Abstract
Delusions are defined as fixed erroneous beliefs that are based on misinterpretation of events or perception, and cannot be corrected by argumentation to the opposite. Cognitive theories of delusions regard this symptom as resulting from specific distorted thinking styles that lead to biased integration and interpretation of perceived stimuli (i.e., reasoning biases). In previous studies, we were able to show that one of these reasoning biases, overconfidence in errors, can be modulated by drugs that act on the dopamine system, a major neurotransmitter system implicated in the pathogenesis of delusions and other psychotic symptoms. Another processing domain suggested to involve the dopamine system and to be abnormal in psychotic disorders is sensory perception. The present study aimed to investigate whether (lower-order) sensory perception and (higher-order) overconfidence in errors are similarly affected by dopaminergic modulation in healthy subjects. Thirty-four healthy individuals were assessed upon administration of l-dopa, placebo, or haloperidol within a randomized, double-blind, cross-over design. Variables of interest were hits and false alarms in an illusory perception paradigm requiring speeded detection of pictures over a noisy background, and subjective confidence ratings for correct and incorrect responses. There was a significant linear increase of false alarm rates from haloperidol to placebo to l-dopa, whereas hit rates were not affected by dopaminergic manipulation. As hypothesized, confidence in error responses was significantly higher with l-dopa compared to placebo. Moreover, confidence in erroneous responses significantly correlated with false alarm rates. These findings suggest that overconfidence in errors and aberrant sensory processing might be both interdependent and related to dopaminergic transmission abnormalities in patients with psychosis.
Highlights
It has long been proposed that conscious perception is not the mere result of sensory stimulation, but reflects an interaction between sensation and previous experience (Von Helmholtz, 1867)
Based on the role of dopaminergic transmission in perceptual processes, it has been suggested that an excess of dopamine leads to aberrant stimulus salience by affecting (a) the signal-tonoise ratio of sensory processing, such that noise is perceived as a meaningful signal (Corlett et al, 2010); and/or (b) the prediction error signal, such that neutral or innocuous stimuli are perceived as bearing significance (Kapur, 2003)
As delusions are thought to result from abnormally increased dopaminergic activity, we investigated the effect of dopaminergic manipulation on delusionassociated reasoning biases
Summary
It has long been proposed that conscious perception is not the mere result of sensory stimulation, but reflects an interaction between sensation and previous experience (Von Helmholtz, 1867). Delusions are regarded as resulting from specific disruptions in the normal processes for belief generation and evaluation (Langdon et al, 2010) Such ‘metacognitive’ disruptions, subsumed under the term ‘reasoning biases,’ correspond to thinking styles that lead to a distorted integration and interpretation of perceived stimuli (Bell et al, 2006; Freeman, 2007). Several such biases have been consistently shown to be associated with delusions, such as jumping-to-conclusions (i.e., a tendency to draw inferences based on limited evidence; Garety and Freeman, 2013), increased confidence in false judgments (Moritz et al, 2008), and a bias against disconfirmatory evidence (Woodward et al, 2006). It was further expected that detection performance would be significantly correlated with error overconfidence
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