Logic, intuition and delusions: dual stream processing biases in decision-making

Delusions, a key characteristic of schizophrenia, are fixed false beliefs that are firmly held despite convincing evidence to the contrary. An underlying mechanism that can account for this debilitating symptom remains elusive. “Dual-stream information processing” is a decision-making model that divides reasoning into two separate components: a fast, intuitive stream, and a slower, logical stream, similar to our understanding of decisions made by the “”heart”” or “”gut”” versus those made by the “”head””. For most decisions, intuition and logical reasoning converge onto the same conclusion. However, in instances where intuition and reason do not agree, there may be processing differences between healthy people and people with schizophrenia. Healthy people show a bias toward the logical stream, prompting them to more carefully examine the available evidence. In schizophrenia, individuals may not detect conflict between the two streams and may not have a bias toward the logical conclusion. This could enable their erroneous intuitive interpretations of events to endure unchallenged, leading to delusions. William Speechley is testing this hypothesis by studying how people make sense of conflicts between the intuitive and logical streams of reasoning. Healthy individuals and delusional schizophrenia patients will be given reasoning tasks and their brain activity will be recorded using functional magnetic resonance imaging (fMRI). He predicts that healthy controls and delusional schizophrenia patients will differ when the two streams of reasoning conflict, and that the patient group will not adequately recruit logical reasoning areas of the brain during conflict. He also expects that fMRI will indicate greater activity in areas relating to intuitive processing among schizophrenics. This research will make a significant contribution to our understanding of the cognitive basis for the formation and maintenance of delusions in schizophrenia, potentially leading to more effective treatment strategies.