Abstract
Dogs process faces and emotional expressions much like humans, but the time windows important for face processing in dogs are largely unknown. By combining our non-invasive electroencephalography (EEG) protocol on dogs with machine-learning algorithms, we show category-specific dog brain responses to pictures of human and dog facial expressions, objects, and phase-scrambled faces. We trained a support vector machine classifier with spatiotemporal EEG data to discriminate between responses to pairs of images. The classification accuracy was highest for humans or dogs vs. scrambled images, with most informative time intervals of 100–140 ms and 240–280 ms. We also detected a response sensitive to threatening dog faces at 30–40 ms; generally, responses differentiating emotional expressions were found at 130–170 ms, and differentiation of faces from objects occurred at 120–130 ms. The cortical sources underlying the highest-amplitude EEG signals were localized to the dog visual cortex.
Highlights
Dogs process faces and emotional expressions much like humans, but the time windows important for face processing in dogs are largely unknown
We showed images of pleasant, threatening and neutral dog and human facial expressions as well as objects and phase-scrambled images to eight dogs that were previously trained with positive operant conditioning to undergo the EEG measurement procedures
It adds to our understanding of the surrounding biological diversity and answers to our curiosity of the non-human minds—in this case, how does a dog see and process the social world? Second, it contributes to our views of the uniqueness of humans
Summary
Dogs process faces and emotional expressions much like humans, but the time windows important for face processing in dogs are largely unknown. By combining our non-invasive electroencephalography (EEG) protocol on dogs with machine-learning algorithms, we show category-specific dog brain responses to pictures of human and dog facial expressions, objects, and phase-scrambled faces. Dogs perform rather well in object recognition tasks They are able to visually distinguish faces from non-faces, observing them spontaneously differently[4,5] and they view faces in a holistic manner like humans, differentiating upright from inverted faces[6,7]. Dog fMRI studies have shown differentiation in canine processing of human and dog faces[19] and between different emotional expressions[20]. Our previous study was more of a feasibility test and not optimized for comparing different categories of objects
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