![]() There are many subtypes of predictive processing models that include self-monitoring approaches ( Farrer and Franck, 2007 Ford and Hoffman, 2013) and Bayesian approaches ( Friston, 2005 Siemerkus et al., 2019). In recent years, predictive processing models have arguably become the dominant approach to explain hallucinations in SSD. What then causes hallucinations in individuals with SSD? This question lacks a straightforward answer as there are many theoretical models of hallucinations. 822).” This definition highlights that hallucinations share many of the same phenomenological features as “true perceptions,” but the key point of divergence lies in the source of the event: true perceptions are caused by external events impressing their features on relevant sensory organs, while hallucinations are not caused by an external source. ![]() Hallucinations can be defined as “perception-like experiences with the clarity and impact of a true perception but without the external stimulation of the relevant sensory organ ( American Psychiatric Association, 2013, p. Auditory hallucinations are the most common type of hallucination in SSD with roughly 60–80% of individuals with SSD reporting hearing voices (e.g., auditory verbal hallucinations) or other sounds that nobody else hears ( Sartorius et al., 1986 McCarthy-Jones, 2012 Waters et al., 2014). Hallucinations are a common symptom of schizophrenia spectrum disorders (SSD), although they are reported to a lesser degree by those with other psychiatric conditions, the general healthy population, and can result from prolonged alcohol and drug misuse ( McCarthy-Jones, 2012). While GW theorists maintain that attention plays an important role, they have not delineated a formal “selection mechanism.” This paper specifies a selection mechanism based upon two central hypotheses: (1) a functional network called the “salience network” plays a critical role in selecting sensory representations for conscious broadcast to the GW in normal (healthy) perception (2) sensory representations become abnormally selected for conscious broadcast to the GW (instead of being filtered out of consciousness) in individuals with SSD that experience hallucinations. Yet, it remains unclear how certain information and representations become selected for conscious processing. No existing theory of hallucinations has specified such a “selection mechanism.” Global Workspace (GW) theorists argue that the brain’s interconnected processors select relevant piece(s) of information for broadcasting to other brain processors, rendering the information accessible to consciousness this process known as “ignition” is associated with synchronized activity across distributed cortical and subcortical brain regions. Yet, it remains unclear how these representations become selected for conscious processing. But how does activity in these regions give rise to aberrant conscious perceptions that seemingly invade ongoing conscious experience? Most existing models assume that sensory representations are sometimes spontaneously activated in the brain, and that these spontaneous activations somehow play a causal role in the generation of hallucinations. Current neuroscience evidence suggests several brain areas are involved in the generation of hallucinations including the sensory cortex, insula, putamen, and hippocampus. Hallucinations are conscious perception-like experiences that are a common symptom of schizophrenia spectrum disorders (SSD). Department of Psychiatry, Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD, United States.
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