ERPs associated with tonal expectations

Previous studies have reported various ERPs components elicited by violations of tonal expectations. Depending on the experimental task and material, these components included positive (P300-like components) and negative (N1, MMN, ERAN, N5) components.

One of the first ERPs associated with tonal expectations has been observed by Besson and Faïta (1995). Participants (musicians and non-musicians) listened to familiar and non-familiar melodies ending on a tonally expected tonic tone, a less expected diatonic tone, or an unexpected out-of-key tone, and they had to judge if the melodies were familiar or not and if their last note was congruous or not. A late positive component (LPC) – distributed centroparietally and of maximal amplitude around 600 ms - was evoked by out-of-key and diatonic tones compared to tonic tones. The LPC was larger for out-of-key vs. tonic than for diatonic vs. tonic tones, its amplitude was larger for familiar than for non-familiar melodies, and it was larger and its latency was earlier for musicians than for non-musicians. A late parietal positive component (P600) was also observed within chord sequences for out-of-key chords (Patel, Gibson, Ratner, Besson, & Holcomb, 1998). Participants judged whether the chord sequences were “acceptable” or “unacceptable”. The observed LPCs had larger amplitude for the out-of-key chords that were the more distant to the key of the chord sequences. A comparable but earlier component, the P3b, was observed by Janata (1995) for unexpected chords ending 3-chord sequences. Unexpected chords were either weakly unexpected minor relative chords or strongly unexpected chords of a distant tonality. Participants had either to judge by pressing a key if the final chord was “the best possible resolution” (p.162) (“response” condition), or had just to quietly think the answer to themselves (“no-response” condition). Unexpected chords elicited a posterior P3b (peaking at 450 ms) in the “response” condition only. Like the P600, the P3b appeared to be sensitive to the degree of violation of the tonal expectation, with a larger amplitude for distant chords than for minor relative chords and for expected tonic chords. These studies indicate that tonal expectations can be investigated by tracking the strength of tonal violations with a late parietal positive ERP component (LPC/P600 or P3b).

Negative components (ERAN and N5) have been reported in a series of studies by Koelsch and collaborators using chord sequences where, in comparison to an expected tonic chord, an unexpected Neapolitan sixth chord (Koelsch, Gunter, Friederici, & Schröger, 2000; Koelsch & Mulder, 2002), a supertonic chord or a double dominant chord (Koelsch, Jentschke, Sammler, & Mietchen, 2007; Koelsch & Sammler, 2008) evoked an early-right (or bilateral) negativity (ERAN), fronto-temporal and peaking around 200 ms. Like the LPC, the amplitude of ERAN was found to depend on the degree of tonal violation (Koelsch et al., 2000; Leino, Brattico, Tervaniemi, & Vuust, 2007). The ERAN was observed even when participants’ attention was not focused on the chord violation, i.e. when they had either to detect an infrequent timbre change (Koelsch et al., 2000) or to ignore the auditory stimuli (Koelsch et al., 2002). When participants had to detect the chord violations (Koelsch & Mulder, 2002; Koelsch, Jentschke, Sammler, & Mietchen, 2007), a following P3b comparable to the positive components observed by Besson and Faïta (1995), Janata (1995), and Patel et al. (1998) was observed. In addition, the ERAN could be followed by a frontal negativity peaking around 550 ms (N5) (Koelsch et al., 2000; Loui et al., 2005). This component has been interpreted as reflecting the integration of musical events into their tonal context (Koelsch et al., 2000).