Measuring judgement bias in non-human animals – could a new, body size awareness-based paradigm be the practical answer?

Inner states of non-verbal animals remain elusive to assess. The principle of cognitive bias relies on the effect of inner states on decision-making. In a judgement bias test, the subject decides whether an ambiguous stimulus resembles more a previously learnt non-rewarding or rewarding stimulus. Unfortunately, these testing protocols incorporate lengthy training procedures and arbitrary stimuli. We propose a new approach that is based on the dogs’ natural behaviour, the ability to manoeuvre in the physical world. In our new, body size representation-based method, we offered dogs (N=42) either a comfortably large, a too small, or a medium-sized (ambiguous) door to get to the reward, where the subjects’ decision was dependent on their knowledge about their body size. Additionally, dog owners completed a questionnaire about the dogs’ responses to potentially stressful situations. After an initial introduction to the test area (warm-up phase), dogs went through a familiarisation phase in the first 10 trials, followed by a test phase in trials 11-13. In trials 1-12, either a large enough or a too small opening was offered and in trial 13, the ambiguous stimulus was a medium-sized opening. We found that dogs with lower ‘Relaxed’ questionnaire component score approached the medium-sized door sooner than dogs with high 'Relaxed’ scores. The new judgement bias test represents a viable option for assessing dogs’ affective states. However, the interpretation of the subjects’ responses should be based on the testing method. Using an ecologically valid paradigm has several advantages, but most importantly, it shortens the training phase that other judgement bias tests require. Our new method can be important for clinicians and professionals, as these tests are often used to assess the well-being of captive animals. • We describe a new body-size awareness test to assess dogs' affective state • Dogs judged an ambiguous opening based on their own body-size knowledge • Less relaxed dogs approached the ambiguous stimulus faster • The method avoids arbitrary stimuli and lengthy training in judgement bias tests