How dogs scan familiar and inverted faces: an eye movement study
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Faces play an important role in communication and identity recognition in social animals. Domestic dogs often respond to human facial cues, but their face processing is weakly understood. In this study, facial inversion effect (deficits in face processing when the image is turned upside down) and responses to personal familiarity were tested using eye movement tracking. A total of 23 pet dogs and eight kennel dogs were compared to establish the effects of life experiences on their scanning behavior. All dogs preferred conspecific faces and showed great interest in the eye area, suggesting that they perceived images representing faces. Dogs fixated at the upright faces as long as the inverted faces, but the eye area of upright faces gathered longer total duration and greater relative fixation duration than the eye area of inverted stimuli, regardless of the species (dog or human) shown in the image. Personally, familiar faces and eyes attracted more fixations than the strange ones, suggesting that dogs are likely to recognize conspecific and human faces in photographs. The results imply that face scanning in dogs is guided not only by the physical properties of images, but also by semantic factors. In conclusion, in a free-viewing task, dogs seem to target their fixations at naturally salient and familiar items. Facial images were generally more attractive for pet dogs than kennel dogs, but living environment did not affect conspecific preference or inversion and familiarity responses, suggesting that the basic mechanisms of face processing in dogs could be hardwired or might develop under limited exposure.
KeywordsDomestic dog Eye movement tracking Face processing Face inversion effect Face familiarity
This study was financially supported by the Academy of Finland (project #137931 to O.Vainio and projects #129346 and #137511 to C.M. Krause) and Foundation of Emil Aaltonen. Special thanks to all pet dog owners for dedication to the training of dogs and providing photographs. We thank also Reeta Törne for assisting in the experiments and data preparation; Timo Murtonen for the custom-built calibration system and chin rests; Katja Irvankoski, Matti Pastell, Antti Flyck and Kristian Törnqvist for the technical support; and Mari Palviainen for the help in kennel dog training. The authors declare that they have no conflict of interest.
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