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

EEP 3.1 - MPI/ANT(eeprobe@ant-software.nl), 05.08.1999
Copyright © 1996-99 Max-Planck-Institute of Cognitive Neuroscience. All rights reserved.