Quick question about bit 16 (High when new Epoch is started) in trigger status channel

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Kriale00
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Joined: Wed May 03, 2017 8:57 pm

Quick question about bit 16 (High when new Epoch is started) in trigger status channel

Post by Kriale00 » Tue Jan 14, 2020 9:19 pm

Hello,

I have a quick question about bit 16 (High when new Epoch is started) in trigger status channel. Is there any reason to not read from a bdf file an event that has bit 16 high? I am asking, because I noticed that the eeglab programmers discard any event that has this bit high (usually the first trigger, if recordings are not paused), but I don't understand why. I wrote my own code in matlab to read bdf data (following what described in https://www.biosemi.com/faq/trigger_signals.htm) and it seems to me that all the events should be read whether this bit 16 is high or low. When I use the bdf reader to check on the triggers, I see that the output is consistent with my code, but not with eeglab.

I just want to make sure I am not missing out anything important here.
Thank you.
Alex.

Coen
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Re: Quick question about bit 16 (High when new Epoch is started) in trigger status channel

Post by Coen » Tue Jan 14, 2020 10:43 pm

You are right, EEGLAB is wrong. The rising edge of the START EPOCH bit just indicates the start of an epoch after the recording was paused. The high-state duration of the START EPOCH bit has no meaning.

Best regards, Coen (BioSemi)

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