Matlab - Load NEDF and EASY Files using the NE EEGLAB Plugin

Description

This article covers how to correctly load .nedf and .easy recordings using the Neuroelectrics EEGLAB plugin: installing the plugin, choosing the right loading function, and the channel-selection syntax that most often trips people up.

Materials / Devices / Software

• MATLAB

• EEGLAB

• NE EEGLAB Plugin (EEGLab-Plugin-master)

• .nedf or .easy recording file

Pre-requisites

• EEGLAB installed

• NE EEGLAB Plugin (EEGLab-Plugin-master) downloaded

Step-by-step guide

1. Install the plugin

Place the plugin folder inside EEGLAB's plugins directory.

<your_eeglab_folder>/plugins/EEGLab-Plugin-master/

• The xml4mat folder must stay inside EEGLab-Plugin-master, not in the main EEGLAB directory.

• NEDF files will fail to load if xml4mat is moved out of that folder.

2. Load a NEDF file

Use pop_nedf.m to load the recording.

pop_nedf('recording.nedf', 1, 0, '32');

• Argument 1 — file: path to the .nedf file.

• Argument 2 — acc: 0 or 1, whether to load accelerometer channel data.

• Argument 3 — locs: 0 or 1, whether to load channel location data.

• Argument 4 — channels_selected: channel indices as a quoted string, e.g. '32' or '1,2,5'; an empty string '' loads all channels.

3. Load an EASY file

Use pop_easy.m to load the recording.

EEG = pop_easy('recording.easy', 0, 0, '32');

• Arguments follow the same order as pop_nedf: file, acc, locs, channels_selected.

• channels_selected must be a quoted string here too, e.g. '32' or '1,2,5'; an empty string '' loads all channels.

4. Confirm the load succeeded

Check that the function returned without error and that data is now available.

• An EEG struct (or equivalent data variable) should appear in your MATLAB workspace or the EEGLAB GUI.

• Data is recorded in nV; the plugin converts it to µV automatically on load.

• .easy files are plain-text but are fully decoded — they do not carry lower amplitude precision than .nedf.

Common Problems

Load fails with a channel-selection / str2num-related error

• The channel-selection argument (4th parameter to pop_nedf or pop_easy) must be passed as a quoted string, even for a single channel — it's parsed with str2num, which requires string input.

Correct:   '32'

Incorrect: 32

"Undefined function 'eeg_checkset' for input arguments of type 'struct'"

• EEGLAB is not installed, or not initialized in the current MATLAB session, since pop_easy.m and pop_nedf.m both depend on core EEGLAB functions like eeg_checkset.m. Run this once per MATLAB session before calling pop_easy or pop_nedf:

eeglab;

close;   % optional, closes the GUI window