Emotional facial expressions are an important part of across species social communication, yet the factors affecting human recognition of dog emotions have received limited attention. Here, we characterize the recognition and evaluation of dog and human emotional facial expressions by 4-and 6-year-old children and adult participants, as well as the effect of dog experience in emotion recognition. Participants rated the happiness, anger, valence, and arousal from happy, aggressive, and neutral facial images of dogs and humans. Both respondent age and experience influenced the dog emotion recognition and ratings. Aggressive dog faces were rated more often correctly by adults than 4-year-olds regardless of dog experience, whereas the 6-year-olds’ and adults’ performances did not differ. Happy human and dog expressions were recognized equally by all groups. Children rated aggressive dogs as more positive and lower in arousal than adults, and participants without dog experience rated aggressive dogs as more positive than those with dog experience. Children also rated aggressive dogs as more positive and lower in arousal than aggressive humans. The results confirm that recognition of dog emotions, especially aggression, increases with age, which can be related to general dog experience and brain structure maturation involved in facial emotion recognition.
Introduction
Interpreting emotions from facial expressions is an important part of nonverbal social communication across species and lifespan [1–3]. Already Darwin [4] claimed that emotions are expressed by all species and that humans can determine other animals’ emotions from their facial and bodily expressions [but see also 5]. Several brain areas have been found to be involved in the processing of facial emotions, but studies are still lacking consensus and there has been variability in study results [6, 7]. Multiple variables can impact to the recognition of facial expressions, for example respondent’s gender and partially occluding the face area [8, 9]. Humans are experts in recognizing another person’s emotions by observing facial expressions [e.g., 10–12], but humans’ ability to recognize dog emotional expressions has been studied less [13]. Only a few studies have investigated the ability of young children to recognize and evaluate dogs’ facial expressions or made comparisons between the abilities of children and adults [14–16]. Previous studies suggest that young children lack abilities to interpret emotional expressions of dogs, which deserve more detailed attention in order to improve the quality and understanding of the real-life interactions between children and dogs.
Previously, dog owners’ attribution of emotions to their dogs have been commonly investigated by rating discrete emotions, such as happiness and aggressiveness [17, 18]. However, little research has used valence and arousal ratings of dog emotions based on two-dimensional approach, where emotions can be described using negative/positive valence dimension and low/high arousal dimension [19–21]. To our knowledge, this is one of the first studies, where valence and arousal ratings were combined with rating of discrete emotion to assess children’s abilities to interpret dog emotions from facial expressions [see also 15].
In previous studies, the human evaluation of dog emotional signals has been investigated with auditory dog bark playback stimuli [22, 23], with audio-visual dog vocalization and behavior recordings [16, 24], with dog facial images [13, 14, 25] and/or full body videos of dogs [15, 26–29]. Long-shared history and the special human-dog bond may have led both humans and dogs to develop skills to understand each other’s emotional expressions [e.g., 13, 22, 30–33]. According to previous studies, pleasant and threatening dog facial expressions are classified in a similar manner as human facial expressions [25, 34]. However, all emotions are not expressed alike across species, and for humans, some dog emotions might be easier to recognize than others. For example, dogs’ playful/happy expressions appear easier to recognize than aggressiveness or fear [13, 35–37].
Also, the effect of human everyday experience with dogs (e.g., having a dog in the family) in recognizing dog emotions is still unclear. Co-domestication hypothesis suggests that humans have the ability to read dog emotions through emotionally adapted mechanisms, meaning that these skills should be partially present also without dog experience [e.g., 38, 39, but see 35]. In some of the previous experiments, humans without dog experience have been as good as humans with dog experience in recognizing dog emotions from auditory or visual cues [22, 34] or sometimes even better [13, 28], whereas in other experiments, dog experience has improved dog emotion recognition especially in adults [14, 40]. Additionally, dog expertise was also found to affect both neural processing of and visual attention to dog social interaction in adult observers in a brain imaging study [41]. As expertise effects in interpretation of dogs has been found in a number of studies, it is thus also possible that dog experience influences perception and recognition of dog emotional expressions as emotion recognition is an important part of social communication. One explanation for the apparent controversy of the previous results is differing levels of experience (from having a dog in the family to experienced dog trainer) used in different experiments, together with other possible affecting factors such as different types of stimuli used (e.g., visual, auditory or both). Therefore, more research is needed to disentangle the possibly multiple concurrent sources of the factors affecting the human perception of canine emotions.
Facial expressions of emotions are processed in a large network of brain areas including prefrontal cortices, the fusiform gyrus, insula, and the amygdala among others [e.g., 42–47]. Studies suggest that these brain structures continue to mature throughout late childhood to adolescence, and that recognition of facial emotions may not reach maturity before adult age [e.g., 3, 48, 49]. Also, Theory of Mind (ToM), which is the ability to ascribe mental states to others, continues to develop beyond preschool years [50; for a review e.g., 51, 52]. A previous study showed that 4–5-year-old children have limited ability to understand dog bodily signals compared to 6–12-year-old children [16]. Limited ability in reading dogs’ body postures and facial expressions can lead into dangerous situations [e.g., 29, 53]. For example, children may assume that a dog with exposed teeth is smiling although the expression is a serious warning signal to keep distance [e.g., 16, 54]. Another study reported that 5–6-year-old children were less adept than adults at reading dog emotions, except for anger and happiness that were also recognized by children [14]. Thus, the literature suggests effects of human developmental stage in the evaluation of dog emotional expressions, but the time courses of development and exact effects appear somewhat unclear.
Here, we investigated how different dog and human emotional expressions are recognized and evaluated by 4-and 6-year-old children and adults. These age groups were selected on the basis of previous literature: 3–5-year-old children have shown limited ability to read dogs’ emotions compared to older children and adults [e.g., 16, 24, 36]. We also wanted to further characterize the effect of daily dog experience, or exposure (i.e., whether there has been dog in the family) in recognizing dog expressions, henceforth referred as “dog experience”. The first aim of this study was to evaluate the effect of age on the emotion detection, and also quantify whether the age has an effect on valence and arousal ratings. Based on previous studies [e.g., 15, 16, 29], we expected that the performance of 4-year-olds, 6-year-olds and adults differ from each other. The second aim was to assess the effect of daily dog experience on dog emotion recognition. Based on previous studies [14, 40], we assumed that dog experience has an effect especially on adults’ performance, because of their cumulative experience with dogs. The third aim was to clarify how children and adults recognize and rate affect in dog facial expressions compared to human expressions. In previous literature, negative and positive expressions in humans and dogs have been processed quite similarly by children and adults [14, 25, 34], but also some differences have been found in the ability of children to recognize dog emotions compared to human emotions [14, 15].