Averaging Across EEG Datasets from Different Recording Systems

The easiest way to create a grand average of files with differing electrode configurations is to use spatial interpolation to 81 standard positions. This will work for electrode nets with >81 electrodes (basically a spatial down-sampling), but it will also work for electrode nets with < 81 channels as BESA Research uses a spline interpolation that will calculate the signal at any position on the head surface based on the given information. Thus, it is possible to assume 81 standard electrodes distributed across the head and estimate their according signal. To use this spatial interpolation, do the following:

• In the Combine Conditions dialogue "ERP → Combine Conditions…" simply load all the individual average files you want to grand-average, no matter how many electrodes they contain
• In the second tab "Condition List" define your conditions as usual
• Leave the third tab "Channel List" untouched
• In the fourth tab "Run Script" the option "Interpolate to standard 81 electrodes" will be automatically checked. Make sure that the setting "combine data from source files" is also checked if you want to create a grand average.
• Press OK to start averaging.