Complex Demodulation

Time-frequency transforms are obtained in a very fast implementation based on complex demodulation. Apart from source channels,

intracranial channels, and scalp channels, also other polygraphic channels, e.g. rectified EMG, can be included into the analysis.

The principal steps to calculate a time-frequency diagram and source coherence are illustrated in the figure below for the real

data example of error-related negativity (ERN). A multiple source model is created from averaged ERP data and/or sources in

brain regions known to contribute from fMRI/PET studies using a similar task. The source model is then used to calculate a source

montage and the source waveforms of the single trials. Next, each single trial is transformed into the time-frequency domain by

selecting a certain temporal resolution using complex demodulation (a principle similar to FM radio).