Vocalisations provide the opportunity to communicate over great distances and without direct intervisibility. They are, thus, especially in complex environments of evolutionarily adaptive value. Despite this fact, vocal communication of the four great ape species, with some exceptions in chimpanzees, is barely investigated. Literature suggests that non-human primate vocalisations are inflexible and hardly controllable reflexes expressed involuntarily in emotional situations.
This project uses behaviour-observational methods to identify emotional contexts of the two different emotional valences, namely negative and positive emotional situations, that occur reliably in connection with certain vocalisations. There will be an acoustic analysis of the recorded vocalisations in order to investigate the exact acoustic structure and possible variations in slightly different contexts (references, social order, etc). Subsequently, experimental designs are used to ascertain the context specificity and functional use (e.g. flexibility, referentiality and/or intentionality) of the beforehand characterized vocalisations with special regard to possible differences between negatively and positively arousing interactions, proposing differences due to a phenomenon called negativity bias. The bias describes the propensity of a greater attention towards negative emotions due to their evolutionary urgency. It is, thus, less likely that the vocal expressions occuring in negative emotional contexts show great flexibility and controllability in contrast to positive vocalisations.
The experiments will be using a playback technique monitoring the behaviour of the apes in reaction to recorded vocalisations by hypothesising that the behaviour of the apes reflects the situation in which the vocalisation was recorded and so verifying its function.
Objects of research are vocal expresssions of orangutans. Orangutans are native to the Indonesian rain forests. Acoustic communication plays an essential role, particularly in the thick sylvan environment. But still, so far only little is known about the orangutan vocalisation behaviour, especially in emotional contexts. The major aim of this project is, thus, to get a deeper insight in the vocal communication behaviour of orangutans in emotionally arousing situations.
Prof. Dr. Katja Liebal