Positive and negative contexts predict duration of pig vocalisations

Abstract

Emotions are mental states occurring in response to external and internal stimuli and thus form an integral part of an animal’s behaviour. Emotions can be mapped in two dimensions based on their arousal and valence. Whilst good indicators of arousal exist, clear indicators of emotional valence, particularly positive valence, are still rare. However, positively valenced emotions may play a crucial role in social interactions in many species and thus, an understanding of how emotional valence is expressed is needed. Vocalisations are a potential indicator of emotional valence as they can reflect the internal state of the caller. We experimentally manipulated valence, using positive and negative cognitive bias trials, to quantify changes in pig vocalisations. We found that grunts were shorter in positive trials than in negative trials. Interestingly, we did not find differences in the other measured acoustic parameters between the positive and negative contexts as reported in previous studies. These differences in results suggest that acoustic parameters may differ in their sensitivity as indicators of emotial valence. However, it is important to understand how similar contexts are, in terms of their valence, to be able to fully understand how and when acoustic parameters reflect emotional states.

Piglets vocally express the anticipation of pseudo-social contexts in their grunts

“…The piglets expressed a similar frustration state during the anticipation phase as when the entrance of any (pseudo)social partner was delayed. We found an average duration for the phase of (0.31 < 0.35 < 0.39, table S4 ), value that are similar to what Briefer et al 19 found for negative contexts. This result is surprising because our behavioural data show that additional contact has a positive effect on the human-piglet relationship (Fig.…”

“…When the arrival of the partner was delayed, the duration of the piglets’ grunts increased for both partner types. Longer grunts had already been associated with a negative emotional valence 19 , 20 , 35 , which confirms that delaying the arrival of the partner led to a negative emotional state in comparison to the initial phase: a discrepancy from expectation that produced something like frustration. These results allow us to conclude that we did succeed in generating a specific anticipatory state during the tests which was expressed both behaviourally and vocally.…”

“…In a recent study, Briefer et al 19 showed that vocalisations (but not specifically grunts although they are usually over represented in datasets) recorded in positive contexts lasted 0.34 < 0.42 < 0.51 s. If we look at all of the grunts produced during the initial phase in our study, the average grunt duration is 0.13 < 0.27 < 0.41 s (Table S4 ). This may be in line with the first hypothesis, although the second hypothesis cannot be ruled out.…”

Piglets vocally express the anticipation of (pseudo)-social contexts in their grunts

“…When the arrival of the partner was delayed, the duration of grunts increased for both partner. Longer grunts had already been associated to negative emotional valence 18,19,28 , which confirms that the delay lead in piglets to a negative emotional state, a situation of non-correspondence with expectation, whatever the partner. These results allow us to conclude that we did succeed in generating a specific anticipatory state during the tests.…”

“…This latter phase is certainly a context with a negative valence (social isolation) and piglets may express the negative valence of this context in the duration of their grunt. In fact, several examples of the literature show that grunt duration is higher in negative contexts 18,28 . The duration of piglets’ grunt was not changed during anticipation.…”