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.

PIGEONS WERE TRAINED IN A GO/NO-GO TASK TO discriminate a major triad from four other chord triads. These latter chords were constructed by altering the third or fifth of the triad by one semitone, creating minor, suspended fourth, augmented, or flat five chords. Experiment 1 used a C root to test these chords. Experiment 2 examined the discrimination of these chords using the D root. Pigeons could discriminate these harmonically complex triads, with manipulations of the fifth supporting better discrimination than manipulations of the third. The augmented chord was perceived as the most dissimilar from the major chord and the suspended fourth chord as the most similar. A combination of attention to sensory consonance and absolute properties of the chords is suggested to account for the results. Comparable human results suggested some overlap in their perception of harmonic elements, but a considerable difference in their flexibility to use this information across different contexts.