Naming and Organising Data Files

Introduction:

When you write a script to analyse your data, you'll need to tell MATLAB which files you want to open and where they are. You can make your life and code a lot simpler, If you:

1. name your files consistently, and

2. have an organised folder structure for storing your files

Step 1. Make sure your data files have good file names:

In my opinion, a good file name (1) contains sufficient identifying information about the dataset and (2) expresses this in a consistent way. What you should include exactly, depends on the complexity of your study.

• In the most simplest form (let's say you had a single-group design), the file name could contain just the Participant ID code (e.g. P001ML29).

  • My formula for creating Participant ID codes is: Participant Number + Gender + Dominant Hand + Age

    • 'P001ML29' - stands for participant number 1, Male, Left-Hand Dominant, 29 years old.

    • Start with a letter - 'P001FR09' and not '001FR09' - I think EEGLAB doesn't like file names that start with numbers.

    • Have the same length- 'P003FR09' and 'P010MR25' are the same length, but 'P3FR9' and 'P10MR25' are not.

• You could also put the study name to avoid getting mixed up between studies (e.g. P001ML29_forceP3) - but I don't because it makes your file names long and it's not necessary if you're data is stored carefully.

• If your study design is more complex, for example, if each participant does multiple sessions, or you have a separate group design, additional identifying information should be included in the file name, separated by underscores. The file extension should be unchanged.

  • For Multi-session: Participant ID + Session = e.g. P001ML29_S1, P001ML29_S2

  • For Multi-group: Participant ID + Group/Condition = e.g. P001ML29_contr, P002MR30_treat

    • Make sure the group/condition label has the same number of characters (contr and treat are both 5 characters long)

  • For Multi-session + group: Participant ID + Session + Group/Condition = e.g. P001ML29_S1_contr, P001ML29_S2_treat

• Other rules for consistency:

  • Use consistent spelling for each groups/condition - if you want 'contr' to represent the control condition, make sure you use that throughout. It doesn't matter what you use, just do it consistently.

  • Capitalise consistently

  • Only use letters, numbers, and underscores - avoid other characters, especially spaces.

Step 2. Create and Organise your Project Folder:

• Create a Project Folder - Create a new folder for your project and give it a name (e.g. P300_force_study)

• Create Sub-folders - Inside of your project folder, create some more folders for your data, code, plots, manuscripts, and other documents.

This is how I organise my project folder. Feel free to create more folders if you have a group of files that don't fit in nicely to any of these folders, or delete folders that are not relevant to you.

• Project_folder

  • data

    • raw_eeg - store raw EEG data and nothing else

    • processed_eeg - store processed EEG data - the output of the pre-processing MATLAB script

    • behavioural_data - store behavioural data - I have an excel sheet that contains trial-by -trial data for each participant for trial-type, RT, accuracy etc.

    • exported_data - stores any summarised outputs from the processing script which are ready for statistical analysis

  • code

    • experiment_code - store code used to run the actual experiment, with stimuli files

    • analysis_code - store MATLAB and R code for pre-processing and statistical analyses

  • plots

    • individual - stores individual waveform and scalp map plots - if you choose to do this- I find this is a quick way to identify problematic data

    • grand-average - stores waveform and scalp map plots averaged across all participants - useful for giving an overview of the data

  • manuscript

    • figures - to store task diagrams and finalised result plots

    • submission - to store submitted versions of the manuscript, cover letters, separated abstract and highlights

      • • revision - to store revised manuscript, and response letter to the editor and reviewers

  • other_documents - storing files like consent forms and information sheets

Step 3: Put files in the appropriate locations

• Put the raw EEG data files in the data > raw_eeg folder

  • Don't put anything else in this folder - this way you can tell MATLAB to loop through all the files in this folder.

Ok, now we are ready to start writing some code!