Speech is processed via rhythm
Researchers have studied the drum language of the Boras in the Amazon region, which not only imitates the melody of words and sentences, but also their rhythm. This suggests that speech rhythm plays a more important role in language processing than previously assumed.
The human voice can generate a variety of acoustic signals to transmit information. However, this transmission normally only has a range of around 200 meters. The Boras, an indigenous group of around 1500 members who live in small communities in the Amazon rainforest of Colombia and Peru, can increase this range a hundredfold by imitating words and sentences with drum beats. The Boras use pairs of Manguaré drums for this purpose. These are traditionally made from individual wooden trunks, each two meters long, by burning them out. Each drum can produce two pitches, making a pair of drums four in total.
The Boras use the Manguaré drums in two different ways: In musical mode, they play previously memorized drum sequences with little or no variation at rituals and festivals. In speech mode, on the other hand, they transmit relatively informal messages and public announcements. "Manguaré is used, for example, to ask someone to bring something or do something, to announce the result of alcohol-free drinking competitions or the arrival of visitors," says Seifart, who was part of the former Department of Linguistics at the Max Planck Institute in Leipzig, where much of the recently published study was conducted. "In this mode, only two pitches are used, and each drumbeat corresponds to one syllable of a spoken bora word. The messages contain an average of 15 words, or 60 drum beats."
An astonishing variety of messages can be conveyed by imitating tone and rhythm, formulating the messages in such a way as to clear up any remaining ambiguities. "Rhythm proves crucial in Bora in distinguishing words," says Seifart. "There are four rhythmic units, depending on the length of the pauses between the individual beats. These units correspond to vowel-to-vowel intervals with different numbers of consonants and vowel lengths. The two phonological tones represented by drummed speech contribute little to the meaning. The rhythm is therefore decisive for the intelligibility of the drummed bora."
According to the research team, this is further evidence of the role of rhythmic structures consisting of vowel-to-vowel intervals in the complex interplay of redundant and distinctive acoustic features of spoken language.
