Biasing predictive processing of interoceptive information affects implicit spirituality but not religiosity

In a predictive processing framework, religiosity and spirituality (R&S) have been linked to increased reliance on prior knowledge and decreased prediction error monitoring. In addition, R&S might be differentially related to processing exteroceptive and interoceptive information. The present study aimed at manipulating different components of the predictive processing model (prior and prediction error monitoring) in interoception, and evaluating the resulting changes in implicit R&S. In a variant of the heartbeat discrimination task (HDT), we used a sham transcranial magnetic stimulation protocol with verbal suggestions to induce priors about a perceived decrease or increase of the heartbeat frequency (Experiment 1). Prediction error monitoring was modulated by manipulating error feedback reliability in an identical HDT (Experiment 2). Results showed that the point of subjective equality shifted towards the direction of the induced prior compared to the baseline condition only in the direction of decreased heartbeat frequency (Experiment 1), while the sensitivity (just noticeable difference) decreased with unreliable error feedback (Experiment 2). Crucially, implicit spirituality, but not religiosity, increased following the prior induction in the HDT in the "decrease" prior group, and this effect was gauged by the prevalence of autistic personality traits. No significant change in R&S was observed after the unreliable error feedback. An increase of implicit spirituality following the successful induction of priors in the interoceptive processing highlights the role of predictive processing in R&S and the stronger relation of interoception with spirituality than with religiosity, supporting the predictive coding account of R&S.