Abstract
Many drum communication systems around the world transmit information by emulating tonal and rhythmic patterns of spoken languages in sequences of drumbeats. Their rhythmic characteristics, in particular, have not been systematically studied so far, although understanding them represents a rare occasion for providing an original insight into the basic units of speech rhythm as selected by natural speech practices directly based on beats. Here, we analyse a corpus of Bora drum communication from the northwest Amazon, which is nowadays endangered with extinction. We show that four rhythmic units are encoded in the length of pauses between beats. We argue that these units correspond to vowel-to-vowel intervals with different numbers of consonants and vowel lengths. By contrast, aligning beats with syllables, mora or only vowel length yields inconsistent results. Moreover, we also show that Bora drummed messages conventionally select rhythmically distinct markers to further distinguish words. The two phonological tones represented in drummed speech encode only few lexical contrasts. Rhythm thus appears to crucially contribute to the intelligibility of drummed Bora. Our study provides novel evidence for the role of rhythmic structures composed of vowel-to-vowel intervals in the complex puzzle concerning the redundancy and distinctiveness of acoustic features embedded in speech.
Highlights
The human voice can produce rich and varied acoustic signals for transmitting information, but normally only up to a few hundred metres
Using acoustically simple signals that propagate well in natural environments across long distances comes with the challenge of being able to represent only a fraction of the acoustic features of spoken language, as produced by the human voice, without rendering speech incomprehensible [1]
The analysed data originate from an extensive corpus of manguaré and spoken Bora collected as part of a large-scale project documenting Bora linguistic and cultural heritage [17]
Summary
The human voice can produce rich and varied acoustic signals for transmitting information, but normally only up to a few hundred metres. Drum communication systems like that of the Bora people of the northwest Amazon can extend this range by a factor of up to 100 through emulating speech in sequences of drumbeats. Using acoustically simple signals that propagate well in natural environments across long distances comes with the challenge of being able to represent only a fraction of the acoustic features of spoken language, as produced by the human voice, without rendering speech incomprehensible [1]. Systems of long-distance communication emulating speech with drummed beats or whistles developed by traditional societies represent unique natural laboratories for exploring the relative distinctiveness of various linguistically relevant acoustic features. For Bora, it has even been claimed that rhythm plays no role in drummed speech [12], wrongly as we will argue
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