[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


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



Paul F Sowman
Associate Professor
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Department of Cognitive Science
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Subject: fieldtrip Digest, Vol 107, Issue 14

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Today's Topics:

1. Difficulty detecting TTL pulses with ft_read_event
(Jonathon James Parker)


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
<BYAPR02MB5750759FB50F1B32AD4033ABAD650 at BYAPR02MB5750.namprd02.prod.outlook.com>

Content-Type: text/plain; charset="windows-1252"

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 J. Parker MD PhD
Stanford University
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