1.3 Expectation Control and the Present Study
Importantly, previous studies have suggested that stimulus expectations, which stem from statistical regularities in the environment (Todorovic et al., 2011), can influence components related to adaptation and MMN. For instance, studies have shown that the repetition of stimuli can lead to enhanced N1 amplitudes when participants expect the stimuli (Hari et al., 1979). Additionally, the consistent pairing of standards and deviants may induce perceptual grouping even with long stimulus onset asynchronies (SOAs), potentially affecting MMN amplitudes (Herholz et al., 2009). Explicit top-down expectations have been found to diminish MMN responses (Chennu et al., 2013; Costa-Faidella et al., 2011b; Lecaignard et al., 2021). Recent evidence has suggested that participant-generated stimulus expectations can modulate adaptation effects, even in the absence of attentional involvement (e.g., Barbosa & Kouider, 2018; Kuravi & Vogels, 2017; Todorovic et al., 2011). These findings highlight the role of top-down processing in shaping the adaptation effects.
Based on the findings mentioned above, controlling for stimulus expectations is crucial when investigating adaptation effects. However, experimental constraints may inadvertently modify expectations. For example, in typical MMN experiments, consecutive occurrences of deviants are often avoided, and a maximum number of tone repetitions is enforced. These constraints may lead participants to generate expectations regarding whether the next stimulus will be a deviant or standard, potentially influencing adaptation and MMN components. To address this, the present study implemented an experimental paradigm with minimal constraints on stimulus arrangements to control subjective expectations by maintaining objective predictability. Specifically, stimuli were presented with a stable probability (85% standard, 15% deviant) and extended sequences of up to 30 standards, ensuring a pure measurement of adaptation unaffected by participant expectations.
The present study used initial adaptation to describe the amplitude decrease from the 1st to the 2nd tones and subsequent adaptation to capture the decrease from the 2nd to the final tones in each sequence of identical stimuli. Through an auditory experimental paradigm with controlled expectations, the present study addresses two primary research questions: 1) How do the patterns of initial and subsequent adaptation patterns manifest in the N1 and P2 components? 2) To what extent can these adaptation patterns elucidate the MMN? These two research questions were examined using an EEG experiment in healthy adults, coupled with adaptation pattern, correlation, and regression analyses.
Regarding the first research question, we predicted that the N1 and P2 components would show reduced amplitudes in response to the initial tones, indicative of adaptation, in line with previous findings (Budd et al., 1998; Rosburg & Sörös, 2016). However, we anticipated potential increases in P2 amplitudes due to the influence of RP, suggesting a memory trace effect related to the model adjustment account (Haenschel et al., 2005).
Concerning the second research question, we predicted positive correlations between MMN and adaptation effects observed in the N1 component, as well as negative correlations between MMN and adaptation effects observed in the P2 component. Furthermore, we hypothesized that both initial and subsequent adaptation effects would be important predictors of the MMN, as suggested by the predictive coding account, which posits the involvement of both adaptation and the model adjustment mechanisms in MMN generation.