[FieldTrip] Biosemi eventtype problem

[Ricarda Braukmann]

Hi Vitoria,

I had a problem with biosemi markers not being read in correctly by FT as
well.

First of all, if I remember correctly, using ft_read_event only worked for
me with .bdf files (and not .edf files).
Still even with the .bdf files, the numbers were not correct.
This was caused by the fact that the biosemi system always sent out two
markers to the EEG (one constant marker and one marker specific to stimulus
presentation).
FT for some reason did not recognize these markers as 2 (8bit) markers but
created 1 16 bit marker from it.

Once I knew this it was easily solved, I just recoded the markers.
Not sure whether this is what is happening with your set-up as well (might
be different with newer ft versions), but maybe it helps.

In any case, I belief that the biosemi STATUS markers are indeed not
strings.

Best,
Ricarda

On Wednesday, January 21, 2015, Alexander Maye <a.maye at uke.de> wrote:

> Hi Vitoria,
>
> with this minimal description it's hard to say what the problem is, but
> these
> are the things that come to my mind:
> - Did you setup/modify a config file for the ftbuffer, and did you start
> the
> buffer with this config?
> - Sometimes the higher bits of the parallel port are set, giving you event
> values >60.000. Maybe you could mask out the bits that you are interested
> in?
> Another possibility is that ftbuffer's event values are in two's-complement
> format. In any case you could check the output of the ftbuffer program - if
> your events aren't there, your program will not see them either.
> - Transition from some value to zero are not detected as events as it
> seems.
>
> Hope this helps,
>
>                 ALEX.
>
>
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