Does the odour of human stress or relaxation affect dogs’ cognitive bias?

Abstract Dogs can discriminate between stressed and non-stressed odour samples from humans, but the effect on their cognition and emotional state is previously unstudied. Eighteen dogs each participated in three cognitive bias sessions: baseline (no odour), stress odour and relax odour, with the order of the two test odours counterbalanced across dogs. The odours were combined breath and sweat samples from three volunteers showing measurable stress responses during a stress test compared to a relaxing activity. We found that dogs were significantly less likely to approach an ambiguous (near negative) location in the presence of stress odour. They were also significantly less likely to approach the trained unrewarded (negative) location and more likely to approach the rewarded (positive) location in the presence of both human odours. Learning over sessions and the order in which odours were presented also had significant effects, with the combination of stress odour and the last testing session having the greatest effect. This is the first study to show that in the absence of visual or auditory cues, olfactory cues of stress from an unfamiliar person may affect dogs’ cognition and learning. This could have important consequences for dog welfare and working performance.