3.4 Flash rate scoring
The ANOVA revealed a significant main effect of AM (F (1,24) = 8.487, p = 0.008, ηp2 = 0.261) condition, indicating a higher perceived flash rate for sinusoidal (16.02 ± 3.19) than for AM (13.34 ± 3.61) stimulations. The main effect of intensity was marginally significant (F (1,24) = 3.446,p = 0.076, ηp2 = 0.126), with a marginal interaction between polarity and intensity (F (2,48) = 2.885, p = 0.066, ηp2 = 0.107). Further tests on this effect revealed that only in the anodal otDCS participants score the flash of suprathreshold stimulations as faster than threshold stimulations (p = 0.011). However, ANOVA did not reveal the significance of polarity (F (2,48) = 0.256, p = 0.775, ηp2 = 0.011), or any 2-way and 3-way interactions (polarity × AM: F (1.5,35.6) = 0.580, p = 0.516, ηp2 = 0.024; AM × intensity:F (1,24) = 0.508, p = 0.483, ηp2 = 0.021; polarity × AM × intensity: F (2,48) = 1.009, p = 0.372, ηp2 = 0.040; Figure 2D).
3.5 Confidence of flash rate scoring
ANOVA on the confidence levels revealed a significant main effect of intensity (F (1,24) = 11.613, p = 0.002, ηp2 = 0.326) and the 3-way interaction between polarity, AM, and intensities (F (2,48) = 4.224, p = 0.020, ηp2 = 0.150). The statistics yielded a higher confidence rating for the suprathreshold (5.74 ± 0.80) than for the threshold (5.36 ± 0.91) stimulation, and the effect was most pronounced in the AM stimulation of anodal otDCS (p = 0.007) and sinusoidal stimulation of tACS (p = 0.04). The analysis did not reveal other main effects (polarity: F (1.4,34.5) = 0.403,p = 0.604, ηp2 = 0.017; AM:F (1,24) = 0.011, p = 0.919, ηp2 = 0.000; polarity × AM:F (2,48) = 2.059, p = 0.139, ηp2 = 0.079; polarity × intensity:F (2,48) = 2.715, p = 0.076, ηp2 = 0.102; AM × intensity:F (1,24) = 0.006, p = 0.939, ηp2 = 0.000; Figure 2E).