Chapter 04: STUDY Data Visualization Tools
Description of experiment for this part of the tutorial: These data were acquired by Arnaud Delorme and colleagues from fourteen subjects. Subjects were presented with pictures that either contained or did not contain animal image. Subjects respond with a button press whenever the picture presented contained an animal. These data are available for download here (380 Mb). A complete description of the task, the raw data (4Gb), and some Matlab files to process it, are all available here.
We have used these data in the following two sections since the released cluster tutorial data used in previous sections are too sparse to allow computing statistical significance. However, for initial training, you might better use that much smaller example STUDY.
Precomputing channel measures
Before plotting the component distance measures, you must precompute them using the Study > Precompute measures menu item as shown below.
It is highly recommended that for visualizing and computing statistics on data channels you first interpolate missing channels. Automated interpolation in EEGLAB is based on channel names. If datasets have different channel locations (for instance if the locations of the channels were scanned), you must interpolate missing channels for each dataset from the command line using eeg_interp.m. Select all the measures above, or just one if you want to experiment. The channel ERPs have been included in the tutorial dataset; if you select ERPs, they will not be recomputed -- unless you also check the box Recompute even if present on disk.
Each measure to precompute is explained in detail in the component clustering part (where the same exact measures may be computed).
Plotting channel measures
After precomputing the channel measures, you may now plot them, using menu item Study > Plot channel measures.
Here we only illustrate the behavior of pop_chanplot.m for plotting ERPs. Spectral and time/frequency (ERSP/ITC) measure data for scalp channels may be plotted in a similar manner, as shown in the previous section on component clustering. To plot data for a single scalp channel ERP, press the Plot ERPs pushbutton on the left column. A plot like the one below should appear:
You may plot all subjects ERPs by pressing the Plot ERPs pushbutton in the left columns, obtaining a figure similar to the one below.
Finally, you may also plot all scalp channels simultaneously. To do this, simply click the push button Sel. all to select all data channels. Then again press the Plot ERPs button in the right column.
Clicking on individual ERPs will make a window plotting the selected channel ERP pop up. Many other plotting options are available in the central column of the pop_chanplot.m gui. These will be described in the next section.
More complex plotting options are demonstrated in the section dealing with visualization and statistics.