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 2
nd tones
(M = -0.71 μV, SD = 0.56 μV) was significantly less negative than that of the 1
st 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 2
nd to the 3
rd 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 1
st to 10
th tones (
F1,36 = 17.06,
P < .001,
MSE = 4.40,
ηp2 = 0.32). However, no significant linear trend was observed across the 2
nd to 10
th tones (
F1,36 = 0.08,
P = .78,
MSE = 0.02,
ηp2 = 0.002), suggesting that the initial amplitude decrement observed from the 1
st to 2
nd tones did not continue across subsequent tones (Figure 2a).