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

Abstract

Prior research has shown that musical beats are salient at the level of the cortex in humans. Yet below the cortex there is considerable sub-cortical processing that could influence beat perception. Some biases, such as a tempo preference and an audio frequency bias for beat timing, could result from sub-cortical processing. Here, we used models of the auditory-nerve and midbrain-level amplitude modulation filtering to simulate sub-cortical neural activity to various beat-inducing stimuli, and we used the simulated activity to determine the tempo or beat frequency of the music. First, irrespective of the stimulus being presented, the preferred tempo was around 100 beats per minute, which is within the range of tempi where tempo discrimination and tapping accuracy are optimal. Second, sub-cortical processing predicted a stronger influence of lower audio frequencies on beat perception. However, the tempo identification algorithm that was optimized for simple stimuli often failed for recordings of music. For music, the most highly synchronized model activity occurred at a multiple of the beat frequency. Using bottom-up processes alone is insufficient to produce beat-locked activity. Instead, a learned and possibly top-down mechanism that scales the synchronization frequency to derive the beat frequency greatly improves the performance of tempo identification.

Auditory cortical representation of music favours the perceived beat

“…It is therefore particularly worth noting the strong correspondences observed here between auditory cortical firing rates and tapping behaviour, and how well these correspondences could be captured by a standard LN model. Our findings suggest that fundamental, low-level mechanisms such as adaptation [13], amplitude modulation tuning [53] and temporal contrasts in STRFs play a formative role in musical beat perception. This is consistent with the idea that the induction of beat is the result of an interaction between 'bottom-up' sensory processes and 'top-down' cognitive ones [54], perhaps through the application of learned and implicit rhythmic priors [6,7] onto an ascending sensory representation [13,53].…”

EEG-based classification of natural sounds reveals specialized responses to speech and music

“…However, 433 the temporal features that generate these responses may differ. Midbrain neuron models with 434 different synaptic parameters optimally capture vowel formant and beat-related information in 435 speech and music respectively (Carney et al, 2015;Zuk et al, 2018). The specializations for 436 speech and music in the auditory cortex may have underpinnings at earlier processing stages in 437 the auditory system.…”

Envelope reconstruction of speech and music highlights unique tracking of speech at low frequencies

“…We then subtracted the spectra from null spectra generated by randomizing the phases in the reconstructions for each subject and averaging these randomized reconstructions (see Zhu et al, 2013;Keshishzadeh et al, 2020) (Figure 6d). From these adjusted spectral values we identified the peaks occurring at the tempo of the music (see Methods) as well as 2 -4x the tempo, since the peak energy may occur at multiples of the expected musical beat frequency of the music based on the acoustics (Ding et al, 2017) or neural activity following subcortical processing (Zuk et al, 2018).…”