Rhythm judgments reveal a frequency asymmetry in the perception and neural coding of sound synchrony

Abstract

In modern Western music, melody is commonly conveyed by pitch changes in the highest-register voice, whereas meter or rhythm is often carried by instruments with lower pitches. An intriguing and recently suggested possibility is that the custom of assigning rhythmic functions to lower-pitch instruments may have emerged because of fundamental properties of the auditory system that result in superior time encoding for low pitches. Here we compare rhythm and synchrony perception between low- and high-frequency tones, using both behavioral and EEG techniques. Both methods were consistent in showing no superiority in time encoding for low over high frequencies. However, listeners were consistently more sensitive to timing differences between two nearly synchronous tones when the high-frequency tone followed the low-frequency tone than vice versa. The results demonstrate no superiority of low frequencies in timing judgments but reveal a robust asymmetry in the perception and neural coding of synchrony that reflects greater tolerance for delays of low- relative to high-frequency sounds than vice versa. We propose that this asymmetry exists to compensate for inherent and variable time delays in cochlear processing, as well as the acoustical properties of sound sources in the natural environment, thereby providing veridical perceptual experiences of simultaneity.