read_event for Neuromag 122 trigger events

Yang Zhang zhang470 at UMN.EDU
Fri Jan 8 21:00:45 CET 2010

Problem solved. I went through all the relevant files for the events in 4D
toolbox, MNE, and fieldtrip and realized that read_trigger.m must be revised
for my Neuromag-122 dataset. 

The threshold value 5 for fixneuromag as suggested by Joachim Gross for
read_trigger.m did not work for my data. I noticed that the default
threshold for detecting triggers was set at 0.1 in the MNE package, and the
threshold was set at 2 in Jensen's 4D toolbox for detecting the events in
the STI channels for Neuromag-122. In my dataset, the recorded amplitudes
for the triggers were about 4.98, and the noise floor in the STI channels
were smaller than 0.01. 

Because of the way the triggers were set up for Neuromag 122, the  section
for "switch detectflank" in read_trigger.m need to be bypassed. For a simple
solution, I just used Hamalainen's mne_make_combined_ event_file.m in
extracting the triggers and feed those parameters for event.type,
event.sample, and event.value. 


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