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

[Alois Schloegl]

Some time ago, based on user feedback, I've already set the default 
decoding method in biosig/t200/bdf2biosig_events.m also to
    case 4 (rising edge, of lower 15 bits)
Also for Baris, this mode is working fine.

Therefore, I suggest that the default decoding method in eeglab should 
be also changed to this method, and as used in biosig.


Kind regards,
    Alois Schloegl




On 04/20/11 13:26, Baris Demiral wrote:
> 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
>
>
>
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