Supplementary Material for: The Role of Interoception in Felt Presence and Psychosis Risk

Background: Felt presence (FP) – the sensation of someone nearby without sensory evidence – is common in healthy adults and related to psychosis risk. FP may arise from a misattribution of internal signals to an external source and often occurs when people are alone. Interoception, the ability to perceive one’s own bodily signals, may help to distinguish oneself from others. FP could relate to interoception across several dimensions: through altered signal perception (interoceptive accuracy), insight into their perception (interoceptive insight), and/or self-reported beliefs (interoceptive beliefs). This is the first study that investigates this potential relationship.

Method: 55 healthy adults completed the heartbeat counting task (HBCT) to assess interoceptive accuracy and insight under three ‘social’ conditions: self-view (observing oneself on a screen), other-view (being observed by the experimenter on a screen) and baseline (no viewing). Participants completed the Prodromal Questionnaire-16 (Ising et al., 2012) to screen for psychosis risk, the Inclusion of Other in the Self Scale (Aron et al., 1992) as a measure of self-other overlap, the Multidimensional Assessment of Interoceptive Awareness, and indicated whether they ever had a ‘felt- or sensed-presence experience’ (Y/N).

Results: Psychotic experiences were elevated in individuals with FP, and it was experienced more often in solitude. Overall, the other-view condition reduced both interoceptive accuracy and insight. Distinct interoceptive patterns emerged for FP and psychosis-risk. High-risk was related to lower interoceptive accuracy, particularly when perceived self-other overlap was low. In contrast, individuals with FP showed intact interoceptive insight when the self-other overlap was low. Both FP and psychosis risk were associated with lower trust in bodily signals and tendency to not distract oneself from bodily sensations. Only FP group reported attending to bodily sensations to calm oneself.

Conclusion: Interoceptive accuracy was preserved in those with FP regardless of their psychosis-risk but their trust of and insight into their own bodily signals were reduced. This mismatch may lead to misattributing internal signals to external sources, contributing to FP. However, preserved interoceptive accuracy may support self-regulation, potentially offering a protective effect. These results highlight the potential of interoceptive training to enhance resilience in individuals at risk for psychosis.