Reasoning heuristics across the psychosis continuum: The contribution of hypersalient evidence-hypothesis matches

Introduction. Hypersalience of evidence-hypothesis matches has recently been proposed as the cognitive mechanism responsible for the cognitive biases which, in turn, may contribute to the formation and maintenance of delusions. However, the construct lacks empirical support. The current paper investigates the possibility that individuals with delusions are hypersalient to evidence-hypothesis matches using a series of cognitive tasks designed to elicit the representativeness and availability reasoning heuristics. It was hypothesised that hypersalience of evidence-hypothesis matches may increase a person's propensity to rely on judgements of representativeness (i.e., when the probability of an outcome is based on its similarity with its parent population) and availability (i.e., estimates of frequency based on the ease with which relevant events come to mind). Methods. A total of 75 participants ( 25 diagnosed with schizophrenia with a history of delusions; 25 nonclinical delusion-prone; 25 nondelusion-prone controls) completed four heuristics tasks based on the original Tversky and Kahnemann experiments. These included two representativeness tasks ("coin-toss'' random sequence task; "lawyer-engineer'' base-rates task) and two availability tasks ("famous-names'' and "letter-frequency'' tasks). Results. The results across these four heuristics tasks showed that participants with schizophrenia were more susceptible than nonclinical groups to both the representativeness and availability reasoning heuristics. Conclusions. These results suggest that delusional ideation is linked to a hypersalience of evidence-hypothesis matches. The theoretical implications of this cognitive mechanism on the formation and maintenance of delusions are discussed.