New research from the University of California, Los Angeles (UCLA) has uncovered an intriguing connection between humans and rats: both species appear to fall victim to the same type of logical fallacy, known as the conjunction fallacy. This groundbreaking study, published in the journal Psychonomic Bulletin and Review, suggests that the underlying cognitive mechanisms behind this fallacy may be shared across species, opening up the possibility of using rats as research models for studying certain psychopathological conditions.
The conjunction fallacy is a well-documented psychological phenomenon, famously exemplified by the “Linda problem” designed by Nobel laureate Daniel Kahneman and his colleague Amos Tversky in the 1980s. They presented participants with a scenario describing a woman named Linda, who is highly educated, socially conscious, and politically active. Participants were then asked to decide whether it was more probable that Linda was a bank teller, or a bank teller active in the feminist movement. Most chose the latter option, despite the fact that it is logically less probable.
This error in reasoning is thought to arise from the use of mental shortcuts, or heuristics, when estimating the likelihood of an event. In the case of the Linda problem, participants may have relied on the representativeness heuristic, assessing how similar the event is to a mental model they already have in their minds. This cognitive process, believed to be unique to humans, involves a combination of memory, imagination, and reasoning.
However, the recent study from UCLA challenges the idea that the conjunction fallacy is exclusive to humans. Valeria González, a postdoctoral psychology researcher at UCLA and the study’s first author, explains: “The classical research has all been done with humans, so the usual explanation for the effect attributes it to a departure from rationality distinct to humans. Our work shows that maybe there is a more general mechanism shared between humans and rats.”
The discovery that rats, like humans, are susceptible to the conjunction fallacy has significant implications for the field of psychology. If rats indeed share this cognitive bias with humans, they could potentially serve as useful models for studying psychopathological conditions characterized by false beliefs or the perception of nonexistent events, such as schizophrenia and certain anxiety disorders.
The conjunction fallacy occurs when people believe that the combination of two events is more likely than just one of those events occurring. Some researchers have argued that this fallacy arises due to language, particularly people’s uncertainty about the meaning of words like “likely” and “probability.” Others have attributed the fallacy to the influence of detailed backstories on decision-making. Additionally, previous research has indicated that humans are prone to conjunction fallacies when performing physical tasks.
To investigate whether the fallacy is necessarily tied to language and whether it is unique to humans, González and psychology professor Aaron Blaisdell designed an experiment involving rats in a physical, rather than social, task. The rats were trained in two scenarios where they had to judge the likelihood of a sound being present or both a light and sound being present in order to receive a food reward.
In the first scenario, the rats received sugar pellets if they pressed a lever when a tone played and a steady light was on. If the tone played but the light was off, they received no food. In the second scenario, the rats received pellets if they pressed a lever while a white noise played and a flashing light was off. However, they received nothing if they pressed the lever when the noise played and the flashing light was on.
The researchers then played the different sounds, a tone or white noise, with the light bulb unobscured but turned off. The rats reacted accordingly, tending to avoid pressing the lever in response to the tone and pressing it in response to the white noise. However, when the researchers obscured the light bulb with a piece of metal and played the sounds, the rats were forced to predict whether the light was on or off in hopes of receiving the food reward.
Interestingly, the rats were much more likely to predict that the obscured light was on, regardless of whether the light had previously signaled the presence or absence of food when accompanying the sound. This tendency to overestimate the likelihood that both sound and light were present, even if it meant no reward, demonstrates that rats, like humans, can exhibit the conjunction fallacy.
“Until now, researchers said this is unique to human cognition only because we haven’t looked for it in animals,” Blaisdell said. “If humans and other animals consider alternative states of the world during ambiguous situations to help decision-making, we might expect systematic biases such as the conjunction fallacy to show a broader distribution in the animal kingdom.”
By demonstrating that the conjunction fallacy is not solely the province of humans, the UCLA researchers have opened up new avenues for investigation and potential treatments for these disorders. Furthermore, this study serves as a reminder that even in the realm of cognitive biases and heuristics, humans may not be as unique as previously thought.
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