Systematic Self-Observation of Entoptic Phenomena and Their Relation to Hypnagogia
Imagination, Cognition and Personality March 1, 1991 Joseph Glicksohn, Gailie Friedland, Avi Salach-Nachum
Systematic self-observation of entoptics and hypnagogia found that experimental manipulations increased the reported incidence of entoptics but not hypnagogia. The two phenomena appear to be independent, arguing against the entoptic explanation of hypnagogic imagery. The frequency of entoptics follows an inverted U-shaped function of attention level.