Linguistic laws of brevity: conformity in Indri indri

Abstract

Vocal and gestural sequences of several primates have been found to conform to two general principles of information compression: the compensation between the duration of a construct and that of its components (Menzerath-Altmann law) and an inverse relationship between signal duration and its occurrence (Zipf's law of abbreviation). Even though Zipf's law of brevity has been proposed as a universal in animal communication, evidence on non-human primate vocal behavior conformity to linguistic laws is still debated, and information on strepsirrhine primates is lacking. We analyzed the vocal behavior of the unique singing lemur species (Indri indri) to assess whether the song of the species shows evidence for compression. As roars have a chaotic structure that impedes the recognition of each individual utterance, and long notes are usually given by males, we focused on the core part of the song (i.e., the descending phrases, composed of two-six units).Our results indicate that indris' songs conform to Zipf's and Menzerath-Altmann linguistic laws. Indeed, shorter phrases are more likely to be included in the song, and units' duration decrease at the increase of the size of the phrases. We also found that, despite a sexual dimorphism in the duration of both units and phrases, these laws characterize sequences of both males and females. Overall, we provide the first evidence for a trade-off between signal duration and occurrence in the vocal behavior of a strepsirrhine species, suggesting that selective pressures for vocal compression are more ancestral than previously assumed within primates.

Compression principle and Zipf’s Law of brevity in infochemical communication

“…We have validated with unprecedented detail, by studying more than 36 000 infochemical interactions, that Zipf’s Law of brevity operates at interspecies infochemical communication. Those results are in line with precedent studies in language, and other communication systems [18,20–22,53–55], suggesting the universality of this linguistic law and the principle of compression, from which it derives. Nevertheless, we have found no evidence that Zipf’s Law of brevity holds in intraspecific chemical communication—pheromones.…”

“…Those results are in line with precedent studies in language, and other communication systems [18,[20][21][22][53][54][55], suggesting the universality of this linguistic law and the principle of compression, from which it derives. Nevertheless, we have found no evidence that Zipf's Law of brevity holds in intraspecific chemical communication-pheromones.…”

Untitled

“…We have shown that Menzerath's law, but not MAL, arises also for a simple memoryless source with three emitted symbols. This observation shows that the mere Menzerath's law is not a property that distinguishes complex systems, which makes necessary to review and revise some previous comparative studies in human and non-human communication [21][22][23][24][25][26][27][28] or in other fields including genomics or ecology [17,18,68]. Moreover, as we have shown analyzing the Standarized Gutenberg Corpus on 21 languages, beyond a certain length of words, the inverted regime is found indeed, providing new evidence for the applicability of MAL.…”

“…The memoryless source model reproduces the negative correlation between the size of the constituents and the size of the whole. Therefore, recent studies that have found Menzerath's law in the communication systems of some animal species and attributed it to a certain complexity of communication systems of these living beings [21][22][23][24][25][26][27][28] should be carefully reviewed. The memoryless source model considered in this paper is a baseline model operating in terms of grapheme classes but it could be easily generalized and extended to other types of constituents and substructures such as phonemes, sentences, or breath groups that are typical of speech.…”

“…Besides, similar analyses can be extended to any system that forms a hierarchy of units of different levels. Consequently, Menzerath's law has also been observed in genomes [17][18][19], protein domains [20], penguin vocalizations [21], chimpanzee gestural communication [22] and primate vocalizations [23][24][25][26][27], including strepsirrhine species [28]. It is related to compression principles [23,29] and explained in terms of oral communication as follows: Given that lungs' air capacity is limited, when longer words are vocalized then their constituents tend to be more compressed because the speaker must 'hurry' to finish articulating the word before running out of air [12,25].…”