The experience was not easy to perform, but it was done! Psychologists have shown that rats were also subject to the conjunction error, one of the most famous cognitive biases that distort our reasoning.
Hervé Poirier, editor-in-chief at the magazine Epsiloon, explains to us today that rats are also subject to the “conjunction error”, a cognitive bias that was thought to be specific to human reasoning. The cognitive mechanisms underlying these biases were thought to be unique to our brains. But no: this experience demonstrates the universality of our way of thinking.
franceinfo: Is this the first time that such a bias has been highlighted in non-humans?
Herve Poirier: The conjunction error was highlighted by the psychologists Tversky and Kahneman in 83, with the famous “Linda problem”. If I tell you that a certain Linda is 31 years old. Single, frank, brilliant, she has a master’s degree in philosophy, is concerned about issues of discrimination and social justice, she has participated in anti-nuclear demonstrations. In your opinion, is Linda more likely to be: a teller in a bank or a teller in a bank and active in the feminist movement?
The second answer?
Well you have fallen into the trap. 90% of humans answer this way. Which is not logical: even if the elements suggest it, it is not 100% sure that Linda is today a committed feminist. She is therefore more likely to be just a banker, rather than a banker and a feminist. More generally, the conjunction of two events cannot be more probable than the occurrence of each of them, taken in isolation. Well, psychologists have just shown that rats, too, are subject to this “conjunction error”.
How did they do it?
They adapted Linda’s problem, through very subtle tests, involving sounds, lights and rewards. Overall, the behavior of the rats shows that they tend to think that the event “the light is on” is less likely than the event “the light is on and a sound is heard”. Another conjunction error. And this is the first time that this type of cognitive bias has been highlighted in non-human thought.
How to interpret this?
It’s actually not that surprising. Confirmation bias, anchoring bias, retrospective bias, psychologists have spotted dozens of them that undermine our rationality. These biases certainly lead to errors, but speed up decision-making, most often in a relevant way: a key driver for survival. And it is therefore a safe bet that rats, but also kangaroos or giraffes, are subject to these same systematic deviations from rational thought. On Earth, no brain is wired to be logical.