[FieldTrip] Difficulty detecting TTL pulses with ft_read_event
Paul Sowman
paul.sowman at mq.edu.au
Tue Oct 29 02:29:41 CET 2019
Hi Jonathon, you could try something like this:
trigger_nums = 161:225; %TTL channels
triggers = ft_read_data(cfg.dataset,'dataformat','yokogawa_con','chanindx',trigger_nums); %read in data from MEG
hdr = ft_read_header(cfg.dataset,'dataformat','yokogawa_con');
for j=1:size(triggers,1)
trig_height(j) = max(triggers(j,:)); %find the peak voltage in trigger channel
end
trig_thresh = 0.25*max(trig_height); % threshold 1/4 of trigger max
triggers = triggers>trig_thresh; %Binarise trigger channels
event = [];
list = trigger_nums;
for k=1:size(triggers,1)
channel = list(k);
trig = triggers(k,:);
pad = trig(1);
trigshift = 0;
begsample = 1;
for l=find(diff([pad trig(:)'])>0)
event(end+1).type = num2str(channel);
event(end ).sample = l + begsample - 1; % assign the sample at which the trigger has gone down
event(end ).value = trig(l+trigshift); % assign the trigger value just _after_ going up
end
end
--
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Today's Topics:
1. Difficulty detecting TTL pulses with ft_read_event
(Jonathon James Parker)
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Message: 1
Date: Fri, 25 Oct 2019 17:56:22 +0000
From: Jonathon James Parker <parkerjo at stanford.edu>
To: " fieldtrip at science.ru.nl" <fieldtrip at science.ru.nl>
Subject: [FieldTrip] Difficulty detecting TTL pulses with
ft_read_event
Message-ID:
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Hi FieldTrippers:
I am a LFP/Brain stimulation researcher new to FieldTrip @Stanford.
I have run across some difficulty using the ft_read_event to detect TTL pulses and triggering my data into discrete epochs
I have 14 channels of LFP data and 1 channel of trigger data recording using a gTec USBAmp-Research. I have successfully read in the data, filtered-it, re-referenced channels of interest, and appended the un-filitered trigger channel (‘TRAIN’).
The TTL pulses are on (value ~1) while stimulation is on. I would like to trigger based on the upgoing flank.
Each time I run ft_read_event, I have passed it the isolated trigger channel data, but I receive this error:
[cid:image002.png at 01D58B22.76EEAD40]
Does anyone have sample scripts they could share with use of ft_read_event to detect TTL pulses?
See my full code below:
[cid:image004.png at 01D58B22.D7510DE0]
Thank you!
Jonathon
Jonathon J. Parker MD PhD
Stanford University
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