Spatial characteristics of hallucinations associated with sleep paralysis.

Introduction: Spatial properties of hallucinations have received relatively little systematic investigation. We present evidence from a web-based study of the spatial properties of a broad array of hallucinations associated with sleep paralysis. Predictions regarding spatial characteristics of hallucinations were based on proposed neurophysiological mechanisms underlying different types of hallucinations.

Method: Distributions in three dimensions as well as distance and dispersion measures were assessed for 279 experient for two general categories of hallucinations: Intruder hallucinations--including presence, visual, and auditory hallucinations; and Vestibular-Motor (V-M) hallucinations--including floating, flying, illusory motor movements, out-of-body experiences (OBEs), and autoscopy.

Results: For all spatial measures, Confirmatory Factor Analysis revealed that Intruder and V-M hallucinations constituted distinctive factors. In addition, Intruder hallucinations were experienced as occurring close to, usually within a meter of, the experient, whereas V-M hallucinations involved excursions of considerable distance, often beyond the immediate environment. V-M hallucination distance was positively associated with vividness of V-M hallucinations, whereas Intruder hallucination distance was negatively correlated with theoretically related contact hallucinations (pressure, obstructed breathing, pain, choking, and touch).

Conclusion: The differences in the spatial characteristics of Intruder and V-M hallucinations largely corroborated predictions based on the respective hypothesised neural substrates of a threat activated vigilance system and a bodily-self neuromatrix.