Abstract
During social interactions, acoustic parameters of tetrapods’ vocalisations reflect the emotional state of the caller. Higher levels of spectral noise and the occurrence of irregularities (non-linear phenomena NLP) might be negative arousal indicators in alarm calls, although less is known about other distress vocalisations. Family dogs experience different levels of stress during separation from their owner and may vocalise extensively. Analysing their whines can provide evidence for the relationship between arousal and NLP. We recorded 167 family dogs’ separation behaviour including vocalisations, assessed their stress level based on behaviour and tested how these, their individual features, and owner reported separation-related problems (SRP) relate to their whines’ (N = 4086) spectral noise and NLP. Dogs with SRP produced NLP whines more likely. More active dogs and dogs that tried to escape produced noisier whines. Older dogs’ whines were more harmonic than younger ones’, but they also showed a higher NLP ratio. Our results show that vocal harshness and NLP are associated with arousal in contact calls, and thus might function as stress indicators. The higher occurrence of NLP in older dogs irrespective to separation stress suggests loss in precise neural control of the larynx, and hence can be a potential ageing indicator.
Highlights
During social interactions, acoustic parameters of tetrapods’ vocalisations reflect the emotional state of the caller
The arousal and valence state of an individual affects the muscles participating in vocal production, resulting in different tension states of the vocal folds and the muscles involved in sound production leading to specific vocal structure, through which listeners are able to assess the emotional state of the caller
Different types of non-linear phenomena (NLP) can be found in v ocalisations[6,8,9] (Fig. 1), such as the appearance of quasiperiodic vibrations called subharmonics when the vocal folds start to move with different frequencies
Summary
Acoustic parameters of tetrapods’ vocalisations reflect the emotional state of the caller. When trying to explain the link between inner states and the acoustic features of vocalisations, Morton formulated his motivational–structural rules based on morphological effects on call structure[1] He suggested that size constrains, causing larger individuals to have lower pitch and smaller ones higher through a ritualization process, which led to the association between dominance and low pitch and submission with high pitch. Biphonation can occur when two independent (e.g. an additional source in the vocal tract10) or seemingly independent (e.g. vocal lips on the vocal folds11) sound sources function in parallel producing two fundamental frequencies (f0 and g0) during vocalisation, or due to the modulation of the fundamental frequency (f0) by lower frequency vibrations[12] These phenomena can be differentiated from subharmonics due to the fact that the ratio between the two pitches is not a fraction of integers. While a few studies have collected data supporting the adaptive functions of NLP in alarm calls (e.g. unpredictability:[14,15]; arousal:16) little is known about other distress vocalisations
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