Juan Carlo Cabato¹ (), Yannik Heidelbach¹, Gizem Yildiz¹, Katja Fiehler¹, Bianca van Kemenade¹; ¹Justus Liebig University Giessen, Germany

Hallucinations, a primary symptom of schizophrenia, are commonly defined as the perception of sensory information despite the lack of corresponding sensory input. Hallucination-like experiences can be studied in signal detection tasks, in which participants have to detect signals in noise. Indeed, patients with schizophrenia report more false alarms than healthy controls, suggesting a general perceptual deficit. Another proposed mechanism underlying hallucinations is the disruption of efference copy signaling. The efference copy is a copy of the motor command, which is used to anticipate the sensory consequences of self-generated actions. These predictions usually lead to perceptual and neural suppression of the sensory action outcomes. Patients with schizophrenia show less suppression of self-generated stimuli than healthy controls. As such, it has been suggested that dysfunctional efference copy mechanisms are the source of hallucinations in schizophrenia. It is still unclear whether psychotic symptoms can be attributed to aberrant efference copy mechanisms, or to dysfunctional perceptual mechanisms in general. To investigate this question, this study employed a signal-detection task with gratings obscured in dynamic noise under both active (self-generated) and passive (externally generated) conditions. Furthermore, participants filled out questionnaires testing for hallucination-proneness. Results showed that false alarms were more frequent in the active condition relative to the passive condition, driven by an increased response bias in the former while perceptual sensitivity (d’) did not significantly differ. Interestingly, the number of false alarms correlated positively with schizotypy scores. Overall, these results show that people are more likely to believe they perceived a stimulus in noise when they generated the stimulus themselves, possibly due to an increased sense of agency. Nevertheless, people scoring high on schizotypy showed a general tendency to report more false alarms, suggesting that schizotypy may be related to dysfunctional perceptual mechanisms that are not specific to action.

Acknowledgements: Deutsche Forschungsgemeinschaft (DFG), SFB/TRR135 Project A10