[Eeglablist] Triggers issues

[Alex Lepauvre]

Dear All,

We are currently having an issue with the response triggers of our
experiment. It is design as followed: the participants are presented to a
stimuli, to which they have to answer, during which we recorded brain
activity using 64EEG cap system. On answer, a triggers is sent (S1 for
right, S2 for wrong). We therefore theoretically have 2 triggers per trial:
a stimulus onset trigger (S10, S20, S30 depending on condition) and an
answer trigger. The time between stimulus onset and answer varies, as
participant can answer within five seconds after stimulus onset. The issue
is that when importing the data in EEGlab, the response triggers get added
to the onset triggers. We therefore don't have any S1 or S2 triggers, but
only S12, S22... Moreover, some of the answer triggers disappear. We should
indeed have an answer trigger following each onset trigger, which is not
systematically the case. However, we processed the data using brain vision
analyzer, but the problem did not appear with this software (we still have
the S1 and S2 triggers, nor any missing triggers inbetween), despite using
exactly the same raw data. The problem seems to be due to the importation
of the data in EEGlab, as the problem is already present following
importation.
We could not figure out where the problem lies, and we are hoping you could
help us figure it out, as this could potentially impair our statistical
analysis.

Thanks in advance for your help,

Best

Alex Lepauvre
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