0000 0000 0100, while in fact I get the following bits: 0000 0111 1000 0000. Well, at least this is the conclusion that I came up with when I tried to recreate 3840 with bits and based on what I read online from other people having trigger offset problems. In the past I used Biosemi with the Presentation software to deliver the triggers and then I opened the bdf files with the same EEGLab function that I am using now and I never had this problem.
Can you please advise if there is anything that I should be changing in the Biosemi configuration file or if you think this is a bug in the matlab code that I am using?
Thank you.
Alex.
I am using the TDT system to send triggers to Biosemi. I set up the TDT digital port to work with 16 bits, so that should work for biosemi. I also selected all the 16 trigger lines + OR in Biosemi, even though I believe this option really affects only the online average and not what is recorded in the BDF file. The triggers are read and displayed correctly by Biosemi. However, when I try to open the BDF file with the code that I found in EEGLab, the trigger code is off by a factor of 3840, which I believe is caused by Biosemi enabling 4 additional bits. In other words, if I send a trigger code = 4, I should expect to have the following bits: 0000 0000 0000 0100, while in fact I get the following bits: 0000 0111 1000 0000. Well, at least this is the conclusion that I came up with when I tried to recreate 3840 with bits and based on what I read online from other people having trigger offset problems. In the past I used Biosemi with the Presentation software to deliver the triggers and then I opened the bdf files with the same EEGLab function that I am using now and I never had this problem.
Can you please advise if there is anything that I should be changing in the Biosemi configuration file or if you think this is a bug in the matlab code that I am using?
Thank you.
Alex.