Hearing voices inside and outside the head: spatial source monitoring in participants prone to auditory hallucinations.

Introduction: Previous studies of source monitoring and auditory hallucinations (AH) have often conflated spatial source (internal-external) with source agency (self-other). Other studies have used suboptimal manipulations of auditory space (e.g., imagine saying vs. saying aloud). We avoided these problems by presenting experimenter-generated stimuli over headphones in the voice of another person so that the location of the voice sounded either internal or external to the participant's head.

Methods: Participants (N=121) studied 96 words and indicated for each whether it was presented internally or externally (online spatial source monitoring). At test, studied words were presented visually, intermixed randomly with 96 unstudied words. Participants indicated whether each item was old or new (item memory) and whether it was presented internally or externally during study (spatial source memory). Independent measures of memory accuracy and response bias were derived for online source monitoring, item memory and source memory using signal detection theory. Performance on these measures was compared between two groups of 30 participants who scored low or high on a measure of AH proneness.

Results: ANOVAs revealed no differences between the high- and low-AH groups in online spatial source monitoring, item memory, or spatial source memory.

Conclusions: We found no evidence that proneness to AH in a sample of healthy volunteers was related to any of the measures of spatial source monitoring performance. We recommend that the methods introduced be applied to future investigations of spatial source monitoring with patient groups and with individuals at-risk for psychosis.