4. Discussion
Neural adaptation serves as a fundamental mechanism through which the brain utilizes previous experiences with stimuli (e.g., Grill-Spector et al., 2006). While previous studies in the auditory domain have predominantly focused on examining adaptation through stimulus pairs or series of repetitions, the present study delved deeper into the adaptation patterns of N1 and P2, comparing initial versus subsequent repetitions. Unlike previous MMN investigations that employed varied paradigms to differentiate the adaptation and model adjustment accounts of MMN (e.g., Jacobsen & Schröger, 2001), the present study investigated the interplay between MMN and adaptation patterns in N1 and P2. Crucially, expectations were controlled by presenting tones with fixed probabilities with extended sequences. The results unveiled adaptation effects within the N1 component during initial tone repetitions. Conversely, the P2 amplitude exhibited a linear increase with successive repetitions, suggestive of the model adjustment effect. Notably, MMN amplitudes were mainly influenced by the N1 adaptation effect induced by the initial tones and the continuous P2 adaptation effect elicited by subsequent tones. Further elucidation of these adaptation patterns is provided below.