Abstract
From all non-human animals dogs are very likely the best decoders of human behavior. In addition to a high sensitivity to human attentive status and to ostensive cues, they are able to distinguish between individual human faces and even between human facial expressions. However, so far little is known about how they process human faces and to what extent this is influenced by experience. Here we present an eye-tracking study with dogs emanating from two different living environments and varying experience with humans: pet and lab dogs. The dogs were shown pictures of familiar and unfamiliar human faces expressing four different emotions. The results, extracted from several different eye-tracking measurements, revealed pronounced differences in the face processing of pet and lab dogs, thus indicating an influence of the amount of exposure to humans. In addition, there was some evidence for the influences of both, the familiarity and the emotional expression of the face, and strong evidence for a left gaze bias. These findings, together with recent evidence for the dog's ability to discriminate human facial expressions, indicate that dogs are sensitive to some emotions expressed in human faces.
Highlights
An important perceptual-cognitive challenge for almost all animals is to find a compromise between 'lumping and splitting' when confronted with the vast amount of information arriving at their senses [1]
The pet dogs looked longer at the negative compared to the positive emotions (F = 1,795.1 = 1.16, p = 0.28) whereas the lab dogs spent more time looking at the positive compared to the negative emotions (F1, 473.6 = 4.35, p = 0.04, see Fig 4)
Because lab dogs live in packs and are surrounded by other dogs but not humans, human faces are not salient enough to elicit a fast response
Summary
An important perceptual-cognitive challenge for almost all animals is to find a compromise between 'lumping and splitting' when confronted with the vast amount of information arriving at their senses [1]. The brain of many animals solves both tasks in a natural, effortless manner and with an efficiency that is difficult to reproduce in computational models and artificial systems. Still, how this is accomplished is far from being fully understood. An enormously rich source of information and an important category of visual stimuli for animals in all major vertebrate taxa is the face [2]. In many species faces convey, among other things, information about direction of attention, age, gender, attractiveness and current
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