Cognitive Bias and Affective States in Non-Human Animals

Cognitive bias in non-human animals refers to systematic shifts in information processing that reflect an individual’s affective state. Such biases manifest when animals interpret ambiguous cues as more positive (optimistic bias) or negative (pessimistic bias), offering an indirect window onto their emotional lives. Over the past decade, a range of taxa—from invertebrates through to mammals—has been shown to exhibit judgement biases following experimental manipulations of stress, reward or environmental conditions. Tasks commonly involve training animals to discriminate between positive and negative outcomes and then probing their responses to intermediate stimuli. Evidence now links cognitive biases to welfare, personality and adaptive foraging or defensive strategies. Practical applications span welfare assessment in farm and companion animals, refinement of conservation practices and models of human affective disorders. Integrating behavioural assays with neurobiological and computational approaches has begun to reveal the mechanisms by which mood‐like and emotion‐like states influence decision making, underscoring the evolutionary continuity of affective cognition.

Research from Nature Portfolio

Studies in dogs demonstrate that olfactory cues of human stress can induce a pessimistic judgement bias in the absence of visual or auditory signals. When exposed to odours collected during human stress, dogs were less likely to approach an ambiguously located food bowl, indicating lowered expectations of reward and altered learning trajectories. In dairy calves, individual differences in judgement bias were shown to be stable over time and to correlate with fearfulness, suggesting that personality traits shape optimistic or pessimistic tendencies under ambiguity. Research in young chickens reveals that environmental complexity can buffer against stress‐induced negative biases: enriched rearing conditions preserved optimistic responses to ambiguous cues even after unpredictable stressors, and mesencephalic dopamine turnover was positively associated with optimistic bias. These findings highlight the interplay between external context, neurochemistry and cognitive evaluations of uncertain outcomes.

Cognitive Bias and Affective States in Non-Human Animals publication trend

The graph below shows the total number of articles in cognitive bias and affective states in non-human animals across all publications each year (not limited to Nature Index journals).

Technical terms

Cognitive bias: A systematic deviation in information processing reflecting underlying emotional states.

Affective state: The current emotional or mood-like condition of an animal, influencing cognition and behaviour.

Judgement bias test: An experimental paradigm assessing optimism or pessimism through responses to ambiguous cues.

Ambiguous stimulus: A cue intermediate between trained positive and negative signals, used to probe expectation biases.

Pessimistic bias: A tendency to interpret ambiguous information as predicting negative outcomes.

Optimistic bias: A tendency to interpret ambiguous information as predicting positive outcomes.

References

1. Fearful snake pictures make monkeys pessimistic. iScience (2023).
2. The odour of an unfamiliar stressed or relaxed person affects dogs’ responses to a cognitive bias test. Scientific Reports (2024).
3. Physically stressed bees expect less reward in an active choice judgement bias test. Proceedings of the Royal Society B (2024).
4. Making Decisions under Ambiguity: Judgment Bias Tasks for Assessing Emotional State in Animals. Frontiers in Behavioral Neuroscience (2016).
5. Animal affect and decision-making. Neuroscience & Biobehavioral Reviews (2020).
6. Laughing Rats Are Optimistic. PLOS ONE (2012).
7. Pessimism and fearfulness in dairy calves. Scientific Reports (2018).
8. Environmental complexity buffers against stress-induced negative judgement bias in female chickens. Scientific Reports (2018).