An Investigation of Mechanisms That Underly Paranoia in Behaviour and Brain That Can Inform Clinical Diagnoses That Include Paranoid Symptoms.

participants are engaging in a set of tasks that measure inference and decision making. Outcome measures are estimated using a computational model that takes other aspects of the task and decision making into account as is custom in computational modeling of behaviour in cognitive psychology and computational psychiatry.

Hopkins verbal learning task - Revised (HVLT-R) is a part of the MATRICS Consensus Cognitive Battery (PAR, Inc FL 33549). The first phase of the test is an immediate recall phase where participants are read a list of 12 words across three trials (nouns from three taxonomic categories) and participants have to recall the words immediately after. There are 5 validated versions of the HVLT-R and the order of test versions will be randomised for each participant to prevent potential order effects. The more words recalled the higher the score.

Hopkins verbal learning task - Revised (HVLT-R) is a part of the MATRICS Consensus Cognitive Battery (PAR, Inc FL 33549). It consists of an immediate recall phase where participants are read a list of 12 words across three trials (nouns from three taxonomic categories). This is followed by a delayed free recall phase between 20-25 minutes after completion of the immediate recall phase where then participant is asked to recall as many of the words from the list as they can remember. Repetitions and intrusions (words recalled not part of the original list) will also be recorded for each trial. There are 5 validated versions of the HVLT-R and the order of test versions will be randomised for each participant to prevent potential order effects. Delayed recall is measured by how many words are remembered after the delayed free recall phase. More words remembered result in higher scores.

Forward and reverse digit span refers to the longest list of numbers the participant can correctly recall, both in forward and backward order. The task starts at the length of four digits (three for backward) and is increased by one digit for each successful trial. The task is ended when the participant fails to give the correct order after two consecutive attempts. The further participants get in the test the better working memory performance.

State social paranoia scale (SSPS) is a 10-item instrument which measures persecutory thoughts. The persecutory items (e.g. 'someone had bad intentions towards me') are presented among 10 neutral items and scored on a 5-point scale (do not agree - totally agree).

Positive and negative syndrome scale - positive subscale (PANSS-P) is the most common scale to measure psychotic symptoms and commonly used in schizophrenia research. The PANSS is an investigator rated scale and is scored following a semi-structured interview. In this study only the positive subscale will be used, which include the following symptoms: delusions, conceptual disorganisation, hallucinations, hyperactivity, grandiosity, suspiciousness and hostility. The symptoms are scored on a 7-point scale from absent-severe.

Visual analogue scales (VAS) consist of words which describe feeling states and a 100mm horizontal line on which the participant indicates with a vertical line how much of that feeling they have experienced in the moment. The scale ranges from "Not at all" (0mm) to "As much as could possibly be" (100mm).

Visual analogue scales (VAS) consist of words which describe feeling states and a 100mm horizontal line on which the participant indicates with a vertical line how much of that feeling they have experienced in the moment. The scale ranges from "Not at all" (0mm) to "As much as could possibly be" (100mm). Six paranoia VAS from Freeman et al., (2015) will also be included: "Right now I feel suspicious of other people," "Right now I feel that people want to harm me," "Right now I feel like people want to upset me," "Right now I feel like people are against me," "Right now I am thinking that others are trying to persecute me," and "Right now I feel like people are being hostile towards me".

Heart beat will be measured using a standard pulse-oximeter. Systolic blood pressure peaks will be used as a proxy for the R-peak and Inter-beat-intervals will be calculated based on consecutive systolic blood pressure peaks. Heart rate variability will be operationalized as RMSSD based on these inter-beat-intervals.