# Color Texture Image Complexity--EEG-Sensed Human Brain Perception vs. Computed Measures
## 7 Experimental Results
### EEG Experiment Analysis
#### 7.3.1 Natural Images  
ERPs vs. CE  
First, it is important to note the CE complexity levels distributions among images: low: 34% of images; medium: 34%; and, high: 32%, which are balanced between classes, so we can rely on Grand Average ERPs interpretation, since unbalanced classes could influence the mean in favor of the class with more trials. The Grand Average (GA) amplitudes of the ERPs at channel P4, as shown in top plot in Figure 6, is gradually increasing once with an increased level of complexity, as expressed by CE. The scalp maps likewise show increased activity in the parietal area (P3, P4 channels) for the P200 peak (300-400 ms), P300 peak (400-500 ms), and second P3b (1200-1300 ms). We observe that, for a lower level of complexity (low, medium), the neural activity focuses also in the visual area probably relating to more aspects of attention and visualisation [71; 72], while, for a complex level, only the parietal area is activated involving a more complex decision and it is right lateralized, tending to suggest imagery processes [73; 74; 75; 76]. However, no significant correlation was detected here in relation to CE levels, which might probably be due to few high correlations between participants answers and computed measures, as seen in Table 3. In addition, the ERP amplitude varies from trial-to-trial due to many factors, and a direct proportional connection to the increase in CE values is therefore hard to detect. ERPs vs. CFD  
The CFD complexity levels distributions: low: 33%; medium: 35%; high: 32% (balanced). The ERP responses in time for _Nat_ images according to the CFD levels as shown in Figure 7 indicate a gradual increase in amplitude, proportional with a higher level of complexity (low CFD complexity--blue; medium--red; high--orange), visible also over all channels (Figure A1 in Appendix A); however, only N300 at the P4 channel correlate significantly (\(\rho=0.23\)) with the CFD values considering the trial averages across participants. The gradual increase in amplitude and spatial activity can be seen in Figure 7, with more parietal activity as with a complex level and less frontal activity (only visible for P3 peak at 400-500 ms). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **P1** & **P2** & **P3** & **P4** & **P5** & **P6** & **P7** & **P8** & **GA** \\ \hline CE–N3 & \(\mathbf{-0.25}\) **(P3)** & & & \(\mathbf{0.34}\) **(P3)** & & & & \\  & & & \(\mathbf{0.29}\) **(P4)** & & & & & \\ \hline CE–P3 & \(\mathbf{-0.21}\) **(P3)** & & & & & & \\  & \(\mathbf{-0.26}\) **(P4)** & & & & & & \\ \hline CE–P3b & \(\mathbf{-0.25}\) **(P3)** & & & \(\mathbf{0.25}\) **(P3)** & & & & \\  & \(\mathbf{-0.27}\) **(P4)** & & & & & & \\ \hline CFD–N3 & & & \(\mathbf{0.34}\) **(P3)** & & & & & \\  & & \(\mathbf{0.26}\) **(P4)** & & & & & \\ \hline CFD–P3 & & & & & & & \(\mathbf{0.21}\) **(P3)** & **0.22** **(P3)** \\ \hline CFD–P3b & & & \(\mathbf{0.27}\) **(P3)** & & & & \(\mathbf{0.26}\) **(P4)** & **0.22** **(P3)** \\ \hline sbj–N3 & & & \(\mathbf{-0.26}\) **(P3)** & & & & \\ \hline sbj–P3 & & & \(\mathbf{-0.22}\) **(P3)** & & & & \\ \hline sbj–P3b & & & \(\mathbf{-0.24}\) **(P3)** & & \(\mathbf{-0.21}\) **(P3)** & & \(\mathbf{0.22}\) **(P4)** \\ \hline CE–\(\alpha\) & & & & & & \(\mathbf{-0.23}\) **(P3)** & \\ \hline CE–\(\beta\) & & & & & & \(\mathbf{-0.24}\) **(P3)** & \\ \hline CFD–\(\alpha\) & \(\mathbf{-0.24}\) **(P3)** & & \(\mathbf{-0.23}\) **(T4)** & \(\mathbf{-0.21}\) **(T4)** & & & \\ \hline CFD–\(\beta\) & & \(\mathbf{0.21}\) **(T4)** & & \(\mathbf{-0.25}\) **(T4)** & \(\mathbf{-0.2}\) **(P4)** & & \\ \hline \hline \end{tabular}
\begin{tabular}{c} sbj–subjective evaluation scoring. \\ \end{tabular}
\end{table} 
Table 5: Neural signals versus CE and CFD correlations for _Nat_ and _Frac_ images. The result values on _Frac_ textures are shown in bold and normal font for _Nat_. The respective channel is indicated in brackets. ERPs vs.