Visual paradigm and statistics. A, Example of eye-tracking data of free-viewing exploration of a natural scene. Each dot represents a gaze sample (at 500 Hz). Saccade and fixation samples are black and red, respectively. Fixation durations (in milliseconds) are displayed adjacent to each fixation. B, Eye tracker (ETH, horizontal channel; ETV, vertical channel) and raw EEG data [here EOG horizontal (EOGH), EOG vertical (EOGV), O1, and O2 channels] for the trial represented in A. Eye tracker data were used to identify saccade (red dashed vertical lines) and fixation onsets (gray vertical lines). Data were segmented in 2 s epochs centered on fixation onsets, with possible overlap, as shown by light blue boxes. C, Distribution of fixation durations. D, Distribution of saccade amplitudes. E, Angle histogram of saccade directions. F, Left, Average horizontal EOG of all rightward saccades (direction between −30 and 30°) before (black) and after (red) removing ocular movement ICA components. Right, Same signals for the EOGV channel and upward saccades (direction between 60 and 120°). G, Averages as in F, for occipital channels (O1 and O2) for rightward (left) and upward saccades (right). H, Left, Example of processing of raw EEG data. After epoch extraction and rejection of ocular artifacts through ICA analysis (data not shown), every epoch was convolved with a complex wavelet, producing information about phase at different times. Instantaneous phase at time 0 (fixation onset) was subsequently used for sorting, for grouping data epochs, and to generate data of the three models. Right, fERP and model predictions of an EEG data epoch for the first 200 ms after fixation onset (black lines). In the ongoing-activity model (ONG), an oscillation at the frequency of interest was generated with instantaneous phase φ₁ at 0 ms (blue). In the phase-resetting model (RES), the first 57 ms correspond to an ongoing activity signal (blue line) generated in the same way as with ONG. After 58 ms, however, a resetting component (red) starts, with a fixed phase of −π/2. The superposition model (SUP) comprises the addition of a continuous ongoing component (blue) and a resetting component (red) starting at 57 ms. I, Left, The same procedure as in H was used here to determinate instantaneous phase at the previous fixation onset (φ_1prev). With this information, predictions of phase shifts between fixations were generated by the three models. Right, For ONG, θ_adv is the phase after Δt ms of an oscillation at the frequency of interest that starts with phase φ_1prev. For RES, θ_adv is the phase after (Δt − 57) ms of an oscillation at the frequency of interest that starts with fixed phase −π/2. In SUP, θ_adv is the phase after Δt ms of the oscillation resulting from the addition of an ongoing and reset component (as in H, SUP).