Spatial characteristics of hallucinations associated with sleep paralysis

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.

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.

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).

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.