The effects of strength and activation level of belief on belief-biased reasoning

The belief bias effect designates the tendency to judge the validity of a conclusion based on its believability. Most studies have compared highly believable with unbelievable conclusions when examining belief-biased reasoning. In two studies, we examine a hypothesis raised by Banks (2013, Cognitive Science, 37[3], 544-577), who postulated that level of activation of belief should affect the extent to which reasoning is biased. Here, a first study found that moderately believable conclusions produced a significant biasing effect, but one that was smaller than with highly believable conclusions. The second study found that activating the category referenced by a conclusion significantly increased the biasing effect of the same conclusion. These results suggest that strength of belief is a necessary parameter of any model of belief bias. They also show that context can affect the extent to which belief affects reasoning.