[Eeglablist] comparing conditions

Ahmad, Jumana jumana.ahmad at kcl.ac.uk
Thu Jan 19 01:43:35 PST 2017

Thank you very much for your useful notes.

I read of Makoto’s pre-processing pipeline that:

‘When creating STUDY with epoched data (assuming that you have within-subject conditions), I recommend that you use one set file per subject and never save the data separately for each condition (which is an old approach used before STUDY.design was implemented). In theory both works, but there were reports of problems caused by separate .set files. I recommend you use STUDY.design to let STUDY know the factorial design of the analysis.’

Also, I read on the EEGlab documentation:
The main advantages of using STUDY designs are detailed below:
No need to have one dataset per condition. An important restriction of working with STUDY structures in EEGLAB 8.0 (prior to STUDY.design) was that to compare multiple conditions users had to generate one dataset per condition. However, to analyze the influence of various contextual information about trials, it may be relatively impractical to generate many datasets with specific sets of trials. The new 'design' scheme in EEGLAB 9.0 is backward compatible with EEGLAB 8 but allows for more flexibility, in particular allowing the STUDY functions to dynamically extract specified data trials from datasets. Each dataset may contain several conditions or several datasets can be merged, using the STUDY design facility, to form to one condition.

Therefore, I would be interested to have one set file for all my conditions, but the tutorials I find online use different .set files per condition.

Do I just do everything the same as the tutorials but per condition, keep loading the same file?

Best wishes,


From: Tarik S Bel-Bahar [mailto:tarikbelbahar at gmail.com]
Sent: 17 January 2017 22:30
To: Ahmad, Jumana <jumana.ahmad at kcl.ac.uk>
Cc: eeglablist at sccn.ucsd.edu
Subject: Re: [Eeglablist] comparing conditions

Hello Jumana, brief notes below, best wishes!

To make the STUDY machinery work, it's necessary to make separate files for each of your different conditions and subjects.
I believe that this is the way the current STUDY works, unless there's been major updates (see current revision lists for eeglab)

If you wanted to do it by loading one file, you would have to do it with coding new matlab code to
feed information to the STUDY functions, essentially using eeglab to create the 4 condition files inside matlab memory in the format of ALLEEG structure. This would take a bit of time, as you would have to really understand the code of the STUDY functions very well. It would be better to make use of the study functions initially, learn how they work, and then if you have time build your own version.

If you're interested in other options, you should review the data structures in Fieldtrip and other eeg analyses programs.
You may also benefit from reading Mike Cohen's books on Time-Frequency analyses, which has a nice discussion of
building a data hypercube (of metrics X subjects X conditions) of spectrogram or other data,
which you can interogate as you wish, and then apply functions from eeglab or other programs.

If you are still new to matlab coding and digging into functions, which require a moderate level of expertise, and you still want to build your own method, it is recommended you make contact with a researchers that have larger labs that use eeglab, and consulting with one of the students or scientists there. You might also find a consultant on the eeglab list.

On Tue, Jan 17, 2017 at 4:59 AM, Ahmad, Jumana <jumana.ahmad at kcl.ac.uk<mailto:jumana.ahmad at kcl.ac.uk>> wrote:
Dear EEGlab,
It says on the website that to compare event-related EEG dynamics for a subject in two or more conditions from the same experiment, it is first necessary to create datasets containing epochs for each condition. Is this still the case or can I keep all my conditions in one file?
Is the same true for study? If I can keep one file, please can you advice me on how I can load the data using one file? The tutorial shows loading separate files per condition. I would happily use code to do this.
Best wishes,

Jumana Ahmad
Post-Doctoral Research Worker in Cognitive Neuroscience
EU-AIMS Longitudinal European Autism Project (LEAP) & SynaG Study
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