Neural correlates of sensory consonance and dissonance in primate primary auditory cortex.

Abstract

The perception of consonance and dissonance of isolated chords (sensory consonance/dissonance) is fundamental to music appreciation. Consonant chords are composed of tones related to each other by simple frequency ratios (e.g., perfect fifth 3:2), whereas dissonant chords are composed of tones related to each other by complex ratios (e.g., minor second 256:243). Dissonance is thought to be due to the perception of beats (modulation frequencies < 20 Hz) or roughness (modulation frequencies from 20–250 Hz), which occur when two or more components of a complex sound are separated from one another in frequency by less than the width of an auditory filter (i.e., critical bandwidth). These unresolved frequency components interact in the auditory periphery to produce amplitude-modulated (AM) fluctuations in the composite waveform envelope. We demonstrate that the magnitude of neuronal phase-locking to these AM fluctuations in primary auditory cortex of awake monkeys correlates with the perceived consonance/dissonance of musical chords and parallels human perception of roughness. This correlation is displayed by population activity, as measured by auditory evoked potentials (AEPs), current source density, and multiunit activity. We further demonstrate that phase-locking of AEPs in Heschl’s gyrus of humans is similar to that seen in the monkey.