The process of close-reading and cross-referencing the EEG data with the tracked gaze positions is very time consuming. However, by using Matlab its EEG plugin, I could analyse the raw data much more efficiently. The EEGlab plugin lets the user run Fourier and Event-Related Spectral Perturbation (ERSP) analyses.
As we know EEG data consist of a mix of complex frequencies that change rapidly over a short period of time. A Fourier transform is broadly used in the study of harmonics, and basically decomposes complex frequencies and in this case represents the function of frequency domains and the sum of their amplitude. The figure below shows a simplified Fourier transfer. On the left we see a “complex” signal mixture of 2Hz, 10Hz, and 20Hz frequencies. On the right, after the Fourier transfer we see three peaks with the same amplitude at 2, 10, and 20Hz.
The ERSP analysis is used to study event related brain dynamics. This method adds a third dimension of time to the analysis. This way we can get a better understanding when peaks of certain EEG frequency bands (aplha, beta, gamma) occur. The figure below is from auditory evoked response experiments during a four day study of the effects of 24-hour free-field exposure to intermittent trains of 89 dB low frequency tones (sccn.ucsd.edu)