Guitar distortion used in rock music modifies a chord so that new frequencies appear in its harmonic structure. A distorted dyad (power chord) has a special role in heavy metal music due to its harmonics that create a major third interval, making it similar to a major chord. We investigated how distortion affects cortical auditory processing of chords in musicians and nonmusicians. Electric guitar chords with or without distortion and with or without the interval of the major third (i.e., triads or dyads) were presented in an oddball design where one of them served as a repeating standard stimulus and others served as occasional deviants. This enabled the recording of event-related potentials (ERPs) of the electroencephalogram (EEG) related to deviance processing (the mismatch negativity MMN and the attention-related P3a component) in an ignore condition. MMN and P3a responses were elicited in most paradigms. Distorted chords in a nondistorted context only elicited early P3a responses. However, the power chord did not demonstrate a special role in the level of the ERPs. Earlier and larger MMN and P3a responses were elicited when distortion was modified compared to when only harmony (triad vs. dyad) was modified between standards and deviants. The MMN responses were largest when distortion and harmony deviated simultaneously. Musicians demonstrated larger P3a responses than nonmusicians. The results suggest mostly independent cortical auditory processing of distortion and harmony in Western individuals, and facilitated chord change processing in musicians compared to nonmusicians. While distortion has been used in heavy rock music for decades, this study is among the first ones to shed light on its cortical basis.
Major-minor and consonance-dissonance are two profound elements of Western tonal music, and have strong affective connotations for Western listeners. This review summarizes recent evidence on the neurocognitive basis of major-minor and consonance-dissonance by presenting studies on their processing and how it is affected by maturation, musical enculturation, and music training. Based on recent findings in the field, it is proposed that both classifications, particularly consonance-dissonance, have partly innate, biologically hard-wired properties. These properties can make them discriminable even for newborn infants and individuals living outside the Western music culture and, to a small extent, reflect their affective connotations in Western music. Still, musical enculturation and active music training drastically modify the sensory/acoustical as well as affective processing of major-minor and consonance-dissonance. This leads to considerable variance in psychophysiological and behavioral responses to these musical classifications.