## Appendix F Additional Graphs
### GA ERPs
#### Event-Related Spectral Perturbations, ERSP  
In Figures 11-11, the spectral perturbations are presented highlighted by bootstrapping at \(\alpha=0.01\) level, where no significant points are presented in green. For the top plots, the right color bar shows the scale of the power spectral density (\(-2.2\) dB); the lateral left panel shows the baseline mean power spectrum; the lower panel show the ERSP envelopes (low and high mean dB values, relative to baseline, at each time in the epoch, across all frequencies). Bottom plots show the Inter-Trial Coherence (ITC), where the right color bar shows the coherence strength scale (ITC values); the left panel shows the ITC frequency mean (blue trace) and ITC significance limits at each frequency (green trace); and the panel underneath shows the mean ERP trace.  
**Uni perception** (Figure 11): The ERSP in the left parietal side (P3) show desynchronizations in the early interval (0-200 ms), and also later after 600 ms for up to 22 Hz and weaker beyond 22 Hz. The ITC measure ranges from zero to one for a specific time-point, explicitly from no synchronization between the EEG epochs to strong synchronization. For a given frequency range, it provides the magnitude and phase of the spectral estimation. It shows here that trials are phase-locked at 850 ms for up to 20 Hz, corresponding to the second group of P200-P300 peaks, a time-locked response relating effectively to visual processing for the grey image presentation event.  
**Nat perception** (Figure A5): The desynchronizations are stronger and extended in frequency and time, more pronounced in the \(\gamma\) frequency (over 30 Hz) for the T4 channel as compared to Uni image perception. For parietal site, lower ERDs are observed after 600 ms including also \(\gamma\) band. Considering ITC, no phase synchronization between trials is observed for the first group of P200-P300 peaks, since it includes the thought process of perception which is different between image to image.  
**Frac perception** (Figure A6): For fractal perception, the strong desynchronizations continue until 30 Hz for P3, after 600 ms, and until 20 Hz for T4 after 600 ms. Synchronization is also observed for T4 at 250-450 ms in the \(\beta\) band (20-30 Hz), effect significant as detected by bootstrap statistics at 0.01 confidence level.  
Comparing between Uni, Nat and Frac images perceptions, the effects tend to suggest a more complex cognitive process for Nat perception, with extended ERDs in higher bands and not significant for Frac perception in the parietal sites. While significant and extended ERDs in \(\beta\) and \(\gamma\) observed for Nat perception in the temporal area, with only in \(\gamma\) (>30 Hz) for Frac perception, tend to indicate higher memory recall activity for Nat and intensive for Frac images. The representative perturbations in the \(\alpha\) frequency band relate to attention and an easier processing, while in addition, the significant beta and gamma modulations represent more complex mental activity [87]. The strong synchronization within the baseline period (\(-400\), \(-200\)) ms relates to a time-locked visual response to the attentional image, process identical in all three cases.