In Philosophy of Psychedelics, Letheby provides a convincing basis for the idea that psychedelics primarily derive their therapeutic potential through mediating favourable changes to self-related belief systems. In this commentary, we take a closer look at the role that contextual factors play in Letheby’s two-factor account of psychedelic therapy. While Letheby acknowledges that psychedelic effects are highly context-dependent, the exact role that context plays in self-modelling during the acute experience is not entirely clear. We argue that context plays an essential (...) role in shaping the ‘discovery’ of alternate self-conceptions during the acute experience. Specifically, users are more likely to experience alterations in self-conception that are consistent with context-dependent features, such as one’s prior mindset and aspects of the external environment. This is consistent with a REBUS model of psychedelic effects, where a corollary effect of relaxing high-level prior beliefs is that the system becomes increasingly sensitised to bottom-up information from lower-level intrinsic sources and the sensory periphery. Furthermore, it may explain why a positive well-intentioned state of mind and a supportive therapeutic environment are more likely to result in positive acute experiences and long-term improvements in mental wellbeing. We see this position as being largely compatible with Letheby’s proposal, but may shift some aspects of its emphasis and framing. In particular, it may conflict with Letheby’s notion that psychedelics lead to a ‘level cognitive playing field’, where self-related hypotheses are thought to be assigned more or less equal probability. (shrink)

According to the predictive coding theory of psychosis, hallucinations and delusions are explained by an overweighing of high-level prior expectations relative to sensory information that leads to false perceptions of meaningful signals. However, it is currently unclear whether the hypothesized overweighing of priors represents a pervasive alteration that extends to the visual modality and takes already effect at early automatic processing stages. Here, we addressed these questions by studying visual perception of socially meaningful stimuli in healthy individuals with varying degrees (...) of psychosis proneness. In a first task, we quantified participants’ prior for detecting faces in visual noise using a Bayesian decision model. In a second task, we measured participants’ prior for detecting direct gaze stimuli that were rendered invisible by continuous flash suppression. We found that the prior for detecting faces in noise correlated with hallucination proneness as well as delusion proneness. The prior for detecting invisible direct gaze was significantly associated with hallucination proneness but not conclusively with delusion proneness. Our results provide evidence for the idea that overly strong high-level priors for automatically detecting socially meaningful stimuli might constitute a processing alteration in psychosis. (shrink)