"Adaptive Functions of Musical Signals" [PIANO + ME] @ Psychology & Music Conference, Belgrade 2022
Channel: David M. Schruth
Date: 2022-12-12

An outline of of the state of David Schruth's research into several possibly adaptive functions of musical signals in various animal taxa, including humans. A presentation at the second international conference of "Psychology and Music Conference - Interdisciplinary Encounters" at the University of Belgrade on  October 29, 2022
---------------------------------------------------------------------------------------------------------------
ABSTRACT:

Music is a complex acoustic phenomenon produced primarily by a single species, namely humans. However, many other species produce sounds (e.g. song-like calls and music-like note progressions) which overlap considerably with the acoustic features fundamentally present in most human societies. A small but robust subset of key features of human music arguably includes tone, interval, rhythm, repetition, transposition, and syllabic diversity. These can be found to varying degrees in the calls of non-human primates—and, when analyzed via exploratory statistical methods, have yielded a possibly zoologically applicable index of musicality useful for comparing origins of this phenomenon across species. 

Equipped with this newly developed acoustic (syllable) reappearance diversity index [ARDI] of musicality, I endeavored to compare various levels of musical output of species with aspects of their unique ecological settings. Typical factors influencing vocalization, such as morphology (e.g. mass, age, sex, and dimorphism), immediate behavioral contexts (e.g. contact, foraging, and display), as well as more habitual ones (e.g. sex ratio, group size, monogamy, diurnality, arboreality, territoriality, predation, and acrobatic locomotion) were considered. 

ARDI was developed using PCA on the above-mentioned six features [see Background] prevalent in human music utterances. Using ARDI scores on non-human primate vocalizations in conjunction with typical song counts in other species (e.g. whales and birds), I was able to interrogate (e.g. using multivariate linear regression) the above array of candidate ecological variables [see Aims] as evolutionary instigative. For primates, specifically, I was also able to compare brain component volumes (n=42) with vocal complexity.

Many of the above factors were found to have a moderate influence on complex vocal signaling behavior across species. Most of these factors had positive associations with the exception of group size (mixed), sex (neutral), and predation (negative). That is, both sexes of members of small, family-sized groups that experience less predation tend to make more musical vocalizations. Also interesting is that these species tend to live in chemically dilute environments and have reduced olfactory neural capacities. In primates the schizocortex and hippocampus have marginally positive correlations with musical (high ARDI) calls, suggesting a possible role in spatial orientation as well. Most convincingly, however, visual areas (e.g. visual cortex and LGN) are even more strongly correlated with musical calling in primates, suggestive of a more locomotion relevant signaling function. 

Primarily, animals appear to have initially evolved complex vocalizations to compensate for a loss of olfaction in chemically dilute environments. This compensation may have manifested as articulation and discretization of distinct syllabic acoustic structures. Secondarily, animals appear to use musical calls to remain in acoustic contact and spatially orient with conspecifics during foraging and ranging in visually occluded environments. This second ecological pressure likely engendered highly intervalic and transpositional elements in calls to compensate for ambient noise of acoustic sound-scapes. Lastly, effective anti-predational tactics, in many vocally communicating species, could have not only required higher proficiency in evasive locomotion and associated precision in “spatio-motive landing,” but also emboldened an expansion of such intra-group contact calls into more externally facing territorial displays. This third ecological pressure, influencing the co-evolutionary interplay of motor-eye coordination with musical-acoustic output, may have augmented levels of precision in reappearance (both repetition and transposition) for an increasingly diverse assemblage of spectral shapes.