Abstract
Music perception builds on expectancy in harmony, melody, and rhythm. Neural responses to the violations of such expectations are observed in event-related potentials (ERPs) measured using electroencephalography. Most previous ERP studies demonstrating sensitivity to musical violations used stimuli that were temporally regular and musically structured, with less-frequent deviant events that differed from a specific expectation in some feature such as pitch, harmony, or rhythm. Here, we asked whether expectancies about Western musical scale are strong enough to elicit ERP deviance components. Specifically, we explored whether pitches inconsistent with an established scale context elicit deviant components even though equally rare pitches that fit into the established context do not, and even when their timing is unpredictable. We used Markov chains to create temporally irregular pseudo-random sequences of notes chosen from one of two diatonic scales. The Markov pitch-transition probabilities resulted in sequences that favored notes within the scale, but that lacked clear melodic, harmonic, or rhythmic structure. At the random positions, the sequence contained probe tones that were either within the established scale or were out of key. Our subjects ignored the note sequences, watching a self-selected silent movie with subtitles. Compared to the in-key probes, the out-of-key probes elicited a significantly larger P2 ERP component. Results show that random note sequences establish expectations of the “first-order” statistical property of musical key, even in listeners not actively monitoring the sequences.
Highlights
In music, properties such as pitch, harmony, and rhythm have statistically regular structures that build expectations about future events
The same physical stimulus evoked these event-related potentials (ERPs) in both key contexts, peaks around ms (P2) amplitudes are larger when the stimulus is an incongruent, out-of-key tone than when it fits in the key context
Scalp topographies at three times (97.7 ms, 199.2 ms, and 339.8 ms) corresponding to the N1, P2, and N2 localpeak timings derived from electrode Cz are shown below the time-course ERPs
Summary
Properties such as pitch, harmony, and rhythm have statistically regular structures that build expectations about future events. One study showed that occasionally replacing either the third or the last chord in a five-chord sequence with a musical chord that violates the established tonal context results in a negative ERP with a peak latency of 150–180 ms, topographically located in right anterior scalp sensors (Koelsch et al, 2000; Tillmann et al, 2003). This expectancy effect was stronger both when the irregular chord was in the final position in a sequence and when it was least expected given the musical context (Koelsch et al, 2000). Both the MMN and ERAN can be seen even if listeners are not actively attending to the ongoing note sequences (Brattico et al, 2006; Koelsch, 2009; Maidhof et al, 2010)
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