Experimental Evidence for Phonemic Contrasts in a Nonhuman Vocal System.

Sabrina Engesser,Jodie M S Crane,Simon W Townsend,Andrew F Russell,James L Savage,Asif A Ghazanfar

doi:10.1371/journal.pbio.1002171

Abstract

The ability to generate new meaning by rearranging combinations of meaningless sounds is a fundamental component of language. Although animal vocalizations often comprise combinations of meaningless acoustic elements, evidence that rearranging such combinations generates functionally distinct meaning is lacking. Here, we provide evidence for this basic ability in calls of the chestnut-crowned babbler (Pomatostomus ruficeps), a highly cooperative bird of the Australian arid zone. Using acoustic analyses, natural observations, and a series of controlled playback experiments, we demonstrate that this species uses the same acoustic elements (A and B) in different arrangements (AB or BAB) to create two functionally distinct vocalizations. Specifically, the addition or omission of a contextually meaningless acoustic element at a single position generates a phoneme-like contrast that is sufficient to distinguish the meaning between the two calls. Our results indicate that the capacity to rearrange meaningless sounds in order to create new signals occurs outside of humans. We suggest that phonemic contrasts represent a rudimentary form of phoneme structure and a potential early step towards the generative phonemic system of human language.

Highlights

The vast lexicons that characterise human languages are the product of physical and cognitive processes that guide the combination of a limited number of meaningless sounds in a variety of ways to generate new meaning [1,2]
We suggest that phonemic contrasts represent a rudimentary form of phoneme structure and a potential early step towards the generative phonemic system of human language
A major question in language evolution is how its generative power emerged. This power, which allows the communication of limitless thoughts and ideas, is a result of the combinatorial nature of human language: meaningless phonemes can be combined to form meaningful words, and words can be combined to form higher-order, meaningful structures

Summary

Introduction

The vast lexicons that characterise human languages are the product of physical and cognitive processes that guide the combination of a limited number of meaningless sounds (phonemes) in a variety of ways to generate new meaning [1,2]. The meaningless phonemes maintain their acoustic identity across words, and this, paired with the arbitrary relationship between phoneme structure and word meaning, results in words with shared phonemes having distinct semantic content [4]. Such phoneme structure is a basic ingredient of word generation in human language, and when combined with the rules governing assemblages of meaningful words (a syntactic layer), provides much of language’s generative power [5,6,7]. Whilst comparative data from animal communication systems can elucidate early forms of language components, data demonstrating the critical rudiments of phoneme structures outside of humans is lacking

Results

Discussion

Conclusion