Systematic Self-Observation of Entoptic Phenomena and Their Relation to Hypnagogia

We report the results of systematic self-observation of entoptics and hypnagogia, in a study whose purpose was to investigate the “entoptic explanation” of hypnagogic imagery (i.e., that entoptic phenomena play a role in the genesis of visual hypnagogic imagery). Employing various experimental manipulations designed to increase the incidence of both phenomena, we were able to show the effectivity of such manipulations on reported incidence of entoptics, but not regarding hypnagogia. Furthermore, the two phenomena seem to be independent, and thus we argue that the entoptic hypothesis cannot be supported. In addition, we report that the frequency of incidence of entoptics is an inverted U-shaped function of level of attention (as defined in this study).