Seeing non-existent events: effects of environmental conditions, schizotypal symptoms, and sub-clinical characteristics.

Under conditions of perceptual ambiguity positive schizotypy and positive symptoms of schizophrenia have been associated with a bias towards reporting the presence of an event in its absence. A word detection task was employed (Experiments 1-3; N=211) to explore a number of environmental parameters, such as perceptual ambiguity (speed of stimulus presentation), and the probability of an event, in an effort to identify the empirical laws that modulate this type of bias. Overall, the obtained data suggested that high schizotypy scorers were more prone to false perceptions (false alarms) as compared to their low schizotypy counterparts, although the two groups did not differ with respect to accuracy (correct responses). High perceptual ambiguity increased false perceptions in both high and low schizotypy scorers. False perceptions increased as the probability level of the presented word increased. This tendency was especially pronounced in the high schizotypy group. False perceptions were predicted by positive schizotypy and disposition to hallucinations after controlling for trait anxiety, depression and delusional ideation.