Spurious signal detection and delusions of reference in first-episode schizophrenia

Abstract

Background: Delusions of reference (DOR) are a group of highly prevalent psychotic symptoms. In DOR, patients experience attentional capture by certain otherwise neutral aspects in the environment, which were regarded as self-referential. Theoretically, aberrant salience as a result of excessive dopamine firing may lead to spurious signal detection in patients with DOR. We test the hypothesis that patients presenting with and DOR have increased false alarms in a visual and an auditory signal detection task, compared with patients not experiencing the symptom and with healthy controls. Methods: A total of 32 patients with first-episode schizophrenia (mean age 24.3±6.9 years, 19 men) and 17 healthy controls (mean age 24.7±7.7 years, 9 men) were recruited. Controls and patients were matched in age, sex and education. Patients were further divided into a DOR group (n=15) and a non-DOR group (n=17). DOR was assessed using the Ideas of Reference Interview Scale (IRIS). Spurious signal detection was tested using the randomized and sequential Contour Integration Test (Field, Hayes, and Hess 1993) for visual processing and the Babble Task (Hoffman et al, 2007) for auditory processing. Performance was compared between groups using ANOVA and post-Hoc analysis. Signal detection analyses were carried out to differentiate between genuine spurious signal detection and response bias. Relationship between IRIS scores and false alarm rates was explored. Results: Spurious signal detection was observed in both DOR groups and healthy controls in low signal-to-noise trials. In the Contour Integration Test, patients with DOR were more likely to detect spurious signals particularly when the stimuli were presented at a moderate signaltonoise ratio compared with the other two groups (p<0.01), with an effect size of 1.11 (Cohen’s d). False alarms are correlated with DOR severity (r=0.39, p<0.01). All three groups demonstrated good sensitivity and conservative response in signal detection. A similar trend was seen in the Babble Task. Discussion: Spurious signal detection is a common phenomenon under noisy conditions, which can be elicited also in healthy subjects. In DOR, there appears to be increased spurious signal detection, at a moderate signal-to-noise ratio. This observation cannot be accounted for by a general decline in task performance or a more liberal response bias, suggesting genuine false detection of signals in patients with DOR. This study provided initial findings for further investigation into the neurocognitive substrates of DOR.