Trigger Files
Contents
Introduction
EEP uses trigger files - simple ASCII lists of time/code pairs - to mark
certain time points in the continuous EEG records. These are used
by different EEP modules to navigate on the time axis, especially to find
and classify the interesting trial epochs.
This concept allows to control the evaluation by editing the table. Since
there is a lot of great software for all kind of text manipulation available,
we have infinite flexibility and power here at no cost.
Specification
The trigger ASCII list consists of one header line followed by one
line for each trigger
<interval> <blocksize>
<time_1> <offset_1> <code_1>
<time_2> <offset_2> <code_2>
...
<time_n> <offset_n> <code_n>
where the components are:
- interval
- Sampling interval (in seconds). This is
normally compared with the interval stored in the cnt file to detect
mismatches.
- blocksize
- Size (in bytes) of the data block for one sample in the EEP 2.0
fileformat
(Nchannels * 2 + 4).
This value is unused in EEP 3.x
programs but the parser expects to find a number here.
- time
- Trigger position (in seconds).
- offset
- File offset (in bytes) in the EEP 2.0 fileformat which corresponds
to the trigger position
(900 + (blocksize - 4)/2 * 75 + time/interval * blocksize).
This value is unused in EEP 3.x
programs but the parser expects to find a number here.
- code
- String of max. 8 letters, digits, underscores. Note
that case-insensitive string comparisons are performed to find triggers -
"1", "01", "001" are all different values, "foo", "Foo" and "FoO" are
equal values.
Example
0.00400000 52
4.236 57768 11
4.328 58964 12
4.740 64320 13
4.996 67648 14
8.904 118452 91
12.732 168216 31
12.828 169464 32
13.172 173936 33