Thought insertion in schizophrenia may arise from altered Bayesian inference within the predictive coding framework. Early 20th-century phenomenological accounts by the Heidelberg School described thought insertion as a self-disturbance involving disrupted inner connectedness of thoughts, which become sensory and feel inserted. Mescaline was used as a model psychosis to explore these mechanisms. The authors propose that reduced precision of context-dependent predictions, relative to sensory precision, increases prediction-error signals for internal events like thoughts. This aberrant salience, analogous to that proposed for external events, leads individuals to interpret thoughts as inserted by an alien agent, similar to delusion formation from aberrant sensory salience.
Hallucinations in schizophrenia may be understood as part of self-disturbances, arising from non-conscious low-level sensory anomalies and a disrupted perception-action cycle, rather than solely from problems of phenomenal consciousness. Historical phenomenological analyses by the Early Heidelberg School (1909–1932), particularly Mayer-Gross, who studied hypnagogic experiences, mescaline-induced model psychoses, and detailed accounts from people with schizophrenia, shaped this view. Debates with contemporaries led to the conclusion that hallucinations in schizophrenia relate to shifts in the organization of consciousness, later influencing Schneider's First Rank Symptoms. The chapter assesses how these early contributions inform current phenomenological understanding of hallucinations.