3.2: Exercise- Preprocessing and Averaging the Data from 10 Participants
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Before you start this exercise, quit from EEGLAB if it’s already running and then restart it so that you’re starting fresh. You might even want to restart Matlab. Set Chapter_3 (the folder with the data you downloaded for this chapter) to be Matlab’s current folder.
For this chapter, you’ll need averaged ERPs from 10 participants. You have three options for obtaining these ERPsets:
You can go through all the steps from Chapter 2 for each participant using the EEGLAB/ERPLAB GUI. The Chapter_3 folder contains a folder for each participant containing the raw EEG data, just like the data you processed in Chapter 2. This will take quite a bit of time, but you’ll really learn the preprocessing steps well by repeating them for each participant.
You can run the script named preprocess_and_average.m (which is in the Chapter_3 folder). It will run all the processing steps automatically and create the ERPset for each participant. The script file contains instructions for running it. The advantage of this approach is that you’ll get more comfortable running Matlab scripts (which will become increasingly useful as you progress through the book). If you’d like, you can process some or all of the participants manually first and then run this script. When you’re processing your own data, this is the right approach: You first process the data manually to make sure everything is OK, and then you run a script to reprocess the data to avoid any errors in the manual processing.
There is a subfolder named Pre-made_ERPsets inside the Chapter_3 folder that contains—you guessed it!—a pre-made ERPset for each participant. You can just move those ERPsets into the single-participant folders inside the Chapter_3 folder. This is the quick-and-easy approach, but you won’t learn as much.
No matter which way you do it, make sure that you end up with an ERPset file named N _N400.erp inside folder N for each participant (where N is the participant number). Then, load all 10 of these ERPsets into EEGLAB/ERPLAB (either with the script or using EEGLAB > ERPLAB > Load existing ERPset ). The ERPsets menu should now look like Screenshot 3.1.