The higher the farther: distance-specific referential gestures in chimpanzees (Pan troglodytes).

Chloe Gonseth,Masaki Tomonaga,Fumito Kawakami,Etsuko Ichino

doi:10.1098/rsbl.2017.0398

Abstract

Referential signals, such as manual pointing or deictic words, allow individuals to efficiently locate a specific entity in the environment, using distance-specific linguistic and/or gestural units. To explore the evolutionary prerequisites of such deictic ability, the present study investigates the ability of chimpanzees to adjust their communicative signals to the distance of a referent. A food-request paradigm in which the chimpanzees had to request a close or distant piece of food on a table in the presence/absence of an experimenter was employed. Our main finding concerns the chimpanzees adjusting their requesting behaviours to the distance of the food such that higher manual gestures and larger mouth openings were used to request the distant piece of food. To the best of our knowledge, this is the first study to demonstrate that chimpanzees are able to use distance-specific gestures.

Highlights

Referential signals, such as manual pointing or deictic words, are a crucial component of human communication as they play a central role in social skills and language acquisition [1,2]
The distance of a referent is encoded at a lexical level of language processing [5] as well as at a motor level of language processing [6]
Eight chimpanzees living at the Primate Research Institute of Kyoto University, Japan [16] were individually tested in an indoor room, separated from experimenters by railings made of metallic bars

Summary

Background

Referential signals, such as manual pointing or deictic words, are a crucial component of human communication as they play a central role in social skills and language acquisition [1,2]. These signals are intended to direct the attention of others to specific external entities and to share attention, feelings, and thoughts about them [3]. Distance encoding is a robust feature of the human referential system, present in all aspects of multimodal pointing Identifying this encoding in the signalling behaviours of our closest evolutionary relatives could provide valuable information regarding the emergence and mechanisms of deixis. If distance encoding is already present in chimpanzees, distance-specific oral and manual gestures should be observed

Methods

Results and discussion

AV alone near far distance