Cross-modal constraints in multimodal vocalizations in Siamang (Symphalangus syndactylus)

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Wim Pouw, Mounia Kehy, Marco Gamba, Andrea Ravignani


Gibbons (Hylobatidae) sing loudly, reaching over a hundred Decibels - about the sound level of a rock concert. Qualitative observations report that, during song climaxes, individuals move in a coordinated way with their singing. We hypothesize
that vigorous thorax-loading movements such as brachiation induce physical constraints on the respiratory-vocal system. This coordination and possibly underlying biomechanics have never been studied, leaving a blind spot for a possible shared
variance between vocal and locomotor repertoires that would indicate a co-evolution of two systems. Here, we recorded over a hundred stereotypical multimodal vocal calls from over 7 hours of singing in two captive siamangs (Syndactylus symphalangus), a type of gibbon that are the largest in size. These stereotypical calls coincided with a bodily display during solo singing, and were exclusively performed by juvenile individuals. We used computer vision methods (opencv and deeplabcut) to quantify upper body acceleration of these multimodal displays of two individuals; we found that body acceleration
statistically predicted the nearest peak in the amplitude envelope of the call. The results indicate that Siamang singing likely co-evolved with movement due to physical constraints of pectoral limb-respiratory-vocal interactions, similar to birds, bats, and rodents, as well as humans. This has important implications for the locomotor hypotheses of rhythm origins as our results suggest a biomechanical and basic coupling of vocal systems with the (loco)-motor system: in singing Siamangs, and perhaps humans too, as there are homologies to be drawn between how humans and Siamang move in gestural ways with their vocalizations.



Physical Sciences and Mathematics


Siamang, Locomotor-vocal coupling, locomotion, respiration, Vocalization, Multimodal displays, locomotor-vocal coupling, locomotion, respiration, vocalization, multimodal displays


Published: 2023-07-15 20:03

Last Updated: 2023-10-06 16:40

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CC BY Attribution 4.0 International

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