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Background Psychotic symptoms might be explained by disturbances of information processing due to errors of inference during neural coding, and hierarchical models could advance our understanding of how impaired functioning at different levels of the processing hierarchy are associated with psychotic symptoms. However, in order to examine to what extent such alterations are temporary or stable, the psychometric reliability and validity of the measurements need to be established. Individual differences in visual perception were measured by responses to uncertain stimuli presented during a probabilistic associative learning task. Our novel contributions are the measurement of cross-modal (visual and acoustic) associative learning and the assessment of the psychometric properties of indicators derived from a perceptual decision task: we evaluate its internal consistency, test-retest reliability and external validity as shown by associations with schizotypal traits. Methods Participants (32 healthy individuals, 13 men, age (SD) = 27.4 (9.4)) performed a perceptual decision task twice with one week delay. They were asked to indicate the direction of perceived motion of disambiguous and ambiguous visual stimuli (640 trials), which were preceded by visual and acoustic cues that were probabilistically associated with the motion direction and were congruent (both predict the same motion) or incongruent (cues predict different motion). Schizotypal traits were measured with the short version of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE) questionnaire, which showed good internal consistency and test-retest reliability (Cronbach’s alpha: 0.71 – 0.83 for subscales, test-retest correlation for Cognitive Disorganization: r = 0.84, and Unusual Experiences: r = 0.79). Results We found a significant difference in response reaction times between stimuli with high and low probability (t = -2.037; p = 0.044). Acoustic cues predicted the decision significantly higher in case of ambiguous stimuli in both sessions (1. t=4.19, p&amp;lt;0.001; 2: t=3.46, p=0.002). Congruency of visual and acoustic cue pairs had no significant effect on response times for ambiguous stimuli. Reaction times and bias towards reliance on auditory cues during perceptual decision making under uncertainty showed stability over the two sessions (test-retest rho’s ranging from 0.56 – 0.72). Cognitive Disorganization scores showed weak negative correlation with response time under uncertainty (session 1: r= -0.24, session 2: r= -0.28), Unusual Experiences scores showed weak negative correlation with the bias towards reliance on auditory cues (session1: r= -0.21, session 2: r= -0.19). We did not find relationship between general response speed and any O-LIFE subscale scores. Discussion The results show some intraindividual stability of individual differences in perceptual decision making as measured by our paradigm. Participants with higher schiztypal scores tend to have slower response speed under uncertainty and greater bias towards reliance on auditory cues in a small healthy sample which implies it might be useful to measure these variables in clinical population and evaluate the effectiveness of therapeutic interventions or illness progression in follow-up studies. The presented preliminary results derived from descriptive statistics of the behavioral data. Our research group is currently working on fitting a trial-by-trial hierarchical computational model - which includes the representation of uncertainty - to find more detailed individual differences, e.g. the time course of parameter changes while learning in a visual perception task.

S61. COMPUTATIONAL MODELLING OF VISUAL MOTION PERCEPTION AND ITS ASSOCIATION WITH SCHIZOTYPAL TRAITS