Recursive music elucidates neural mechanisms supporting the generation and detection of melodic hierarchies

Abstract

The ability to generate complex hierarchical structures is a crucial component of human cognition which can be expressed in the musical domain in the form of hierarchical melodic relations. The neural underpinnings of this ability have been investigated by comparing the perception of well-formed melodies with unexpected sequences of tones. However, these contrasts do not target specifically the representation of rules generating hierarchical structure. Here, we present a novel paradigm in which identical melodic sequences are generated in four steps, according to three different rules: The Recursive rule, generating new hierarchical levels at each step; The Iterative rule, adding tones within a fixed hierarchical level without generating new levels; and a control rule that simply repeats the third step. Using fMRI, we compared brain activity across these rules when participants are imagining the fourth step after listening to the third (generation phase), and when participants listened to a fourth step (test sound phase), either well-formed or a violation. We found that, in comparison with Repetition and Iteration, imagining the fourth step using the Recursive rule activated the superior temporal gyrus (STG). During the test sound phase, we found fronto-temporo-parietal activity and hippocampal de-activation when processing violations, but no differences between rules. STG activation during the generation phase suggests that generating new hierarchical levels from previous steps might rely on retrieving appropriate melodic hierarchy schemas. Previous findings highlighting the role of hippocampus and inferior frontal gyrus may reflect processing of unexpected melodic sequences, rather than hierarchy generation per se.

Hierarchical control as a shared neurocognitive mechanism for language and music

“…Especially, the relationship between linguistic and musical syntax in terms of the fronto-temporal network via the left and right arcuate fasciculus respectively is to be clarified (Friederici, 2019). While the left posterior temporal region is indicated in structure building of linguistic syntax (Matchin & Hickok, 2020), there is evidence that the right posterior temporal region is rather crucial for structure building in musical syntax (Martins et al, 2020).…”

The hearing hippocampus

“…Interestingly, these were the same conditions that elicited the greatest pleasure ratings in listeners. Other fMRI work has been more equivocal as to whether hippocampus tracks uncertainty in auditory sequences (Tobia et al, 2012), and in another study the hippocampal BOLD signal was reduced in tone sequences in which simple or hierarchical rules concerning pitch and duration were violated compared to when they were met (Martins et al, 2020). Disparate findings may relate to functional heterogeneity of hippocampal fields, or position of activity along the long axis.…”

Finding hierarchical structure in binary sequences : evidence from Lindenmayer grammar learning

“…Recent work has used fractal stimuli to explore hierarchical processing in the visual modality (Martins et al, 2015;Martins et al, 2014;, the auditory modality (Martins et al, 2017;Martins et al, 2020), and in the motor domain . In this series of studies, participants were performing a completion task on periodic fractals.…”