3.1 N1 Adaptation
The adaptation curve for the first ten tones, derived from the average N1 peak data, was plotted based on the peak amplitudes in the N1 time window. A steep decrease in N1 amplitude was observed between the 1st and 2nd tones, followed by a plateau (Figure 2a). Paired-sample t-tests revealed that the N1 amplitude of the 2nd tones (M = -0.71 μV, SD = 0.56 μV) was significantly less negative than that of the 1st tones (M = -1.51 μV, SD = 0.77 μV; t36 = -6.68, P < .001, d = 0.72). Additionally, there was a rebound effect, indicated by a significant increase in the N1 amplitude from the 2nd to the 3rd tones (M = -0.99 μV, SD = 0.60 μV; t36 = 3.91, P < .001, d = 0.43). No other significant difference was observed in subsequent tone pairs (all P > .007 based on the Holm-Bonferroni correction).
Furthermore, a significant linear trend was evident across the 1st to 10th tones (F1,36 = 17.06, P < .001, MSE = 4.40, ηp2 = 0.32).  However, no significant linear trend was observed across the 2nd to 10th tones (F1,36 = 0.08, P = .78, MSE = 0.02, ηp2 = 0.002), suggesting that the initial amplitude decrement observed from the 1st to 2nd tones did not continue across subsequent tones (Figure 2a).