Organize your EEGLAB datasets to STUDY

Creating a STUDY

This part of the tutorial will demonstrate how to create an EEGLAB STUDY and perform simple plotting. An EEGLAB STUDY (or study) contains descriptions of and links to data contained in many epoched or continuous datasets, for example, a set of datasets from a group of subjects in one or more conditions of the same task or performing different tasks in the same or different sessions. We use a STUDY to manage and process data recorded from multiple subjects, sessions, and/or conditions of an experimental study.

Creating a new STUDY

To create a STUDY, select the File → Create study → Browse for datasets menu item.

Another option is to load into EEGLAB all the datasets you want to include in the study and select the File → Create study → Using all loaded datasets menu item. A blank interface similar to the one described below will appear. In this window, enter a name for the STUDY (‘N400’), and a short description of the study (‘Auditory task: Synonyms Vs. Non-synonyms, N400’).

Here, we do not add notes about the study, but we recommend that you do so for your own studies. The accumulated notes will always be loaded with the study, easing later analyses, and re-analyses. Note that here the fields Subject and Condition (above) have been filled automatically. This is because the datasets already contained this information. For instance, if you were to load this dataset into EEGLAB by selecting the Edit → Dataset info menu item, you would be able to edit the subject, condition, group, session, and run for this dataset. You may also edit this information within the study itself. The dataset information and study dataset information may be different to ensure maximum flexibility, although we recommend checking the checkbox Update dataset info… to keep them consistent.

Click on the Browse button in the first blank location and select a dataset name. Do so for other datasets as well.

The interface window should then look like the following:

Below, we detail what the STUDY terms subject, session, run, condition, and group mean.

  • The top of the window contains information about the STUDY, namely its running name, the extended task name for the STUDY, and some notes.

  • The next section contains information about the 10 datasets that are part of the STUDY. For each dataset, we have specified a subject code and condition name.

  • For each file, you may assign a session and run number. A run is when there are blocks in an experiment, and the data from each block is stored in a separate file. Sessions are used when the data is collected on different days or when there is a break that involves removing the EEG cap. We chose to leave the session and run empty since there are irrelevant for this STUDY (there is only one session and one run per subject).

  • The condition column contains the condition associated with each file. Note that we have two files here per subject. However, it is also possible to have a single file per subject and to define conditions using EEGLAB event trial types. For more information on this topic, read the STUDY design tutorial.

  • The group column indicates the group a subject belongs to. This is irrelevant for this STUDY since there was only one subject group.

  • We will come back later to the Select by r.v. (select ICA component by residual variance) and the Comp… button when we perform ICA component clustering.

  • Pressing the Clear button clears the information on a given row.

In general, we prefer the dataset information to be consistent with the STUDY information – thus, we may check the first checkbox. The second checkbox removes all current cluster information and will be explained when we perform ICA component clustering.

After you have finished adding datasets to the study, press Ok in the pop_study.m GUI to import all the datasets.

We strongly recommend that you also save the STUDY by selecting the EEGLAB menu item File → Save study as after closing the pop_study.m window.

Loading an existing STUDY

Either use the studyset created in the previous section or load another studyset. To load a studyset, select the File → Load existing study menu item. Select the file N400.study in the folder STUDY5subjects. After loading or creating a study, the main EEGLAB interface should look like this:

Study Window

In the EEGLAB GUI (above):

  • Epoch consistency indicates whether or not the data epochs in all the datasets have the same lengths and limits.

  • Channels per frame indicates the number of channels in each of the datasets (It is possible to process datasets with different numbers of channels).

  • Channel location indicates whether or not channel locations are present for all datasets.

  • Clusters indicates the number of component clusters associated with this STUDY. There is always at least one cluster associated with a STUDY. This contains all the pre-selected ICA components from all datasets.

  • Status indicates the current status of the STUDY. In the case above, this line indicates that the STUDY is ready for pre-clustering.

To list the datasets in the STUDY, use the Study → Edit study info menu item. The interface described in the previous section will pop up.

Editing STUDY datasets

Selecting an individual dataset from the Datasets menu item allows editing individual datasets in a STUDY.

Note, however, that creating new datasets or removing datasets will also remove the STUDY from memory since the study must remain consistent with datasets loaded in memory (EEGLAB will prompt you to save the STUDY before it is deleted).