[Eeglablist] biosig function and bio-semi triggers - mystery resolved?

[Baris Demiral]

Hi everyone,

I would like to comment on the previous discussion about the biogig import
of the bdf files, related to the warnings to some triggers. Some of you
previously reported that you see
the following error messages after importing bdf files with biosig function:
Warning SOPEN: number of event onset (TYP=0) and event offset (TYP=8000)
differ (371,366)
Warning SOPEN: number of event onset (TYP=5A) and event offset (TYP=805A)
differ (276,280)
Warning SOPEN: number of event onset (TYP=5B) and event offset (TYP=805B)
differ (85,88)

I recognized that this is due to the "response" triggers. Biosig
successfully detects triggers of Stimulus type (first 8 bits of the Status
channel) but it is not capable of
detecting the last 8 bits of the Status channel reserved for Response coming
mainly from the Switch-boxes.

That might be the reason why Arno and some other could not replicate this
bug, probably because they did not use Biosemi response switch (?). What
happens is that biosig somehow detects the Response trigger, but then it
marks them as "0s". I know that BioSemi marks the off-set of the response
switch (release) and puts "0".

Another reason for the warning might be that when you use response boxes, as
well as recording, say, accuracy by looking at the response, and send
triggers to eeg machine before the button release, they may add up and give
you weird trigger codes. But, the codes are not arbitrary and can be easily
converted.

Any comments? Anyone responsible for the Biosig function, could you reply
please?

Best,
Baris
-- 
SB Demiral, PhD.
Department of Psychology
7 George Square
The University of Edinburgh
Edinburgh, EH8 9JZ
UK
Phone: +44 (0131) 6503063
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