# Machine Learning Based Color Classification by Means of Visually Evoked Potentials
## 4 Discussion
### Study Design and Measurement Setup  
The colors were chosen to be red and green in order to be classified in this study. From theoretical considerations, it was assumed that these two complementary colors could show a large difference in the range of VEPs. However, other color combinations may even perform better in terms of color classification, while red and green have the lowest discrimination threshold for this specific type of color classification. Additionally, it is not clear whether the observed differences are caused by the two colors or by (subjectively felt) intensity differences. Although the light density of the two colors was adjusted to have the same value; that is \(15\ \mathrm{cd/m^{2}}\), the subjective sensation of the test subjects may have differed for the two colors. Interestingly, the subjects described the green/black checkerboard to be brighter than the red/black one. In this context, further investigations could be carried out, dealing with different intensities and colors.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**Individual Participant**} \\  & **Accuracy** & **AUC** & **F1-Score** \\ \hline S1 & \(0.9938\pm 0.0198\) & \(0.9944\pm 0.0176\) & \(0.9941\pm 0.0186\) \\ S2 & \(0.8625\pm 0.0922\) & \(0.8814\pm 0.0829\) & \(0.8637\pm 0.0852\) \\ S3 & \(0.7375\pm 0.1277\) & \(0.7564\pm 0.1365\) & \(0.7281\pm 0.01552\) \\ S4 & \(0.9125\pm 0.0734\) & \(0.9244\pm 0.0664\) & \(0.9098\pm 0.0825\) \\ S5 & \(0.7500\pm 0.0722\) & \(0.7660\pm 0.0744\) & \(0.7448\pm 0.0872\) \\ S6 & \(0.7438\pm 0.01081\) & \(0.7540\pm 0.1088\) & \(0.7445\pm 0.1143\) \\ S7 & \(0.9250\pm 0.0655\) & \(0.9351\pm 0.0581\) & \(0.9274\pm 0.0623\) \\ S8 & \(0.8313\pm 0.1444\) & \(0.8377\pm 0.1441\) & \(0.8338\pm 0.1331\) \\ S9 & \(0.7063\pm 0.0979\) & \(0.7278\pm 0.0986\) & \(0.6842\pm 0.1291\) \\ \hline mean \(\pm\) std & \(0.8292\pm 0.1321\) & \(0.8419\pm 0.1287\) & \(0.8256\pm 0.1413\) \\ \hline  & \multicolumn{3}{c}{**All Participants**} \\  & **Accuracy** & **AUC** & **F1-Score** \\ \hline mean \(\pm\) std & \(0.7563\pm 0.0361\) & \(0.7581\pm 0.0375\) & \(0.7900\) \\ \hline  & \multicolumn{3}{c}{**Individual vs. Remaining Participants**} \\  & **Accuracy** & **AUC** & **F1-Score** \\ \hline S1 & \(0.9186\) & \(0.9188\) & \(0.9192\) \\ S2 & \(0.7875\) & \(0.7875\) & \(0.7875\) \\ S3 & \(0.5938\) & \(0.5941\) & \(0.6061\) \\ S4 & \(0.7750\) & \(0.7757\) & \(0.7692\) \\ S5 & \(0  
Furthermore, one may argue that the observed small differences in latency, steepness, and area of the VEPs could be explained by varying attention or vigilance and, consequently, would not be caused by the different colors. However, due to the selected order of the stimulus presentation, it is very unlikely that varying attention and vigilance cause the differences. As stated in Section 2 and depicted in Figure 2, the colors were represented in a random order (e.g., red, red, green, red, green, green, red,...) and not block-wise (e.g., red, red, red,..., red, green, green, green,..., green). Therefore, fading attention should equally impact the VEPs of both colors.  
Moreover, we derived VEPs only from the occipital lobe (OZ), since it was not the aim of our study to diagnose any malfunction of visual signal processing in the brain, but only on the terminal processing of the optical signal. It is known that processing of optical impressions takes place in the area of the occipital lobe, which is why this brain region was used for the measurements. However, it cannot be ruled out that an even better classification might be possible using other brain regions, which should be investigated in the future.