A judgement bias task: implications for our understanding of emotional lateralisation in chicks (G. gallus domesticus)

The field of animal cognition has shown increasing interest in the development of reliable ways to assess animals’ emotional states. Cognitive biases, including judgement biases, seem to be a promising solution, as they allow to assess the animal’s emotional state through observable and quantifiable behaviour. In this experimental study, we investigated the effects of a positive or a negative emotional treatment on 3-day-old domestic chicks (G. gallus domesticus; n=92, 46 in the positive treatment condition and 46 in the negative treatment condition). After having tested chicks’ motivation, we observed their approach behaviour towards familiar stimuli before the emotional treatment and towards an ambiguous one after it. Emotional treatments involved either affiliative or distress-inducing conditions. We expected the emotional treatment to influence how they would interpret the ambiguous stimulus. To examine potential lateralised brain activation associated with affect, chicks were simultaneously presented with the same stimulus on the right and left of their visual fields, and their approach behaviour towards both was analysed. Behavioural data were recorded and analysed using ANOVA. Results revealed consistent differences in latencies and in approach behaviour between pre- and post-treatment conditions, indicating that the treatment was potentially effective in inducing a positive or negative emotional state, determining a judgment bias. However, the absence of significant differences in some behavioural indexes and a lack of discrimination between high- and low-value stimuli raise questions about training efficacy and treatment validity. Notably, no effect was observed on chicks’ behaviour in terms of side preferences depending on the treatment and on their emotional state. Possible explanations for these results are presented, along with suggestions for future research.