Entoptic phenomena – Entoptics (from the Greek, meaning “within vision”), also known as phosphenes, are complex and diverse luminous geometric images derived from the human central nervous system, produced specifically within the optic cortex and characteristic of certain altered states of consciousness, including shamanistic trances. Links between entoptics, altered consciousness, and shamanisms have been explored in a number of visual culture studies. Entoptics have been vociferously debated in rock art research in particular, due to their use in a neuropsychological model proposed by the Southern African rock art researchers David LewisWilliams and Thomas Dowson in order to establish the origins of some rock art imagery in altered-consciousness and related shamanistic practices.
SOURCE:
Historical Dictionary of Shamanism by Graham Harvey and Robert J. Wallis 2007