The identification of facial expressions of emotions in dogs (Canis familiaris) using a Facial Action Coding System

Bremhorst, Annika (2021) The identification of facial expressions of emotions in dogs (Canis familiaris) using a Facial Action Coding System. PhD thesis, University of Lincoln.

The identification of facial expressions of emotions in dogs (Canis familiaris) using a Facial Action Coding System
PhD Thesis
Bremhorst, Annika - Life Sciences - November 2021.pdf - Whole Document

Item Type:Thesis (PhD)
Item Status:Live Archive


Objectively assessing animal emotions is challenging and requires the
development of valid and reliable indicators of emotions. Emotional states are
accompanied by behavioural expressions. If specific expressions reliably
accompany specific emotional states across contexts, then those expressions have
potential to serve as indicators of the emotional states. In human emotion research,
particularly facial expressions have been studied extensively for this purpose and
therefore may help infer animal emotions as well.
This project was aimed at studying facial expressions of dogs exposed to situations
that are likely to elicit positive anticipation and frustration. Both emotions can be
triggered in situations related to the expectation of a reward: while positive
anticipation can occur between signalling and delivery of a reward, it may turn into
frustration when the reward remains inaccessible. In a series of studies, using the
contingencies described, two contextual features were systematically varied – the
expected reward type (food/toys) and the social context (non-social/social; i.e.
whether the reinforcement was associated with a human or not). The main goal was
to identify facial expressions that are consistently associated with either positive
anticipation or frustration across contexts, as these expressions may serve as
indicators of the respective emotional states. To measure dogs’ facial expressions,
the Dog Facial Action Coding System (DogFACS) was used, which is the dog�specific adaptation of FACS, the gold standard for measuring facial expressions in
human emotion research.
Ears adductor was the only variable that was more common during positive
anticipation, and it was consistently associated with this state across (reward and
social) contexts. The antagonistic movement to the Ears adductor, Ears downward,
as well as Ears flattener and Nose lick were more common during frustration across
reward and social contexts. Despite the consistent association of those facial
expressions with positive anticipation or frustration, none of them would have
allowed consistent, correct designations of the associated emotional state when

used as individual indicators. Diagnostic accuracy assessments showed that validity
estimates of the Ears adductor varied greatly across contexts: whereas sensitivity
was low and specificity high in a non-social context, it was the other way round in a
social context. Similar to the Ears adductor, validity estimates of Ears downward
showed an inverse pattern between contexts: while in the non-social context Ears
downward was more sensitive than specific, this was the other way round in the
social context. Accuracy estimates of Ears flattener were more consistent, despite
some variation. Nose lick was the variable with the most stable accuracy measures
across contexts. On their own, these facial expressions would not serve as highly
reliable, robust, and valid indicators of positive anticipation or frustration in dogs.
However, they may be potential candidates for the future development of indicators
of these states, e.g. when combined with other facial or body expressions.
Additional facial expressions that were associated with frustration were Blink,
Tongue show, Lip corner puller, Jaw drop, and Lips part. However, although they
were not affected by the expected reward type, they only accompanied frustration
in a non-social context. Therefore, these facial expressions are less likely robust
candidates for the development of indicators of frustration in dogs. The Upper lip
raiser also accompanied frustration in non-social contexts, but it was influenced by
the expected reward type and may therefore be more related to the associated
motivational state.
The last study of this thesis focussed exclusively on the Inner brow raiser, which is a
facial expression that has received considerable attention related to its role in dog-human communication. When its production was compared between a social and a
non-social context, it occurred more frequently in the non-social context,
challenging the previous hypothesis of a communicative function. We also found
the Inner brow raiser to be strongly associated with eye movements, which suggests
a proximate mechanism behind this facial expression.
In this project, facial expressions, an infrequently studied modality in animal
(emotion) research, were identified that consistently accompanied either positive
anticipation or frustration across different (reward and social) contexts in dogs.

Although the Ears adductor was consistently associated with positive anticipation
and Ears downward, Ears flattener, and Nose lick with frustration, they do not seem
to constitute reliable, robust, and valid indicators of the respective emotions in their
own. Nonetheless, they are potential candidates that provide a starting point for the
future development of emotion indicators by systematically examining them in
combination with other expressive behaviours. The introduction of diagnostic
accuracy assessments is a pioneering approach to animal emotion research,
providing novel methods to advance the evaluation of the validity of putative
indicators of animal emotions.

Keywords:dog, facial expressions, FACS, dog-human communication
Subjects:D Veterinary Sciences, Agriculture and related subjects > D300 Animal Science
C Biological Sciences > C100 Biology
Divisions:College of Science > School of Life Sciences
ID Code:48503
Deposited On:09 Mar 2022 16:45

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