19/07/2026
Judgement Bias in Dogs: Why Some Dogs Always Think the Worst 👇
Why do two dogs react so differently to exactly the same situation?
Imagine two dogs hear an unexpected noise behind a fence. One pauses for a moment before carrying on. The other immediately barks, retreats or scans the environment, convinced something isn’t right.
The difference isn’t obedience and might not even be previous training.
It may be something behavioural scientists call judgement bias.
What is judgement bias?
Judgement bias describes how an individual interprets ambiguous information.
When neither we nor our dogs have enough information to know what will happen next, the brain makes a prediction.
Will this turn out well?
Or should I prepare for something unpleasant?
Some dogs tend to interpret uncertainty optimistically and expect good outcomes. Others are more likely to think the worst, assuming that something unfamiliar could signal danger. These expectations influence the decisions they make long before we see any obvious behaviour.
Scientists can actually measure optimism
One of the most fascinating discoveries in canine cognition is that researchers have developed ways of measuring optimism and pessimism in dogs.
In a landmark study, dogs were taught that a bowl placed in one location always contained food, while a bowl in another location was always empty. Once they understood the pattern, researchers placed bowls in ambiguous locations between the two.
Dogs showing separation-related behaviour approached these uncertain bowls more slowly than control dogs, suggesting they expected a less favourable outcome. In other words, their emotional state influenced how they interpreted uncertainty—not just how they behaved when left alone (Mendl et al., 2010).
This was one of the first demonstrations that dogs, like humans, can display measurable cognitive biases.
Behaviour is often driven by prediction
Understanding judgement bias changes the questions we ask.
Instead of asking:
“Why is this dog barking?”
We might ask:
“What does this dog think is about to happen?”
That simple shift changes everything.
A dog barking at an unfamiliar person may not be trying to dominate or intimidate. They may simply think the worst. If their brain predicts that the unfamiliar person could pose a threat, creating distance suddenly becomes a very logical strategy.
Likewise, a dog who hesitates around a novel object may simply have learned that uncertainty often leads to unpleasant experiences.
Behaviour makes far more sense when we understand the drivers underneath it.
Can judgement bias change?
Perhaps the most encouraging finding is that judgement bias is not fixed.
Research by Karagiannis and colleagues (2015) found that dogs receiving treatment for separation-related behaviour became progressively less pessimistic during judgement-bias testing.
Importantly, the researchers weren’t simply seeing fewer problem behaviours. The dogs appeared to interpret ambiguous situations more positively than they had before treatment.
This suggests that successful behaviour modification may do more than change what a dog does.
It may change how the dog navigates the whole world.
What does this mean for behaviour professionals?
When we understand judgement bias, we stop seeing behaviour as isolated reactions and start recognising it as part of a dog’s decision-making process.
Our role becomes helping dogs build a history of predictable, safe and positive experiences. By reducing unnecessary ambiguity, giving dogs appropriate choice and control, and carefully creating successful learning opportunities, we can help shift their expectations about the world around them.
Because behaviour isn’t simply about changing actions.
Sometimes it’s about changing the predictions that create those actions.
References
Karagiannis, C. I., Burman, O. H. P., & Mills, D. S. (2015). Dogs with separation-related problems show a less pessimistic cognitive bias during treatment with fluoxetine. Journal of Veterinary Behavior, 10(6), 543–547.
Mendl, M., Brooks, J., Basse, C., Burman, O. H. P., Paul, E. S., Blackwell, E. J., & Casey, R. A. (2010). Dogs showing separation-related behaviour exhibit a “pessimistic” cognitive bias. Current Biology, 20(19), R839–R840.
Starling, M. J., Branson, N., Cody, D., & McGreevy, P. D. (2014). Canine Sense and Sensibility: Tipping Points and Response Latency Variability as an Optimism Index in a Canine Judgement Bias Assessment. PLoS ONE, 9(9), e107794.
