## 5 Results  
A linear mixed-effects model with three variables was used to investigate the relation of the CEA values to subject's health condition, stimulus intensities (SIs) and auditory mask use with a random factor corresponding to subjects to account for within-subject variability. The subject's health condition (two levels--healthy/epileptic) is a simple categorical variable, while the SI and the auditory mask use during the stimulations are repeated measures with eight and two levels, respectively. The procedure indicated that the CEA values were not different between the subject health conditions (F = 0.819, \(p\) = 0.366), while they differed with the use of the auditory mask (F = 21.295, \(p\) < 0.001) and across the SI levels (F = 7.246, \(p\) < 0.001). Additionally, the interaction term between the mask and SI variables was determined to be statistically significant (F = 9.690, \(p\) < 0.001). Pairwise comparisons (LSD test) showed that the mask and no mask conditions were statisticallysignificant different for the cases of SI = 40, 50, 60, 70 (\(p\) = 0.010, \(<\)0.000, 0.002, \(<\)0.000, respectively), while no difference was observed for the cases of SI = 0, 30, 35 and 80 (\(p\) = 0.192, 0.424, 0.124, 0.750, respectively). Based on these results, in the ensuing analyses, we pool together the epileptic and healthy groups to achieve a larger sample size and higher statistical power, and we concentrate mostly on the comparison of use of auditory mask vs. no mask case. Figure 5 presents results for CEA as a function of SI. Figure 5a shows the CEA values for all subjects and cases individually, along with exponential mode fits (CEA(SI) = a\(e^{b\cdot\text{SI}}\)) separately for the cases of auditory mask and no mask. It is evident that the two exponential fits are different from each other, validating further the ANOVA results. The exponential factor for the case of auditory mask is b = 0.4022 (CI: 0.140, 0.664), while for the case of no mask is almost double that, with b = 0.737 (CI:0.465, 1.009). The constant terms are comparable for both cases, with a = 0.565 (CI: 0.478, 0.653) and a = 0.538 (CI: 0.461, 0.614) respectively. In Figure 5b, we show the average CEA per SI for the two cases. With no mask, CEA increases almost linearly with respect to SI. On the other hand, the mask keeps CEA relatively constant for all SIs, except for SI = 80%, where we observe an abrupt increase. Figure 5c depicts the percentage decrease in CEA with the use of the mask, which ranges from around 20% for SIs = 30-40% to 30% for SI = 70%. Again, we note that for SI = 80%, there is minimal decrease. In Figure 6, we present the global AEPs (average across all subjects) elicited from the stimulations for the different SIs and auditory mask conditions. The Figure also presents the results of cluster-based permutation tests. These tests are used to identify contiguous time points (i.e., time periods, or point clusters) for which signals from two conditions (e.g., evoked potentials) are statistically significant different. Herein, we use these tests to compare the stimulations to the resting condition for the two mask conditions separately, as also to compare the mask/no mask conditions between them for each SI individually. In the panels of the first row, we see that when there is no auditory mask, the sham stimulation deviates statistically significantly (\(p<0.05\)) from the resting condition for SI = 35% and higher with an evident AEP. On the contrary, when the mask is applied (middle row of panels), the sham stimulation cannot be distinguished from the resting condition for SI of up to 50%. Finally, comparing the mask vs. no mask case, significant difference can be observed for SI in the range from 35% to 70%. For SI = 60 and 70%, even though the mask is not able to completely eliminate the AEP, it significantly reduces its amplitude.