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.rhythm perception | time encoding | sound asynchrony perception | auditory perception | mismatch negativity T he perception of music involves the processing of multiple simultaneous sounds, including the perceptual organization of components originating from one instrument into a single "auditory object" (1) and their segregation from components that originate from other instruments. The first stage of this process occurs in the inner ear and involves the decomposition of incoming sound by frequency, resulting in frequency-to-place mapping (tonotopy) along the length of the cochlear partition (2).A series of recent studies has suggested that these and other basic properties of the auditory system, which are shared by a wide variety of species, may help account for some fundamental aspects of Western music, including the dominance of high-register instruments (i.e., instruments with high fundamental frequencies) in carrying the melody (3-7), as well as the dominance of low-register instruments (such as bass or bass drum) in defining the meter or rhythm (8). In the latter case, a study by Hove et al. (8) involving both behavioral and EEG experiments reported that time encoding was superior for low-vs. high-pitched sounds and suggested that this superior time encoding could explain why low instruments generally lay the rhythm in music.The suggestion that superior time encoding of low pitches can explain aspects of Western music is intriguing. However, it runs contrary to the results from studies of many other types of auditory temporal processing, including gap detection (9), amplitude-modulation detection (10) and discrimination (11), and duration discrimination (12)...

Neural tracking of the musical beat is enhanced by low-frequency sounds

“…Greater sensitivity to the temporal misalignment of low tones was observed when they were presented earlier than expected, which suggested better time encoding for low sounds. These results were replicated and extended by Wojtczak et al ( 13 ), who showed that the effect was related to greater tolerance for low-frequency sounds lagging high-frequency sounds than vice versa. However, these studies only provide indirect evidence for the effect of low sounds on internal entrainment to rhythm, inferred from brain responses to deviant sounds.…”

“…There has been a recent debate as to whether evolutionarily shaped properties of the auditory system lead to superior temporal encoding for bass sounds ( 12 , 13 ). One study using electroencephalography (EEG) recorded brain responses elicited by misaligned tone onsets in an isochronous sequence of simultaneous low- and high-pitched tones ( 12 ).…”

Preferred Tempo and Low-Audio-Frequency Bias Emerge From Simulated Sub-cortical Processing of Sounds With a Musical Beat

“…This bias provides a potential neurobiological reason for why low-frequency instruments carry the beat in some music (for example see Snyder and Krumhansl, 2001 ). However, it is tricky to test this perceptually; multiple instruments often play simultaneously on the beat, and cochlear delays can explain biases for simultaneous events (Wojtczak et al, 2017 ). Our stimuli used amplitude modulations at distinct tempi and phases to reduce the effects of simultaneous events, and we quantified the bias using the synchronization strength of neural activity rather than timing to specific events.…”

“…Subjects also identify beats in piano ragtime music better when the left hand (lower frequency) is played alone than when the right hand (higher frequency) is played alone, although this could be due to the regularity of the left hand for this type of music (Snyder and Krumhansl, 2001 ). A low-frequency bias for beat timing could result from cochlear processing, where low frequencies cause a greater spread of excitation than higher frequencies (Hove et al, 2014 ), but these effects need to be disambiguated from cochlear delays that can produce similar biasing effects for simultaneous events (Wojtczak et al, 2017 ). For repeating “frozen” noise, where the noise signal was identical on each repetition, subjects focus on mid-frequency perturbations in the signal, between 300 and 2,000 Hz, when tapping along with the repetition (Kaernbach, 1993 ).…”

Neural bases of rhythmic entrainment in humans: critical transformation between cortical and lower‐level representations of auditory rhythm

“…Relatedly, recent models have been proposed to quantify the extent to which beat perception could be explained by early auditory sensory processing in brainstem auditory nuclei that we share with other animals (Rajendran et al ., ). This hypothesis is also related to a line of research investigating the extent to which musical conventions and habits are determined by evolutionarily shaped human physiology (Hove et al ., ; Merchant & Honing, ; Wojtczak et al ., ).…”