1.1 Adaptation
Repeated presentation of the same stimulus typically leads to reduced neural activation, a phenomenon known by various terms such as neural adaptation (Grill-Spector et al., 2006; Ringo, 1996), repetition suppression (Desimone, 1996; Grill-Spector et al., 2006), sensory gating (Boutros & Belger, 1999; Freedman et al., 1987), habituation (Bourbon et al., 1987; Loveless, 1983; c.f. Barry et al., 1992), refractoriness (Berry & Meister, 1998; Budd et al., 1998; Rosburg & Mager, 2021), among others. In the present study, we refer to this phenomenon as adaptation. Adaptation occurs across various stimuli in both visual and auditory domains, such as faces (see Schweinberger & Neumann, 2016 for a review), symbols (e.g., Soltész & Szűcs, 2014), and tones (e.g., Todorovic & de Lange, 2012).
Adaptation can be measured by a decrease in the amplitude of the event-related potential (ERP) components recorded via electroencephalography (EEG) from the scalp. In the auditory modality, ERP components, including N1 and P2, are typically measured at fronto-central electrodes. The N1 component is characterized by a negative deflection occurring roughly between 60–160 ms (Woods, 1995), while the P2 component is a positive deflection peaking around 150–250 ms (Crowley & Colrain, 2004). These components are distributed over fronto-central areas and exhibit a polarity reversal over inferior posterior electrodes when measured against an average reference (Crowley & Colrain, 2004; Fogarty et al., 2020; Näätänen & Picton, 1987; Woods, 1995).
The auditory N1 and P2 adaptations, characterized by a decrement in amplitude, were found in a vast number of studies using pairs of tones or long sequences of tones (e.g., N1: Bourbon et al., 1987; Boutros et al., 1999; Budd et al., 1998; Lagemann et al., 2012; Näätänen & Picton, 1987; Rosburg, 2004; Rosburg & Mager, 2021; Rosburg et al., 2006; N1 and P2: Hari et al., 1982; Herrmann et al., 2016; Peter et al., 2019; Polich, 1986; Rosburg et al., 2022; Rosburg et al., 2010; Sambeth et al., 2004). Regarding the adaptation pattern, most studies have observed an initial N1 decrease, which stabilizes after the 2nd or 3rd sound in a stimulus sequence, with no further decrease for subsequent sounds (e.g., Barry et al., 1992; Bourbon et al., 1987; Boutros et al., 1999; Budd et al., 1998; Lagemann et al., 2012; Rosburg, 2004; c.f. Öhman & Lader, 1972). An initial amplitude decrease has also been observed in the P2 in some studies (Rosburg & Sörös, 2016; Rosburg et al., 2010).