[FieldTrip] Help Manually Defining Trials

Pelt, S. van (Stan) stan.vanpelt at donders.ru.nl
Mon Jun 29 16:16:11 CEST 2015

Hi Peter,

In addition to Steve’s perfect suggestion, you might want to take a look at this example script, which basically is a data-driven way to define trials:


Here, co-recorded EMG-data is used to define trials, but in your case you can use (some parameter in) your MEG data (e.g., some ‘cleaniness’ measure).


Stan van Pelt, PhD
Donders Institute for Brain, Cognition and Behaviour
Radboud University
Montessorilaan 3, B.01.34
6525 HR Nijmegen, the Netherlands
tel: +31 24 3616288

From: fieldtrip-bounces at science.ru.nl [mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Stephen Politzer-Ahles
Sent: maandag 29 juni 2015 15:32
To: fieldtrip at science.ru.nl
Subject: Re: [FieldTrip] Help Manually Defining Trials

Hi Peter,

http://www.fieldtriptoolbox.org/reference/ft_definetrial describes the format of the trial definition matrix; you can simply create a matrix like this using the times that you would like to choose for your epochs, and then run ft_preprocessing() with this matrix as the input for cfg.trl. (This is basically a combination of methods (1) and (2) that you suggested below.)

Stephen Politzer-Ahles
New York University, Abu Dhabi
Neuroscience of Language Lab

On Mon, Jun 29, 2015 at 2:00 PM, <fieldtrip-request at science.ru.nl<mailto:fieldtrip-request at science.ru.nl>> wrote:

Message: 1
Date: Sun, 28 Jun 2015 23:51:19 -0400
From: Peter Lyons <plyons at udel.edu<mailto:plyons at udel.edu>>
To: FieldTrip discussion list <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>>
Subject: [FieldTrip] Help Manually Defining Trials
        <CALq-V2qi104MwTnq26qr4EwKPkZkBMEBzstS5JPRxZKVMrr=sw at mail.gmail.com<mailto:sw at mail.gmail.com>>
Content-Type: text/plain; charset="utf-8"

Dear All,

My name is Peter Lyons, and I am a researcher at the University of
Delaware.  Currently, I am conducting resting state EEG research with the
intention of using Fieldtrip to calculate the power of different frequency
bands as well as phase lag index between various sensors.  My dataset is a
continuous recording sampled at 1000 hz for 30 minutes.  I do not have any
events or triggers in my data.

I would like to manually select the cleanest segments of my data following
artifact rejection, and define them as trials.

Theoretically, I see three ways to segment my data manually:

1.  Insert individual triggers throughout my data (at locations determined
via ft_databrowser), and then define trials based on these triggers.

2.  Define trials based on a beginning and ending sample number.

3.  Use ft_databrowser to select segments of data as if they were
artifacts, and then define these "artifacts" as trials instead of rejecting
them from the dataset.

Could anyone advise on how to code one of the above methods?

Any help is welcome and appreciated!

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