It is a widely held assumption that the brain performs perceptual inference by combining sensory information with prior expectations, weighted by their uncertainty. A distinction can be made between higher- and lower-level priors, which can be manipulated with associative learning and sensory priming, respectively. Here, we simultaneously investigate priming and the differential effect of auditory vs. visual associative cues on visual perception, and we also examine the reliability of individual differences. Healthy individuals (N = 29) performed a perceptual inference task twice with a one-week delay. They reported the perceived direction of motion of dot pairs, which were preceded by a probabilistic visuo-acoustic cue. In 30% of the trials, motion direction was ambiguous, and in half of these trials, the auditory versus the visual cue predicted opposing directions. Cue-stimulus contingency could change every 40 trials. On ambiguous trials where the visual and the auditory cue predicted conflicting directions of motion, participants made more decisions consistent with the prediction of the acoustic cue. Increased predictive processing under stimulus uncertainty was indicated by slower responses to ambiguous (vs. non-ambiguous) stimuli. Furthermore, priming effects were also observed in that perception of ambiguous stimuli was influenced by perceptual decisions on the previous ambiguous and unambiguous trials as well. Critically, behavioural effects had substantial inter-individual variability which showed high test–retest reliability (intraclass correlation coefficient (ICC) > 0.78). Overall, higher-level priors based on auditory (vs. visual) information had greater influence on visual perception, and lower-level priors were also in action. Importantly, we observed large and stable differences in various aspects of task performance. Computational modelling combined with neuroimaging could allow testing hypotheses regarding the potential mechanisms causing these behavioral effects. The reliability of the behavioural differences implicates that such perceptual inference tasks could be valuable tools during large-scale biomarker and neuroimaging studies.

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<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.